Merge pull request #577 from OSGeo/docs-release-4.10.0

Docs for the upcoming release

10 files changed, 1243 insertions, 0 deletions

diff --git a/docs/source/usage/apps/cct.rst b/docs/source/usage/apps/cct.rst
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+.. _cct:
+
+================================================================================
+cct
+================================================================================
+
+
+.. Index:: cct
+
+
+
+
+``cct`` a 4D equivalent to the ``proj`` projection
+program, performs transformation coordinate systems on a set of input points.
+The coordinate system transformation can include  translation  between
+projected  and geographic coordinates as well as the application of datum shifts.
+
+cct is an acromyn meaning *Coordinate Conversion and Transformation*.
+
+The acronym refers to definitions given in the OGC 08-015r2/ISO-19111
+standard "Geographical Information -- Spatial Referencing by Coordinates",
+which defines two different classes of *coordinate operations*:
+
+*Coordinate Conversions*, which are coordinate operations where input
+and output datum are identical (e.g. conversion from geographical to
+cartesian coordinates) and
+
+*Coordinate Transformations*, which are coordinate operations where
+input and output datums differ (e.g. change of reference frame).
+
+``cct``, however, also refers to Carl Christian Tscherning (1942--2014),
+professor of Geodesy at the University of Copenhagen, mentor and advisor
+for a generation of Danish geodesists, colleague and collaborator for
+two generations of global geodesists, Secretary General for the
+International Association of Geodesy, IAG (1995--2007), fellow of the
+Amercan Geophysical Union (1991), recipient of the IAG Levallois Medal
+(2007), the European Geosciences Union Vening Meinesz Medal (2008), and
+of numerous other honours.
+
+cct, or Christian, as he was known to most of us, was recognized for his
+good mood, his sharp wit, his tireless work, and his great commitment to
+the development of geodesy -- both through his scientific contributions,
+comprising more than 250 publications, and by his mentoring and teaching
+of the next generations of geodesists.
+
+As Christian was an avid Fortran programmer, and a keen Unix connoiseur,
+he would have enjoyed to know that his initials would be used to name a
+modest Unix style transformation filter, hinting at the tireless aspect
+of his personality, which was certainly one of the reasons he accomplished
+so much, and meant so much to so many people.
+
+Hence, in honour of cct (the geodesist) this is cct (the program).
+
+
+
+Synopsis
+********
+
+::
+
+       cct [ -cotvz [ args ] ]... +opts[=arg]...  file...
+
+Description
+***********
+The following control parameters can  appear  in any order:
+
+::
+
+       -c x,y,z,t
+       --columns=x,y,z,t
+              Specify input columns for (up to) 4 input parameters. Defaults to 1,2,3,4
+
+       -o <output file name>
+       --output=<output file name>
+              Specify the name of the output file.
+
+       -t <time>
+       --time=<time>
+              Specify a fixed observation time to be used for all input data.
+
+      -z <height>
+      --height=<height>
+              Specify a fixed observation height to be used for all input data.
+
+       -v
+       --verbose
+              Write non-essential, but potentially useful, information to stderr.
+              Repeat for additional information (-vv, -vvv, etc.)
+
+The ``+args`` arguments are associated with coordinate operation parameters. Usage varies with
+operation. For a complete description consult the `projection pages <../projections/index.html>`_
+
+
+Examples
+********
+
+1. The operator specs describe the action to be performed by cct. So the following script
+
+::
+
+     echo 12 55 0 0 | cct +proj=utm +zone=32 +ellps=GRS80
+
+will transform the input geographic coordinates into UTM zone 32 coordinates.
+Hence, the command
+
+::
+
+      echo 12 55 | cct -z0 -t0 +proj=utm +zone=32 +ellps=GRS80
+
+Should give results comparable to the classic proj command
+
+::
+
+      echo 12 55 | proj +proj=utm +zone=32 +ellps=GRS80
+
+2. Convert geographical input to UTM zone 32 on the GRS80 ellipsoid:
+
+::
+
+      cct +proj=utm +ellps=GRS80 +zone=32
+
+3. Roundtrip accuracy check for the case above:
+
+::
+
+      cct +proj=pipeline +proj=utm +ellps=GRS80 +zone=32 +step +step +inv
+
+4. As (2) but specify input columns for longitude, latitude, height and time:
+
+::
+
+      cct -c 5,2,1,4  +proj=utm +ellps=GRS80 +zone=32
+
+5. As (2) but specify fixed height and time, hence needing only 2 cols in input:
+
+::
+
+      cct -t 0 -z 0  +proj=utm  +ellps=GRS80  +zone=32
diff --git a/docs/source/usage/apps/cs2cs.rst b/docs/source/usage/apps/cs2cs.rst
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+.. _cs2cs:
+
+================================================================================
+cs2cs
+================================================================================
+
+
+``cs2cs`` performs transformation between the source and destination cartographic  coordinate  system
+on a set of input points.  The coordinate system transformation can include  translation  between
+projected  and geographic coordinates as well as the application of datum shifts.
+
+
+Synopsis
+********
+
+::
+
+       cs2cs [ -eEfIlrstvwW [ args ] ] [ +opts[=arg] ] [ +to [+opts[=arg]] ] file[s]
+
+Description
+***********
+The following control parameters can  appear  in any order:
+
+::
+
+       -I     method to specify inverse translation, convert from +to coordinate system to the
+              primary coordinate system defined.
+
+       -ta    A specifies a character employed as the first character to denote a control  line
+              to  be passed through without processing. This option  applicable  to  ascii  input
+              only. (# is the default value).
+
+       -e string
+              String is an arbitrary string to be output if an error is detected  during  data
+              transformations. The  default value is: *\t*. Note that if the -b, -i or -o
+              options are employed, an error is returned as HUGE_VAL value for both
+              return values.
+
+       -E     causes the input coordinates to be copied to the output line prior to printing  the
+              converted values.
+
+       -l[p|P|=|e|u|d]id
+              List projection identifiers with -l, -lp or -lP (expanded) that can be selected
+              with +proj. -l=id gives expanded description of projection id. List
+              ellipsoid identifiers with -le, that can be selected with +ellps,-lu list  of
+              cartesian to meter conversion factors that can be selected with +units or -ld
+              list of datums that can be selected with +datum.
+
+       -r     This options reverses the order of the expected input from longitude-latitude or
+              x-y to latitude-longitude or y-x.
+
+       -s     This options reverses the order of the output from x-y or longitude-latitude to
+              y-x or latitude-longitude.
+
+       -f format
+              Format is a printf format string to control the form of the output values. For
+              inverse projections, the output will be in degrees when this option is employed.
+              If a format is specified for inverse projection the output data will be in deci-
+              mal  degrees. The default format is "%.2f" for forward projection and DMS for
+              inverse.
+
+       -[w|W]n
+              N is the number of significant fractional digits to employ for seconds output (when
+              the option is not specified, -w3 is assumed). When -W is employed the fields
+              will be constant width and with leading zeroes.
+
+       -v     causes a listing of cartographic control parameters tested for and used by the
+              program to be printed prior to input data.
+
+The ``+args`` run-line arguments are associated with cartographic parameters. Usage varies with
+projection and for a complete description consult the `projection pages <../projections/index.html>`_
+
+The cs2cs program requires two coordinate system
+definitions.  The first (or primary  is  defined
+based on all projection parameters not appearing
+after the +to argument.  All projection  parameters
+appearing  after the ``+to`` argument are considered
+the definition of the second  coordinate
+system.  If there is no second coordinate system
+defined, a geographic coordinate system based on
+the datum and ellipsoid of the source coordinate
+system is assumed.  Note  that  the  source  and
+destination  coordinate  system can both be projections,
+both be geographic, or one of each and
+may have the same or different datums.
+
+Additional  projection control parameters may be
+contained in two auxiliary  control  files:  the
+first   is   optionally   referenced   with  the
+``+init=file:id`` and the second is always processed
+after the name of the projection has been established
+from either the run-line or the  contents
+of  ``+init``   file.   The  environment  parameter
+PROJ_LIB establishes the default directory for a
+file  reference  without an absolute path.  This
+is also used for  supporting  files  like  datum
+shift files.
+
+One  or  more  files (processed in left to right
+order) specify the source of data to  be  transformed.
+A  - will specify the location of processing standard input.
+If no files are  specified,  the  input  is  assumed to be from stdin.
+For input data the two data values  must  be  in
+the  first  two white space separated fields and
+when both input and output are ASCII all  trailing
+portions  of the input line are appended to
+the output line.
+
+Input geographic data (longitude  and  latitude)
+must  be  in  DMS  or decimal degrees format and
+input cartesian data must be in units consistent
+with  the  ellipsoid major axis or sphere radius
+units.  Output geographic coordinates will  normally
+be in DMS format (use ``-f %.12f`` for decimal
+degrees with 12 decimal places), while projected
+(cartesian)   coordinates   will  be  in  linear
+(meter, feet) units.
+
+
+Example
+*******
+The following script
+
+::
+
+     cs2cs +proj=latlong +datum=NAD83
+           +to +proj=utm +zone=10  +datum=NAD27
+     -r <<EOF
+     45d15'33.1"   111.5W
+     45d15.551666667N   -111d30
+     +45.25919444444    111d30'000w
+     EOF
+
+will  transform the input NAD83 geographic coordinates into NAD27
+coordinates in the  UTM  projection  with  zone 10 selected.  The geographic
+values of this example are equivalent and  meant as  examples of various forms of DMS input.
+The x-y output data will appear as three lines of:
+
+::
+
+     1402285.99      5076292.42 0.000
+
+
diff --git a/docs/source/usage/apps/geod.rst b/docs/source/usage/apps/geod.rst
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+.. _geod:
+
+================================================================================
+geod
+================================================================================
+
+``geod``  (direct)  and  ``invgeod`` (inverse) perform geodesic ("Great
+Circle") computations for determining latitude,  longitude  and
+back  azimuth  of  a terminus point given a initial point latitude,
+longitude, azimuth and distance (direct) or  the  forward
+and  back azimuths and distance between an initial and terminus
+point latitudes and  longitudes  (inverse).   The  results  are
+accurate  to  round  off for :math:`|f| < 1/50`, where f is flattening.
+
+
+``invgeod`` may not be available on all  platforms;  in  this  case
+call geod with the -I option.
+
+
+
+Synopsis
+********
+
+::
+
+       geod +ellps=<ellipse> [ -afFIlptwW [ args ] ] [ +args ] file[s]
+
+       invgeod +ellps=<ellipse> [ -afFIlptwW [ args  ]  ]  [  +args  ] file[s]
+
+Description
+***********
+The following command-line options can appear in any order:
+
+::
+
+   -I     Specifies that the inverse geodesic computation is to be
+          performed. May be used with execution of geod as an
+          alternative to invgeod execution.
+
+   -a     Latitude and longitudes of the initial and terminal
+          points, forward and back azimuths and distance are  output.
+
+   -ta    A specifies a character employed as the first character
+          to denote a control line to be passed through without
+          processing.
+
+   -le    Gives a listing of all the ellipsoids that may be
+          selected with the +ellps= option.
+
+   -lu    Gives a listing of all the units that  may  be  selected
+          with the +units= option.
+
+   -[f|F] format
+          Format is a printf format string to control the output
+          form of the geographic coordinate values (f) or distance
+          value (F). The default mode is DMS for geographic
+          coordinates and "%.3f" for distance.
+
+   -[w|W]n
+          N is the number of significant fractional digits to
+          employ for seconds output (when the option is not
+          specified, -w3 is assumed). When -W is employed the fields
+          will be constant width with leading zeroes.
+
+   -p     This option causes the azimuthal values to be output as
+          unsigned DMS numbers between 0 and 360 degrees. Also
+          note -f.
+
+The  ``+args``  command-line  options  are associated with geodetic
+parameters for specifying the ellipsoidal  or  sphere  to  use.
+See  ``proj``  `documentation <proj.html>`_ for full list of these parameters and
+controls.  The options are processed in  left  to  right  order
+from  the  command  line.  Reentry of an option is ignored with
+the first occurrence assumed to be the desired value.
+
+One or more files (processed in left to  right  order)  specify
+the  source  of  data  to be transformed.  A - will specify the
+location of processing standard input.  If no files are  specified,
+the input is assumed to be from stdin.
+
+For  direct determinations input data must be in latitude, longitude,
+azimuth and distance order and output will be latitude,
+longitude  and  back  azimuth of the terminus point.  Latitude,
+longitude of the initial and terminus point are input  for  the
+inverse  mode  and respective forward and back azimuth from the
+initial and terminus points are output along with the  distance
+between the points.
+
+Input  geographic  coordinates  (latitude  and  longitude)  and
+azimuthal data must be in decimal degrees  or  DMS  format  and
+input distance data must be in units consistent with the ellipsoid
+major axis or sphere radius units.  The latitude must  lie
+in the range [-90d,90d].  Output geographic coordinates will be
+in DMS (if the -f switch is not employed) to 0.001" with trailing,
+zero-valued minute-second fields deleted.  Output distance
+data will be in the same  units  as  the  ellipsoid  or  sphere
+radius.
+
+The Earth's ellipsoidal figure may be selected in the same manner
+as program ``proj`` by using ``+ellps=``, ``+a=``, ``+es=``, etc.
+
+Geod may also be used to determine  intermediate  points  along
+either  a  geodesic  line between two points or along an arc of
+specified distance from a geographic point.  In both  cases  an
+initial  point must be specified with ``+lat_1=lat`` and ``+lon_1=lon``
+parameters  and  either  a  terminus   point   ``+lat_2=lat``   and
+``+lon_2=lon``  or  a  distance  and azimuth from the initial point
+with ``+S=distance`` and ``+A=azimuth`` must be specified.
+
+If points along a geodesic are to  be  determined  then  either
+``+n_S=integer``  specifying  the  number  of  intermediate  points
+and/or  ``+del_S=distance``  specifying  the  incremental  distance
+between points must be specified.
+
+To  determine  points along an arc equidistant from the initial
+point both ``+del_A=angle``  and  ``+n_A=integer``  must  be  specified
+which determine the respective angular increments and number of
+points to be determined.
+
+Examples
+********
+
+The following script determines the geodesic azimuths and  distance in U.S.
+statute miles from Boston, MA, to Portland, OR:
+
+::
+
+     geod +ellps=clrk66 <<EOF -I +units=us-mi
+     42d15'N 71d07'W 45d31'N 123d41'W
+     EOF
+
+which gives the results:
+
+::
+
+     -66d31'50.141" 75d39'13.083" 2587.504
+
+where the first two values are the azimuth from Boston to Portland,
+the back azimuth from Portland to Boston followed by the distance.
+
+An  example  of forward geodesic use is to use the Boston location
+and determine Portland's location by azimuth and distance:
+
+::
+
+     geod +ellps=clrk66 <<EOF +units=us-mi
+     42d15'N 71d07'W -66d31'50.141" 2587.504
+     EOF
+
+which gives:
+
+::
+
+     45d31'0.003"N 123d40'59.985"W 75d39'13.094"
+
+.. note::
+    Lack  of precision in the distance value compromises the
+    precision of the Portland location.
+
+Further reading
+***************
+
+#. `GeographicLib <https://geographiclib.sourceforge.io>`_.
+
+#. C. F. F. Karney, `Algorithms for Geodesics <https://doi.org/10.1007/s00190-012-0578-z>`_, J. Geodesy **87**\ (1), 43–55 (2013);
+   `addenda <https://geographiclib.sourceforge.io/geod-addenda.html>`_.
+
+#. `A geodesic bibliography <https://geographiclib.sourceforge.io/geodesic-papers/biblio.html>`_.
diff --git a/docs/source/usage/apps/index.rst b/docs/source/usage/apps/index.rst
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+.. _apps:
+
+================================================================================
+Applications
+================================================================================
+
+Bundled with PROJ comes a set of small command line utilities. The
+``proj`` program is limited to converting between geographic and projection
+coordinates within one datum. The ``cs2cs`` program operates similarly, but
+allows translation between any pair of definable coordinate systems, including
+support for basic datum translation. The ``geod`` program provides the ability
+to do geodesic (great circle) computations.
+
+.. toctree::
+   :maxdepth: 1
+
+   proj
+   cct
+   cs2cs
+   geod
+
diff --git a/docs/source/usage/apps/proj.rst b/docs/source/usage/apps/proj.rst
new file mode 100644
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+++ b/docs/source/usage/apps/proj.rst
@@ -0,0 +1,164 @@
+.. _proj:
+
+================================================================================
+proj
+================================================================================
+
+
+.. Index:: proj
+
+``proj`` and ``invproj`` perform respective forward  and inverse  transformation  of cartographic data to
+or from cartesian data  with  a  wide  range  of selectable projection functions.
+
+
+Synopsis
+********
+::
+
+    proj [ -bcCeEfiIlmorsStTvVwW [ args ] ] [ +args ] file[s]
+    invproj [ -bcCeEfiIlmorsStTwW [ args ] ] [ +args ] file[s]
+
+
+Description
+***********
+The  following  control parameters can appear in any order
+
+::
+
+       -b     Special option for binary coordinate data input and output through standard input
+              and standard output. Data is assumed to be in system type double floating point
+              words. This option is to be used when proj is a son process and allows bypassing
+              formatting operations.
+
+       -i     Selects binary input only (see -b option).
+
+       -C     Check. Invoke all built in self tests and report. Get more verbose report by
+              preceding with the -V option).
+
+       -I     alternate method to specify inverse projection. Redundant when used with invproj.
+
+       -o     Selects binary output only (see -b option).
+
+       -ta    A specifies a character employed as the first character to denote a control line
+              to be passed through without  processing. This  option applicable to ascii input
+              only. (# is the default value).
+
+       -e string
+              String is an arbitrary string to be output if an error is detected during data
+              transformations. The default value is: *\t*. Note that if the -b, -i or -o
+              options are employed, an error is returned as HUGE_VAL value for both return values.
+
+       -E     causes the input coordinates to be copied to the output line prior to printing the
+              converted values.
+
+
+       -l[p|P|=|e|u|d]id
+              List projection identifiers with -l, -lp or -lP (expanded) that can be selected
+              with +proj. -l=id gives expanded description of projection id. List
+              ellipsoid identifiers with -le, that can be selected with +ellps, -lu list of
+              cartesian to meter conversion factors that can be selected with +units or -ld
+              list of datums that can be selected with +datum.
+
+       -r     This options reverses the order of the expected input from longitude-latitude or
+              x-y to latitude-longitude or y-x.
+
+       -s     This options reverses the order of the output from x-y or longitude-latitude to
+              y-x or latitude-longitude.
+
+       -S     Causes estimation of meridional and parallel scale factors, area scale factor and
+              angular distortion, and maximum and minimum scale factors to be listed between <>
+              for each input point. For conformal projections meridional and parallel scales
+              factors will be equal and angular distortion zero. Equal area projections will
+              have an area factor of 1.
+
+       -m mult
+              The cartesian data may be scaled by the mult parameter. When processing data in
+              a forward projection mode the cartesian output values are multiplied by mult
+              otherwise the input cartesian values are divided by mult before inverse projection.
+              If the first two characters of mult are 1/ or 1: then the reciprocal value of mult
+              is employed.
+
+       -f format
+              Format is a printf format string to control the form of the output values. For
+              inverse projections, the output will be in degrees when this option is employed.
+              The  default format is "%.2f" for forward projection and DMS for inverse.
+
+       -[w|W]n
+              N is the number of significant fractional digits to employ for seconds output (when
+              the  option  is  not  specified, -w3 is assumed). When -W is employed the fields
+              will be constant width and  with  leading zeroes.
+
+       -v     causes a listing of cartographic control parameters tested for and used by the
+              program to be printed prior to input data. Should not be used with the -T
+              option.
+
+       -V     This option causes an expanded annotated listing of the characteristics of the
+              projected point. -v is implied with this option.
+
+       -T ulow,uhi,vlow,vhi,res[,umax,vmax]
+              This option creates a set of bivariate Chebyshev polynomial coefficients that
+              approximate the selected  cartographic projection on stdout. The values low and
+              hi denote the range of the input where the u or v prefixes apply to respective
+              longitude-x or latitude-y depending upon whether a forward or inverse projection
+              is selected. Res is an integer number specifying the power of 10 precision of
+              the approximation. For example, a res of -3 specifies an approximation with an
+              accuracy better than .001. Umax, and vmax specify maximum degree of the polynomials
+              (default: 15).
+
+
+The ``+args`` run-line arguments are associated with cartographic parameters. Usage varies with
+projection and for a complete description consult the `projection pages <../projections/index.html>`_
+
+Additional projection control parameters may  be
+contained  in  two  auxiliary control files: the
+first  is   optionally   referenced   with   the
+``+init=file:id`` and the second is always processed
+after the name of the projection has been established
+from either the run-line or the contents
+of  +init  file.   The   environment   parameter
+``PROJ_LIB`` establishes the default directory for a
+file reference without an absolute  path.   This
+is  also  used  for  supporting files like datum
+shift files.
+
+One or more files (processed in  left  to  right
+order)  specify  the source of data to be transformed.
+A - will specify the location  of  processing
+standard input.  If no files are specified,
+the input is assumed  to  be  from  stdin.
+For ASCII input data the two data values must be
+in the first two white  space  separated  fields
+and  when  both  input  and output are ASCII all
+trailing portions of the input line are appended
+to the output line.
+
+Input  geographic  data (longitude and latitude)
+must be in DMS format and input  cartesian  data
+must  be  in units consistent with the ellipsoid
+major axis or sphere radius units.  Output
+geographic  coordinates  will  be in DMS (if the -w
+switch is not employed) and  precise  to  0.001"
+with  trailing, zero-valued minute-second fields
+deleted.
+
+Example
+*******
+The following script
+
+::
+
+     proj +proj=utm  +lon_0=112w  +ellps=clrk66
+     -r <<EOF
+     45d15'33.1"   111.5W
+     45d15.551666667N   -111d30
+     +45.25919444444    111d30'000w
+     EOF
+
+will perform UTM forward projection with a standard
+UTM  central  meridian  nearest  longitude
+112W.  The geographic values of this example are
+equivalent and  meant  as  examples  of  various
+forms  of  DMS  input.  The x-y output data will
+appear as three lines of::
+
+     460769.27     5011648.45
diff --git a/docs/source/usage/environmentvars.rst b/docs/source/usage/environmentvars.rst
new file mode 100644
index 00000000..e1d63543
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+++ b/docs/source/usage/environmentvars.rst
@@ -0,0 +1,43 @@
+.. _environmentvars:
+
+================================================================================
+Environment variables
+================================================================================
+
+PROJ can be crontrolled by setting environment variables. Most users will
+have a use for the :envvar:`PROJ_LIB`.
+
+On UNIX systems environment variables can be set for a shell-session with::
+
+    $ export VAR="some variable"
+
+or it can be set for just one command line call::
+
+    $ VAR="some variable" ./cmd
+
+Environment variables on UNIX are usually removed with the ``unset`` command::
+
+    $ unset VAR
+
+On windows systems environment variables can be set in the command line with::
+
+    > set VAR="some variable"
+
+```VAR`` will be available for the entire session, unless it is unset. This is
+done by setting the variable with no content::
+
+    > set VAR=
+
+.. envvar:: PROJ_LIB
+
+    The location of PROJ :doc:`resource files<../resource_files>`.
+    It is only possible to specify a single library in :envvar:`PROJ_LIB`; e.g. it
+    does not behave like PATH. PROJ is hardcoded to look for resource files
+    in other locations as well, amongst those are the users home directory,
+    ``/usr/share/proj`` and the current folder.
+
+.. envvar:: PROJ_DEBUG
+
+    Set the debug level of PROJ. The default debug level is zero, which results
+    in no debug output when using PROJ. A number from 1-3, whit 3 being the most
+    verbose setting.
diff --git a/docs/source/usage/index.rst b/docs/source/usage/index.rst
new file mode 100644
index 00000000..163aa374
--- /dev/null
+++ b/docs/source/usage/index.rst
@@ -0,0 +1,20 @@
+.. _usage:
+
+================================================================================
+Using PROJ
+================================================================================
+
+The main purpose of PROJ is to transform coordinates from one coordinate
+reference system to another. This can be achieved either with the included
+command line applications or the C API that is a part of the software package.
+
+
+.. toctree::
+   :maxdepth: 1
+
+   quickstart
+   apps/index
+   projections
+   transformation
+   environmentvars
+
diff --git a/docs/source/usage/projections.rst b/docs/source/usage/projections.rst
new file mode 100644
index 00000000..871bc161
--- /dev/null
+++ b/docs/source/usage/projections.rst
@@ -0,0 +1,164 @@
+.. _projections_intro:
+
+================================================================================
+Cartographic projection
+================================================================================
+
+The foundation of PROJ is the large number of
+:doc:`projections<../operations/projections/index>` available in the library. This section
+is devoted to the generic parameters that can be used on any projection in the
+PROJ library.
+
+Below is a list of PROJ parameters which can be applied to most coordinate
+system definitions. This table does not attempt to describe the parameters
+particular to particular projection types. These can be found on the pages
+documenting the individual :doc:`projections<../operations/projections/index>`.
+
+    ==========   ================================================================
+    Parameter    Description
+    ==========   ================================================================
+    +a           Semimajor radius of the ellipsoid axis
+    +axis        Axis orientation
+    +b           Semiminor radius of the ellipsoid axis
+    +ellps       Ellipsoid name (see ``proj -le``)
+    +k           Scaling factor (deprecated)
+    +k_0         Scaling factor
+    +lat_0       Latitude of origin
+    +lon_0       Central meridian
+    +lon_wrap    Center longitude to use for wrapping (see below)
+    +no_defs     Don't use the /usr/share/proj/proj_def.dat defaults file
+    +over        Allow longitude output outside -180 to 180 range, disables
+                 wrapping (see below)
+    +pm          Alternate prime meridian (typically a city name, see below)
+    +proj        Projection name (see ``proj -l``)
+    +units       meters, US survey feet, etc.
+    +vunits      vertical units.
+    +x_0         False easting
+    +y_0         False northing
+    ==========   ================================================================
+
+In the sections below most of the parameters are explained in details.
+
+Units
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+Horizontal units can be specified using the ``+units`` keyword with a symbolic
+name for a unit (ie. ``us-ft``).  Alternatively the translation to meters can be
+specified with the ``+to_meter`` keyword (ie. 0.304800609601219 for US feet).  The
+``-lu`` argument to ``cs2cs`` or ``proj`` can be used to list symbolic unit names.
+The default unit for projected coordinates is the meter.
+A few special projections deviate from this behaviour, most notably the
+latlong pseudo-projection that returns degrees.
+
+Vertical (Z) units can be specified using the ``+vunits`` keyword with a
+symbolic name for a unit (ie. ``us-ft``).  Alternatively the translation to
+meters can be specified with the ``+vto_meter`` keyword (ie. 0.304800609601219
+for US feet).  The ``-lu`` argument to ``cs2cs`` or ``proj`` can be used to list
+symbolic unit names.  If no vertical units are specified, the vertical units will
+default to be the same as the horizontal coordinates.
+
+.. note::
+    ``proj`` do not handle vertical units at all and hence the ``+vto_meter``
+    argument will be ignored.
+
+Scaling of output units can be done by applying the ``+k_0`` argument. The
+returned coordinates are scaled by the value assigned with the ``+k_0``
+parameter.
+
+False Easting/Northing
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+Virtually all coordinate systems allow for the presence of a false easting
+(``+x_0``) and northing (``+y_0``).  Note that these values are always expressed in
+meters even if the coordinate system is some other units.  Some coordinate
+systems (such as UTM) have implicit false easting and northing values.
+
+Longitude Wrapping
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+By default PROJ wraps output longitudes in the range -180 to 180.  The ``+over``
+switch can be used to disable the default wrapping which is done at a low level
+in ``pj_inv()``.  This is particularly useful with projections like the
+:doc:`equidistant cylindrical<../operations/projections/eqc>`
+where it would be desirable for X values past -20000000 (roughly) to continue
+past -180 instead of wrapping to +180.
+
+The ``+lon_wrap`` option can be used to provide an alternative means of doing
+longitude wrapping within ``pj_transform()``.  The argument to this option is a
+center longitude.  So ``+lon_wrap=180`` means wrap longitudes in the range 0 to
+360.  Note that ``+over`` does **not** disable ``+lon_wrap``.
+
+Prime Meridian
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+A prime meridian may be declared indicating the offset between the prime
+meridian of the declared coordinate system and that of greenwich.  A prime
+meridian is clared using the "pm" parameter, and may be assigned a symbolic
+name, or the longitude of the alternative prime meridian relative to greenwich.
+
+Currently prime meridian declarations are only utilized by the
+``pj_transform()`` API call, not the ``pj_inv()`` and ``pj_fwd()`` calls.
+Consequently the user utility ``cs2cs`` does honour prime meridians but the
+``proj`` user utility ignores them.
+
+The following predeclared prime meridian names are supported.  These can be
+listed using with ``cs2cs -lm``.
+
+ ===========     ================
+ Meridian        Longitude
+ ===========     ================
+   greenwich     0dE
+      lisbon     9d07'54.862"W
+       paris     2d20'14.025"E
+      bogota     74d04'51.3"E
+      madrid     3d41'16.48"W
+        rome     12d27'8.4"E
+        bern     7d26'22.5"E
+     jakarta     106d48'27.79"E
+       ferro     17d40'W
+    brussels     4d22'4.71"E
+   stockholm     18d3'29.8"E
+      athens     23d42'58.815"E
+        oslo     10d43'22.5"E
+ ===========     ================
+
+Example of use.  The location ``long=0``, ``lat=0`` in the greenwich based lat/long
+coordinates is translated to lat/long coordinates with Madrid as the prime
+meridian.
+
+::
+
+    cs2cs +proj=latlong +datum=WGS84 +to +proj=latlong +datum=WGS84 +pm=madrid
+    0 0                           <i>(input)</i>
+    3d41'16.48"E    0dN 0.000     <i>(output)</i>
+
+
+Axis orientation
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+Starting in PROJ 4.8.0, the +axis argument can be used to control the axis
+orientation of the coordinate system.  The default orientation is "easting,
+northing, up" but directions can be flipped, or axes flipped using combinations
+of the axes in the +axis switch.  The values are:
+
+* "e" - Easting
+* "w" - Westing
+* "n" - Northing
+* "s" - Southing
+* "u" - Up
+* "d" - Down
+
+They can be combined in +axis in forms like:
+
+* ``+axis=enu`` - the default easting, northing, elevation.
+* ``+axis=neu`` - northing, easting, up - useful for "lat/long" geographic
+  coordinates, or south orientated transverse mercator.
+* ``+axis=wnu`` - westing, northing, up - some planetary coordinate systems
+  have "west positive" coordinate systems
+
+.. note::
+
+    The ``+axis`` argument does not work with the ``proj`` command line
+    utility.
+
+
diff --git a/docs/source/usage/quickstart.rst b/docs/source/usage/quickstart.rst
new file mode 100644
index 00000000..077e970c
--- /dev/null
+++ b/docs/source/usage/quickstart.rst
@@ -0,0 +1,68 @@
+.. _quickstart:
+
+================================================================================
+Quick start
+================================================================================
+
+Coordinate transformations are defined by, what in PROJ terminology is
+known as, "proj-strings". A proj-string describes any transformation regardless of
+how simple or complicated it might be. The simplest case is projection of geodetic
+coordinates. This section focuses on the simpler cases and introduces the basic
+anatomy of the proj-string. The complex cases are discussed in
+:doc:`transformation`.
+
+A proj-strings holds the parameters of a given coordinate transformation, e.g.
+
+::
+
+    +proj=merc +lat_ts=56.5 +ellps=GRS80
+
+I.e. a proj-string consists of a projection specifier, ``+proj``, a number of
+parameters that applies to the projection and, if needed, a description of a
+datum shift. In the example above geodetic coordinates are transformed to
+projected space with the :doc:`Mercator projection<../operations/projections/merc>` with
+the latitude of true scale at 56.5 degrees north on the GRS80 ellipsoid. Every
+projection in PROJ is identified by a shorthand such as ``merc`` in the above
+example.
+
+By using the  above projection definition as parameters for the command line
+utility ``proj`` we can convert the geodetic coordinates to projected space:
+
+::
+
+    $ proj +proj=merc +lat_ts=56.5 +ellps=GRS80
+
+If called as above ``proj`` will be in interactive mode, letting you type the
+input data manually and getting a responce presented on screen. ``proj``
+works as any UNIX filter though, which means that you can also pipe data to
+the utility, for instance by using the ``echo`` command:
+
+::
+
+    $ echo 55.2 12.2 | proj +proj=merc +lat_ts=56.5 +ellps=GRS80
+    3399483.80      752085.60
+
+
+PROJ also comes bundled with the ``cs2cs`` utility which is used to transform
+from onecoordinate reference system to another. Say we want to convert
+the above Mercator coordinates to UTM, we can do that with ``cs2cs``:
+
+::
+
+    $ echo 3399483.80 752085.60 | cs2cs +proj=merc +lat_ts=56.5 +ellps=GRS80 +to +proj=utm +zone=32
+    6103992.36      1924052.47 0.00
+
+Notice the ``+to`` parameter that seperates the source and destination
+projection definitions.
+
+If you happen to know the EPSG identifiers for the two cordinates reference
+systems you are transforming between you can use those with ``cs2cs``:
+
+::
+
+   $ echo 56 12 | cs2cs +init=epsg:4326 +to +init=epsg:25832
+   231950.54      1920310.71 0.00
+
+In the above example we transform geodetic coordinates in the WGS84 reference
+frame to UTM zone 32N coordinates in the ETRS89 reference frame.
+UTM coordinates 
diff --git a/docs/source/usage/transformation.rst b/docs/source/usage/transformation.rst
new file mode 100644
index 00000000..fd1f2f94
--- /dev/null
+++ b/docs/source/usage/transformation.rst
@@ -0,0 +1,314 @@
+.. _transformation:
+
+================================================================================
+Geodetic transformation
+================================================================================
+
+PROJ can do everything from the most simple projection to very complex
+transformations across many reference frames. While originally developed as a
+tool for cartographic projections, PROJ has over time evolved into a powerfull
+generic coordinate transformation engine that makes it possible to do both
+large scale cartographic projections as well as coordinate transformation at a
+geodetic high precision level. This chapter delves into the details of how
+geodetec transformations of varying complexity can be performed.
+
+In PROJ, two frameworks for geodetic transformations exists, the *cs2cs*
+framework and the *transformation pipelines* framework. The first is the original,
+and limited, framework for doing geodetic transforms in PROJ The latter is a
+newer addition that aims to be a more complete transformation framework. Both are
+described in the sections below. Large portions of the text are based on
+[EversKnudsen2017]_.
+
+Before describing the details of the two frameworks, let us first remark that
+most cases of geodetic transformations can be expressed as a series of elementary
+operations, the output of one operation being the input of the next. E.g. when
+going from UTM zone 32, datum ED50, to UTM zone 32, datum ETRS89, one must, in the
+simplest case, go through 5 steps:
+
+1. Back-project the UTM coordinates to geographic coordinates
+2. Convert the geographic coordinates to 3D cartesian geocentric coordinates
+3. Apply a Helmert transformation from ED50 to ETRS89
+4. Convert back from cartesian to geographic coordinates
+5. Finally project the geographic coordinates to UTM zone 32 planar coordinates.
+
+
+Transformation pipelines
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+The homology between the above steps and a Unix shell style pipeline is evident.
+It is there the main architectural inspiration behind the transformation pipeline
+framework. The pipeline framework is realized by utilizing a special "projection",
+that takes as its user supplied arguments, a series of elementary operations,
+which it strings together in order to implement the full transformation needed.
+Additionally, a number of elementary geodetic operations, including Helmert
+transformations, general high order polynomial shifts and the Molodensky
+transformation are available as part of the pipeline framework.
+In anticipation of upcoming support for full time-varying transformations, we
+also introduce a 4D spatiotemporal data type, and a programming interface
+(API) for handling this.
+
+The Molodensky transformation converts directly from geodetic coordinates
+in one datum, to geodetic coordinates in another datum, while the (typically more
+accurate) Helmert transformation converts from 3D cartesian to 3D cartesian
+coordinates. So when using the Helmert transformation one typically needs to do an
+initial conversion from geodetic to cartesian coordinates, and a final conversion
+the other way round, to arrive at the desired result. Fortunately, this three-step
+compound transformation has the attractive characteristic that each step depends
+only on the output of the immediately preceding step. Hence, we can build a
+geodetic-to-geodetic Helmert transformation by tying together the outputs and inputs
+of 3 steps (geodetic-to-cartesian → Helmert → cartesian-to-geodetic), pipeline style.
+The pipeline driver, makes this kind of chained transformations possible.
+The implementation is compact, consisting of just one pseudo-projection, called
+``pipeline``, which takes as its arguments strings of elementary projections
+(note: "projection" is the, slightly misleading, PROJ term used for any kind of
+transformation).
+The pipeline pseudo projection is supplemented by a number of elementary
+transformations, all in all providing a framework for building high accuracy
+solutions for a wide spectrum of geodetic tasks.
+
+
+As a first example, let us take a look at the iconic
+*geodetic → Cartesian → Helmert → geodetic* case (steps 2 to 4 in the example in
+the itroduction). In PROJ it can be implemented as
+
+::
+
+    proj=pipeline
+    step proj=cart ellps=intl
+    step proj=helmert
+         x=-81.0703  y=-89.3603  z=-115.7526
+        rx=-0.48488 ry=-0.02436 rz=-0.41321  s=-0.540645
+    step proj=cart inv ellps=GRS80
+
+The pipeline can be expanded at both ends to accommodate whatever coordinate type
+is needed for input and output: In the example below, we transform from the
+deprecated Danish System 45, a 2D system with some tension in the original defining
+network, to UTM zone 33, ETRS89. The tension is reduced using a polynomial
+transformation (the init=./s45b... step, s45b.pol is a file containing the
+polynomial coefficients), taking the S45 coordinates to a technical coordinate
+system (TC32), defined to represent "UTM zone 32 coordinates, as they would look if
+the Helmert transformation between ED50 and ETRS89 was perfect". The TC32
+coordinates are then converted back to geodetic(ED50) coordinates, using an
+inverse UTM projection, further to cartesian(ED50), then to cartesian(ETRS89),
+using the relevant Helmert transformation, and back to geodetic(ETRS89), before
+finally being projected onto the UTM zone 33, ETRS89 system. All in all a 6 step
+pipeline, implementing a transformation with centimeter level accuracy from a
+deprecated system with decimeter level tensions.
+
+::
+
+    proj=pipeline
+    step init=./s45b.pol:s45b_tc32
+    step proj=utm inv ellps=intl zone=32
+    step proj=cart ellps=intl
+    step proj=helmert
+          x=-81.0703  y=-89.3603  z=-115.7526
+         rx=-0.48488 ry=-0.02436 rz=-0.41321 s=-0.540645
+    step proj=cart inv ellps=GRS80
+    step proj=utm ellps=GRS80 zone=33
+
+With the pipeline framework spatiotemporal transformation is possible. This is
+possible by leveraging the time dimension in PROJ that enables 4D coordinates
+(three spatial components and one temporal component) to be passed through a
+transformation pipeline. In the example below a transformation from ITRF93 to
+ITRF2000 is defined. The temporal component is given as GPS weeks in the input
+data, but the 14-parameter Helmert transform expects temporal units in decimalyears.
+Hence the first step in the pipeline is the unitconvert pseudo-projection that makes
+sure the correct units are passed along to the Helmert transform.
+Most parameters of the Helmert transform are taken from [AltamimiEtAl2002]_,
+except the epoch which is the epoch of the transformation. The default setting is to
+use “coordinate frame” convention of the Helmert transform, but “position vector”
+convention can also be used. The last step in the pipeline is converting the
+coordinate timestamps back to GPS weeks.
+
+::
+
+    proj=pipeline
+    step proj=unitconvert t_in=gps_week t_out=decimalyear
+    step proj=helmert
+         x=0.0127 y=0.0065 z=-0.0209 s=0.00195
+         rx=0.00039 ry=-0.00080 rz=0.00114
+         dx=-0.0029 dy=-0.0002 dz=-0.0006 ds=0.00001
+         drx=0.00011 dry=0.00019 drz=-0.00007
+         epoch=1988.0
+    step proj=unitconvert t_in=decimalyear t_out=gps_week
+
+
+cs2cs paradigm
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+    ============   ==============================================================
+    Parameter      Description
+    ============   ==============================================================
+    +datum         Datum name (see ``proj -ld``)
+    +geoidgrids    Filename of GTX grid file to use for vertical datum transforms
+    +nadgrids      Filename of NTv2 grid file to use for datum transforms
+    +towgs84       3 or 7 term datum transform parameters
+    +to_meter      Multiplier to convert map units to 1.0m
+    +vto_meter     Vertical conversion to meters
+    ============   ==============================================================
+
+The *cs2cs* framework delivers a subset of the geodetic transformations available
+with the *pipeline* framework. Coordinate transformations done in this framework
+are transformed in a two-step process with WGS84 as a pivot datum That is, the
+input coordinates are transformed to WGS84 geodetic coordinates and then transformed
+from WGS84 coordinates to the specified output coordinate reference system, by
+utilizing either the Helmert transform, datum shift grids or a combination of both.
+Datum shifts can be described in a proj-string with the parameters ``+towgs84``,
+``+nadgrids`` and ``+geoidgrids``.
+An inverse transform exists for all three and is applied if
+specified in the input proj-string. The most common is ``+towgs84``, which is used to
+define a 3- or 7-parameter Helmert shift from the input reference frame to WGS84.
+Exactly which realization of WGS84 is not specified, hence a fair amount of
+uncertainty is introduced in this step of the transformation. With the +nadgrids
+parameter a non-lineaer planar correction derived from interpolation in a
+correction grid can be applied. Originally this was implemented as a means to
+transform coordinates between the american datums NAD27 and NAD83, but corrections
+can be applied for any datum for which a correction grid exists. The inverse
+transform for the horizontal grid shift is "dumb", in the sense that the
+correction grid is applied verbatim without taking into account that the inverse
+operation is non-linear. Similar to the horizontal grid correction, ``+geoidgrids``
+can be used to perform grid corrections in the vertical component.
+Both grid correction methods allow inclusion of more than one grid in the same
+transformation
+
+In contrast to the *transformation pipeline* framework, transformations with the
+*cs2cs* framework are expressed as two separate proj-strings. One proj-string *to*
+WGS84 and one *from* WGS84. Together they form the mapping from the source
+coordinate reference system to the destination coordinate reference system.
+When used with the ``cs2cs`` the source and destination CRS's are separated by the
+special ``+to`` parameter.
+
+The following example demonstrates converting from the Greek GGRS87 datum
+to WGS84 with the ``+towgs84`` parameter.
+
+::
+
+    cs2cs +proj=latlong +ellps=GRS80 +towgs84=-199.87,74.79,246.62
+        +to +proj=latlong +datum=WGS84
+    20 35
+    20d0'5.467"E    35d0'9.575"N 8.570
+
+The EPSG database provides this example for transforming from WGS72 to WGS84
+using an approximated 7 parameter transformation.
+
+::
+
+    cs2cs +proj=latlong +ellps=WGS72 +towgs84=0,0,4.5,0,0,0.554,0.219 \
+        +to +proj=latlong +datum=WGS84
+    4 55
+    4d0'0.554"E     55d0'0.09"N 3.223
+
+
+Grid Based Datum Adjustments
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+In many places (notably North America and Austrialia) national geodetic
+organizations provide grid shift files for converting between different datums,
+such as NAD27 to NAD83.  These grid shift files include a shift to be applied
+at each grid location. Actually grid shifts are normally computed based on an
+interpolation between the containing four grid points.
+
+PROJ supports use of grid files for shifting between various reference frames.
+The grid shift table formats are ctable (the binary format produced by the PROJ
+``nad2bin`` program), NTv1 (the old Canadian format), and NTv2 (``.gsb`` - the new
+Canadian and Australian format).
+
+The text in this section is based on the *cs2cs* framework. Gridshifting is off
+course also possible with the *pipeline* framework. The major difference between the
+two is that the *cs2cs* framework is limited to grid mappings to WGS84, whereas with
+*transformation pipelines* it is possible to perform grid shifts between any two
+reference frames, as long as a grid exists.
+
+Use of grid shifts with ``cs2cs`` is specified using the ``+nadgrids``
+keyword in a coordinate system definition. For example:
+
+::
+
+    % cs2cs +proj=latlong +ellps=clrk66 +nadgrids=ntv1_can.dat \
+        +to +proj=latlong +ellps=GRS80 +datum=NAD83 << EOF
+    -111 50
+    EOF
+    111d0'2.952"W   50d0'0.111"N 0.000
+
+In this case the ``/usr/local/share/proj/ntv1_can.dat`` grid shift file was
+loaded, and used to get a grid shift value for the selected point.
+
+It is possible to list multiple grid shift files, in which case each will be
+tried in turn till one is found that contains the point being transformed.
+
+::
+
+    cs2cs +proj=latlong +ellps=clrk66 \
+              +nadgrids=conus,alaska,hawaii,stgeorge,stlrnc,stpaul \
+        +to +proj=latlong +ellps=GRS80 +datum=NAD83 << EOF
+    -111 44
+    EOF
+    111d0'2.788"W   43d59'59.725"N 0.000
+
+
+Skipping Missing Grids
+................................................................................
+
+The special prefix ``@`` may be prefixed to a grid to make it optional.  If it
+not found, the search will continue to the next grid.  Normally any grid not
+found will cause an error.  For instance, the following would use the
+``ntv2_0.gsb`` file if available (see :ref:`nonfreegrids`), otherwise it would
+fallback to using the ``ntv1_can.dat`` file.
+
+::
+
+    cs2cs +proj=latlong +ellps=clrk66 +nadgrids=@ntv2_0.gsb,ntv1_can.dat \
+        +to +proj=latlong +ellps=GRS80 +datum=NAD83 << EOF
+    -111 50
+    EOF
+    111d0'3.006"W   50d0'0.103"N 0.000
+
+The null Grid
+................................................................................
+
+A special ``null`` grid shift file is shift with releases after 4.4.6 (not
+inclusive).  This file provides a zero shift for the whole world.  It may be
+listed at the end of a nadgrids file list if you want a zero shift to be
+applied to points outside the valid region of all the other grids.  Normally if
+no grid is found that contains the point to be transformed an error will occur.
+
+::
+
+    cs2cs +proj=latlong +ellps=clrk66 +nadgrids=conus,null \
+        +to +proj=latlong +ellps=GRS80 +datum=NAD83 << EOF
+    -111 45
+    EOF
+    111d0'3.006"W   50d0'0.103"N 0.000
+
+    cs2cs +proj=latlong +ellps=clrk66 +nadgrids=conus,null \
+        +to +proj=latlong +ellps=GRS80 +datum=NAD83 << EOF
+    -111 44
+    -111 55
+    EOF
+    111d0'2.788"W   43d59'59.725"N 0.000
+    111dW   55dN 0.000
+
+For more information see the chapter on :ref:`transformation_grids`.
+
+Caveats
+................................................................................
+
+* Where grids overlap (such as conus and ntv1_can.dat for instance) the first
+  found for a point will be used regardless of whether it is appropriate or
+  not.  So, for instance, ``+nadgrids=ntv1_can.dat``,conus would result in
+  the Canadian data being used for some areas in the northern United States
+  even though the conus data is the approved data to use for the area.
+  Careful selection of files and file order is necessary.  In some cases
+  border spanning datasets may need to be pre-segmented into Canadian and
+  American points so they can be properly grid shifted
+* There are additional grids for shifting between NAD83 and various HPGN
+  versions of the NAD83 datum.  Use of these haven't been tried recently so
+  you may encounter problems.  The FL.lla, WO.lla, MD.lla, TN.lla and WI.lla
+  are examples of high precision grid shifts.  Take care!
+* Additional detail on the grid shift being applied can be found by setting
+  the PROJ_DEBUG environment variable to a value.  This will result in output
+  to stderr on what grid is used to shift points, the bounds of the various
+  grids loaded and so forth
+* The *cs2cs* framework always assumes that grids contain a shift **to**  NAD83 (essentially
+  WGS84). Other types of grids can be used with the *pipeline* framework.