From ec2b67d5df927f58af7445e589b347bf03698a30 Mon Sep 17 00:00:00 2001 From: Kristian Evers Date: Tue, 6 Mar 2018 09:23:33 +0100 Subject: Remove html folder --- html/gen_parms.html | 276 ---------------------------------------------------- 1 file changed, 276 deletions(-) delete mode 100644 html/gen_parms.html (limited to 'html/gen_parms.html') diff --git a/html/gen_parms.html b/html/gen_parms.html deleted file mode 100644 index 8cd8e161..00000000 --- a/html/gen_parms.html +++ /dev/null @@ -1,276 +0,0 @@ - - -PROJ.4 - General Parameters - - -

PROJ.4 - General Parameters

- -This document attempts to describe a variety of the PROJ.4 parameters -which can be applied to all, or many coordinate system definitions. This -document does not attempt to describe the parameters particular to particular -projection types. Some of these can be found in the GeoTIFF -Projections -Transform List. The definitive documentation for most parameters -is Gerald's original documentation available from the main PROJ.4 page.

- -

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.

- -

pm - 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 the cs2cs argument -lm.

-   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                           (input)
-3d41'16.48"E    0dN 0.000     (output)
-

- -

towgs84 - Datum transformation to WGS84

- -Datum shifts can be approximated by 3 parameter spatial translations (in -geocentric space), or 7 parameter shifts (translation + rotation + scaling). -The parameters to describe this can be described using the towgs84 -parameter.

- -In the three parameter case, the three arguments are the translations to the -geocentric location in meters.

- -For instance, the following demonstrates converting from the Greek GGRS87 -datum to WGS84.

- -

-% 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
-

- -The seven parameter case uses delta_x, delta_y, delta_z, -Rx - rotation X, Ry - rotation Y, Rz - rotation Z, -M_BF - Scaling. The three translation parameters are in meters as -in the three parameter case. The rotational parameters are in seconds of -arc. The scaling is apparently the scale change in parts per million.

- -A more complete discussion of the 3 and 7 parameter transformations can be -found in the EPSG database (trf_method's 9603 and 9606). Within PROJ.4 -the following calculations are used to apply the towgs84 transformation -(going to WGS84). The x, y and z coordinates are in geocentric coordinates. - -Three parameter transformation (simple offsets): - -

-  x[io] = x[io] + defn->datum_params[0];
-  y[io] = y[io] + defn->datum_params[1];
-  z[io] = z[io] + defn->datum_params[2];
-

- -Seven parameter transformation (translation, rotation and scaling): - -

-  #define Dx_BF (defn->datum_params[0])
-  #define Dy_BF (defn->datum_params[1])
-  #define Dz_BF (defn->datum_params[2])
-  #define Rx_BF (defn->datum_params[3])
-  #define Ry_BF (defn->datum_params[4])
-  #define Rz_BF (defn->datum_params[5])
-  #define M_BF  (defn->datum_params[6])
-
-  x_out = M_BF*(       x[io] - Rz_BF*y[io] + Ry_BF*z[io]) + Dx_BF;
-  y_out = M_BF*( Rz_BF*x[io] +       y[io] - Rx_BF*z[io]) + Dy_BF;
-  z_out = M_BF*(-Ry_BF*x[io] + Rx_BF*y[io] +       z[io]) + Dz_BF;
-

- -Note that EPSG method 9607 (coordinate frame rotation) coefficients can be -converted to EPSG method 9606 (position vector 7-parameter) supported by -PROJ.4 by reversing the sign of the rotation vectors. The methods are -otherwise the same.

- -

nadgrids - Grid Based Datum Adjustments

- -In many places (notably North America and Australia) 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.4 currently supports use of grid shift files for shifting between -datums and WGS84 under some circumstances. The grid shift table formats are -ctable (the binary format produced by the PROJ.4 nad2bin program), -NTv1 (the old Canadian format), and NTv2 (.gsb - the new Canadian and -Australian format).

- -Use of grid shifts 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, 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
-

- -

Downloading and Installing Grids

- -The source distribution of PROJ.4 contains only the ntv1_can.dat file. To -get the set of US grid shift files it is necessary to download an additional -distribution of files from the PROJ.4 site, such as - -proj-nad27-1.1.tar.gz. Overlay it on the PROJ.4 source distribution, -and re-configure, compile and install. The distributed ASCII .lla files -are converted into binary (platform specific) files that are installed. -On windows using the nmake /f makefile.vc nadshift command in -the proj\src directory to build and install these files.

- -It appears we can't redistribute the Canadian NTv2 grid shift file freely, -though it is better than the NTv1 file. However, end users can download it -for free from the NRCan web site at - -http://www.geod.nrcan.gc.ca/software/ntv2_e.php. After -downloading it, just dump it in the data directory with the other -installed data files (usually /usr/local/share/proj).

- -

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.
- -
PROJ.4 always assumes that grids contain a shift to NAD83 -(essentially WGS84). Other types of grids might or might not be usable.
- -

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