diff options
Diffstat (limited to 'docs/source/htpd.rst')
| -rw-r--r-- | docs/source/htpd.rst | 136 |
1 files changed, 136 insertions, 0 deletions
diff --git a/docs/source/htpd.rst b/docs/source/htpd.rst new file mode 100644 index 00000000..2209c865 --- /dev/null +++ b/docs/source/htpd.rst @@ -0,0 +1,136 @@ +.. _htpd: + +================================================================================ +HTPD +================================================================================ + +.. contents:: Contents + :depth: 2 + :backlinks: none + +This page documents use of the `crs2crs2grid.py` script and the HTDP +(Horizontal Time Dependent Positioning) grid shift modelling program from +NGS/NOAA to produce PROJ.4 compatible grid shift files for fine grade +conversions between various NAD83 epochs and WGS84. Traditionally PROJ.4 has +treated NAD83 and WGS84 as equivalent and failed to distinguish between +different epochs or realizations of those datums. At the scales of much +mapping this is adequate but as interest grows in high resolution imagery and +other high resolution mapping this is inadequate. Also, as the North American +crust drifts over time the displacement between NAD83 and WGS84 grows (more +than one foot over the last two decades). + +Getting and building HTDP +-------------------------------------------------------------------------------- + +The HTDP modelling program is in written FORTRAN. The source and documentation +can be found on the HTDP page at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml + +On linux systems it will be necessary to install `gfortran` or some FORTRAN +compiler. For ubuntu something like the following should work. + +:: + + apt-get install gfortran + +To compile the program do something like the following to produce the binary "htdp" from the source code. + +:: + + gfortran htdp.for -o htdp + +Getting crs2crs2grid.py +-------------------------------------------------------------------------------- + +The `crs2crs2grid.py` script can be found at +https://github.com/OSGeo/gdal/tree/trunk/gdal/swig/python/samples/crs2crs2grid.py + +It depends on having the GDAL Python bindings operational. If they are not +available you will get an error something like the following: + + +:: + + Traceback (most recent call last): + File "./crs2crs2grid.py", line 37, in <module> + from osgeo import gdal, gdal_array, osr + ImportError: No module named osgeo + +Usage +-------------------------------------------------------------------------------- + +:: + + crs2crs2grid.py + <src_crs_id> <src_crs_date> <dst_crs_id> <dst_crs_year> + [-griddef <ul_lon> <ul_lat> <ll_lon> <ll_lat> <lon_count> <lat_count>] + [-htdp <path_to_exe>] [-wrkdir <dirpath>] [-kwf] + -o <output_grid_name> + + -griddef: by default the following values for roughly the continental USA + at a six minute step size are used: + -127 50 -66 25 251 611 + -kwf: keep working files in the working directory for review. + +:: + + crs2crs2grid.py 29 2002.0 8 2002.0 -o nad83_2002.ct2 + +The goal of `crs2crs2grid.py` is to produce a grid shift file for a designated +region. The region is defined using the `-griddef` switch. When missing a +continental US region is used. The script creates a set of sample points for +the grid definition, runs the "htdp" program against it and then parses the +resulting points and computes a point by point shift to encode into the final +grid shift file. By default it is assumed the `htdp` program will be in the +executable path. If not, please provide the path to the executable using the +`-htdp` switch. + +The `htdp` program supports transformations between many CRSes and for each (or +most?) of them you need to provide a date at which the CRS is fixed. The full +set of CRS Ids available in the HTDP program are: + +:: + + 1...NAD_83(2011) (North America tectonic plate fixed) + 29...NAD_83(CORS96) (NAD_83(2011) will be used) + 30...NAD_83(2007) (NAD_83(2011) will be used) + 2...NAD_83(PA11) (Pacific tectonic plate fixed) + 31...NAD_83(PACP00) (NAD 83(PA11) will be used) + 3...NAD_83(MA11) (Mariana tectonic plate fixed) + 32...NAD_83(MARP00) (NAD_83(MA11) will be used) + + 4...WGS_72 16...ITRF92 + 5...WGS_84(transit) = NAD_83(2011) 17...ITRF93 + 6...WGS_84(G730) = ITRF92 18...ITRF94 = ITRF96 + 7...WGS_84(G873) = ITRF96 19...ITRF96 + 8...WGS_84(G1150) = ITRF2000 20...ITRF97 + 9...PNEOS_90 = ITRF90 21...IGS97 = ITRF97 + 10...NEOS_90 = ITRF90 22...ITRF2000 + 11...SIO/MIT_92 = ITRF91 23...IGS00 = ITRF2000 + 12...ITRF88 24...IGb00 = ITRF2000 + 13...ITRF89 25...ITRF2005 + 14...ITRF90 26...IGS05 = ITRF2005 + 15...ITRF91 27...ITRF2008 + 28...IGS08 = ITRF2008 + +The typical use case is mapping from NAD83 on a particular date to WGS84 on +some date. In this case the source CRS Id "29" (NAD_83(CORS96)) and the +destination CRS Id is "8 (WGS_84(G1150)). It is also necessary to select the +source and destination date (epoch). For example: + +:: + + crs2crs2grid.py 29 2002.0 8 2002.0 -o nad83_2002.ct2 + +The output is a CTable2 format grid shift file suitable for use with PROJ.4 +(4.8.0 or newer). It might be utilized something like: + + +:: + + cs2cs +proj=latlong +ellps=GRS80 +nadgrids=./nad83_2002.ct2 +to +proj=latlong +datum=WGS84 + +See Also +-------------------------------------------------------------------------------- + +* http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml - NGS/NOAA page about the HTDP + model and program. Source for the HTDP program can be downloaded from here. |