Le samedi 08 octobre 2011 07:05:31, Etienne Tourigny a écrit :
> A related question:
>
> given an unnamed datum with defined spheroid, PRIMEM and UNIT values,
> is there a way to find a corresponding named datum or EPSG code?
>
You can find a match, but there are often several possible solutions. See on
your examples below.
> I'd be interested in an existing method, or perhaps externalng code or
> table in which I could search for common candidate DATUM definitions,
> and compare using OGRSpatialReference::IsSameGeogCS() .
One method would be to open data/gcs.csv, iterate over the GEOGCS EPSG code in
the first column, make them expanded to full SRS by
OGRSpatialReference::importFromEPSG(), strip the nodes you are not interested
in for the comparisons (AUTHORITY codes), alter the DATUM/SPHEROID names to
"unknown", and finally compare.
>
> e.g
>
> DATUM["unknown",
> SPHEROID["Spheroid",6378137,298.257223563]],
> PRIMEM["Greenwich",0],
> UNIT["degree",0.0174532925199433]]
>
> corresponds to
>
> EPSG: 4326
> or
> DATUM["WGS_1984",
> SPHEROID["WGS 84",6378137,298.257223563,
> AUTHORITY["EPSG","7030"]],
> AUTHORITY["EPSG","6326"]],
> PRIMEM["Greenwich",0],
> UNIT["degree",0.0174532925199433],
> AUTHORITY["EPSG","4326"]]
Or :
GEOGCS["Hartebeesthoek94",
DATUM["Hartebeesthoek94",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","6148"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4148"]]
GEOGCS["Yemen NGN96",
DATUM["Yemen_National_Geodetic_Network_1996",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","6163"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4163"]]
GEOGCS["Korean 1995",
DATUM["Korean_Datum_1995",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","6166"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4166"]]
And other GEOGCS that are defined by "+proj=longlat +ellps=WGS84
+towgs84=0,0,0,0,0,0,0 +no_defs" in the share/proj/epsg file.
>
> also:
>
> DATUM["unknown",
> SPHEROID["Spheroid",6378137,298.2572221010002]],
> PRIMEM["Greenwich",0],
> UNIT["degree",0.0174532925199433]],
>
> corresponds to
> EPSG:4283
> or
> DATUM["Geocentric_Datum_of_Australia_1994",
> SPHEROID["GRS 1980",6378137,298.2572221010002,
> AUTHORITY["EPSG","7019"]],
> TOWGS84[0,0,0,0,0,0,0],
> AUTHORITY["EPSG","6283"]],
> PRIMEM["Greenwich",0],
> UNIT["degree",0.0174532925199433],
> AUTHORITY["EPSG","4283"]],
>
Or :
GEOGCS["TWD97",
DATUM["Taiwan_Datum_1997",
SPHEROID["GRS 1980",6378137,298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","1026"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","3824"]]
GEOGCS["IGRS",
DATUM["Iraqi_Geospatial_Reference_System",
SPHEROID["GRS 1980",6378137,298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","1029"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","3889"]]
GEOGCS["MOLDREF99",
DATUM["MOLDREF99",
SPHEROID["GRS 1980",6378137,298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","1032"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4023"]]
GEOGCS["RGRDC 2005",
DATUM["Reseau_Geodesique_de_la_RDC_2005",
SPHEROID["GRS 1980",6378137,298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","1033"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4046"]]
GEOGCS["SREF98",
DATUM["Serbian_Reference_Network_1998",
SPHEROID["GRS 1980",6378137,298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","1034"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4075"]]
>
> many thanks
> Etienne
>
> On Fri, Oct 7, 2011 at 8:36 PM, Etienne Tourigny
>
> <etourigny....@gmail.com> wrote:
> > Hi all,
> >
> > I would appreciate any hints as to how I can compare 2
> > WKT/OGRSpatialReference objects.
> >
> > My goal is to make sure that a more detailed WKT (with authority codes
> > and explicit datum) corresponds (numerically) to a simpler one, such
> > as in the following examples.
> >
> > I understand that the oSRSGDAL.exportToPrettyWkt() function can remove
> > AXIS, AUTHORITY and EXTENSION nodes, but how can I guarantee that the
> > PARAMETER nodes are in the same order? Does FixupOrdering() solve that
> > problem?
> >
> > Furthermore, How could I compare the datums?
> >
> >
> >
> >
> > CF=[PROJCS["unnamed",
> > GEOGCS["unknown",
> > DATUM["unknown",
> > SPHEROID["Spheroid",6378137,298.2572221010002]],
> > PRIMEM["Greenwich",0],
> > UNIT["degree",0.0174532925199433]],
> > PROJECTION["Lambert_Conformal_Conic_2SP"],
> > PARAMETER["standard_parallel_1",-18],
> > PARAMETER["standard_parallel_2",-36],
> > PARAMETER["latitude_of_origin",0],
> > PARAMETER["central_meridian",134],
> > PARAMETER["false_easting",0],
> > PARAMETER["false_northing",0]]]
> >
> > GDAL=[PROJCS["GDA94 / Geoscience Australia Lambert",
> > GEOGCS["GDA94",
> > DATUM["Geocentric_Datum_of_Australia_1994",
> > SPHEROID["GRS 1980",6378137,298.2572221010002,
> > AUTHORITY["EPSG","7019"]],
> > TOWGS84[0,0,0,0,0,0,0],
> > AUTHORITY["EPSG","6283"]],
> > PRIMEM["Greenwich",0],
> > UNIT["degree",0.0174532925199433],
> > AUTHORITY["EPSG","4283"]],
> > PROJECTION["Lambert_Conformal_Conic_2SP"],
> > PARAMETER["standard_parallel_1",-18],
> > PARAMETER["standard_parallel_2",-36],
> > PARAMETER["latitude_of_origin",0],
> > PARAMETER["central_meridian",134],
> > PARAMETER["false_easting",0],
> > PARAMETER["false_northing",0],
> > UNIT["metre",1,
> > AUTHORITY["EPSG","9001"]],
> > AUTHORITY["EPSG","3112"]]]
> >
> >
> >
> > Another option is exporting to PROJ.4 strings, but there are the
> > +towgs84 that shows up , plus some differences in +datum vs. +ellps.
> >
> > e.g.
> >
> > CF=[+proj=utm +zone=55 +ellps=WGS84 +units=m +no_defs ]
> > GDAL=[+proj=utm +zone=55 +datum=WGS84 +units=m +no_defs ]
> > or
> > CF=[+proj=lcc +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=134 +x_0=0 +y_0=0
> > +ellps=GRS80 +units=m +no_defs ]
> > GDAL=[+proj=lcc +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=134 +x_0=0
> > +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs ]
> >
> >
> >
> > many thanks,
> > Etienne
>
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