[gdal-dev] Identify EPSG SRS_ID from Shapefile SRS Definition

[Andrea Aime]

On Thu, Sep 29, 2011 at 7:21 PM, <Tony.Na at sybase.com> wrote:

>
> Hi fellow GDAL/OGR developers,
> I'm currently developing an OGR data provider module for Sybase SQLAnywhere
> database, which recently supports spatial features in it's version 12
> release. I have a question regarding the best way to evaluate the
> equivalence between two Spatial Reference Systems.  It seems to me that
> when I use ogr2ogr to translate a SQLAnywhere Layer to a shapefile, the
> shapefile data provider calls the morphToESRI() and morphFromESRI
> functions, which strips out all Authority nodes from my original SRS WKT.
> For example, for the SRS “NAD27 / Alaska Albers”, the WKT representation
> before and after the morph follows:
>
>
> Before morph:
>
>
> PROJCS["Albers Equal Area",
>      GEOGCS["NAD27",
>            DATUM["North_American_Datum_1927",
>                  SPHEROID["Clarke 1866", 6378206.4, 294.978698213898,
>                        AUTHORITY["EPSG","7008"]],
>                  TOWGS84[-3,142,183,0,0,0,0],
>                  AUTHORITY["EPSG","6267"]],
>            PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
>            UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9108"]],
>            AUTHORITY["EPSG","4267"]],
>      PROJECTION["Albers_Conic_Equal_Area"],
>      PARAMETER["standard_parallel_1",55],
>      PARAMETER["standard_parallel_2",65],
>      PARAMETER["latitude_of_center",50],
>      PARAMETER["longitude_of_center",-154],
>      PARAMETER["false_easting",0],
>      PARAMETER["false_northing",0],
>      UNIT["us_survey_feet",0.3048006096012192],
>      AUTHORITY["EPSG","2964"]]
>
> After morph:
> PROJCS["Albers_Equal_Area",
>      GEOGCS["GCS_North_American_1927",
>            DATUM["D_North_American_1927",
>                  SPHEROID["Clarke_1866",6378206.4,294.9786982]],
>            PRIMEM["Greenwich",0],
>            UNIT["Degree",0.017453292519943295]],
>      PROJECTION["Albers"],
>      PARAMETER["standard_parallel_1",55],
>      PARAMETER["standard_parallel_2",65],
>      PARAMETER["latitude_of_origin",50],
>      PARAMETER["central_meridian",-154],
>      PARAMETER["false_easting",0],
>      PARAMETER["false_northing",0]
>      ,UNIT["Foot_US",0.30480060960121924]]
>

prj2epsg.org is able to tell you that the above is EPSG:2964, try it out.
It is however based on the GeoTools referencing subsytem, not OGR

Cheers
Andrea


-- 
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Ing. Andrea Aime
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Tech lead

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