[gdal-dev] Precision Mystery (FGDB)

[Peter Baumann]

to retain the 3rd dimension, maybe better use WGS84-3D, EPSG:4329 ?
-Peter


On 06/30/2011 08:45 PM, Paul Ramsey wrote:
> In running a round trip from PostGIS>FGDB>PostGIS for a simple table:
>
> 3dgeom=# select st_asewkt(g) from points ;
>         st_asewkt
> ------------------------
>   SRID=4326;POINT(1 2 3)
>   SRID=4326;POINT(2 3 4)
>   SRID=4326;POINT(3 4 5)
>
> When I get to FGDB, I've lost my third dimension (still trying to
> figure that out)
>
> [pramsey at localhost postgis2fgdb]$ ../gdal-svn/gdal/apps/ogrinfo -al ~/3dgeom.gdb
> INFO: Open of `/home/pramsey/3dgeom.gdb'
>        using driver `FileGDB' successful.
>
> Layer name: points
> Geometry: 3D Point
> Feature Count: 3
> Layer SRS WKT:
> GEOGCS["WGS 84",
>      DATUM["WGS_1984",
>          SPHEROID["WGS 84",6378137,298.257223563,
>              AUTHORITY["EPSG","7030"]],
>          AUTHORITY["EPSG","6326"]],
>      PRIMEM["Greenwich",0,
>          AUTHORITY["EPSG","8901"]],
>      UNIT["degree",0.0174532925199433,
>          AUTHORITY["EPSG","9122"]],
>      AUTHORITY["EPSG","4326"]]
> FID Column = OBJECTID
> Geometry Column = g
> OGRFeature(points):1
>    POINT (1.0 2.0 0.0)
>
> OGRFeature(points):2
>    POINT (2.0 3.0 0.0)
>
> OGRFeature(points):3
>    POINT (3.0 4.0 0.0)
>
> But even odder, when I go back to PostGIS, I've got slight coordinate drift.
>
> 3dgeom2=# select st_asewkt(g) from points ;
>                                  st_asewkt
> --------------------------------------------------------------------------
>   SRID=4326;POINT(1.00000000000005 2.00000000000001 1.04446235346063e-305)
>   SRID=4326;POINT(2.00000000000005 3.00000000000001 1.04446235346063e-305)
>   SRID=4326;POINT(3.00000000000005 4.00000000000001 1.04446235346063e-305)
> (3 rows)
>
> I just turned on statement logging and watched both the export and the
> import to PostGIS and in both cases the database is sending and
> receiving the canonical form (hex ewkb) there is no text
> representation step. This seems frightfully odd. Any suggestions on
> debugging steps?
>
> Paul
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-- 
Dr. Peter Baumann
  - Professor of Computer Science, Jacobs University Bremen
    www.faculty.jacobs-university.de/pbaumann
    mail: p.baumann at jacobs-university.de
    tel: +49-421-200-3178, fax: +49-421-200-493178
  - Executive Director, rasdaman GmbH Bremen (HRB 26793)
    www.rasdaman.com, mail: baumann at rasdaman.com
    tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
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