[gdal-dev] Precision Mystery (FGDB)

[Paul Ramsey]

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