[gdal-dev] Precision Mystery (FGDB)

[Paul Ramsey]

OKAY, found it, and it's an odd one. It has nothing to do with the
shape buffers or the transit into PostGIS... I just wrote a small
program that uses the FGDB API almost exclusively, it only uses OGR to
write the shape buffer.

And the difference is in the declaration of the SRS... when I declare
a UTM srs with the following extra XML

                                    <XOrigin>-5120900</XOrigin>
                                    <YOrigin>-9998100</YOrigin>
                                    <XYScale>10000</XYScale>
                                    <ZOrigin>-100000</ZOrigin>
                                    <ZScale>10000</ZScale>
                                    <MOrigin>-100000</MOrigin>
                                    <MScale>10000</MScale>
                                    <XYTolerance>0.001</XYTolerance>
                                    <ZTolerance>0.001</ZTolerance>
                                    <MTolerance>0.001</MTolerance>
                                    <HighPrecision>true</HighPrecision>

Then writing the POINT(1 2 3) and reading back with ogrinfo I get

FID Column = OBJECTID
Geometry Column = SHAPE
OGRFeature(test):1
  POINT (1 2 3)

But if I omit those lines, I get:

FID Column = OBJECTID
Geometry Column = SHAPE
OGRFeature(test):1
  POINT (1.000001729731139 1.999981429457875 0.0)

Weird precision changes and my Z is gone! So those things matter...
but what do they do...

P.

On Thu, Jun 30, 2011 at 11:52 AM, Peter Baumann
<p.baumann at jacobs-university.de> wrote:
> 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
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
> --
> 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
> "Si forte in alienas manus oberraverit hec peregrina epistola incertis
> ventis dimissa, sed Deo commendata, precamur ut ei reddatur cui soli
> destinata, nec preripiat quisquam non sibi parata." (mail disclaimer, AD
> 1083)
>
>
>
>