Paul, The one line that I think is making the difference is
<HighPrecision>true</HighPrecision> because, if memory serves me right, it kicks in logic for using 64bit-coordinates internally (actually I remember something about the sign and the mantissa being 53bits - can't recall exactly). ESRI migrated to what they call high precision coordinate system in ArcGIS 9.2<http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Migrating_to_high_precision>. So all the software really expects the coordinate system to be declared that way by now. There is a good white paper on the ESRI site that describes how ArcGIS manages its coordinate systems internally<http://downloads.esri.com/support/whitepapers/ao_/UnderstandingCoordinateManagement_June2007.pdf>. I hope that helps. - Ragi Date: Thu, 30 Jun 2011 13:26:21 -0700 > From: Paul Ramsey <pram...@cleverelephant.ca> > Subject: Re: [gdal-dev] Precision Mystery (FGDB) > To: gdal-dev@lists.osgeo.org > Message-ID: <banlktiknqyhsdkunfndekn3s6gihl5i...@mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > 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. >
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