[fdo-internals] Question about FDOOGRProvider

Jackie Ng jumpinjackie at gmail.com
Thu Mar 27 06:12:15 PDT 2014

Is it worth caching this extent in the provider for future calls to other
spatial context readers from this provider?

An extent of a Spatial Context isn't exactly guaranteed to be an accurate
barometer of the true bounds of a Feature Class (eg. SQL Server's spatial
context bounds are mostly just inferred from the bounds of whatever spatial
indexes have been set for their geometry columns). It seems to be just a
bounds and not *the* bounds of the Feature Class.

The brute force EXTENT() function in MapGuide is a last-resort method for
obtaining the bounds of a Feature Class. This would only be used if there
was no SpatialExtent() function support in the FDO provider (which sadly OGR
is one of). I know the MapGuide Schema Previewer is one such place that uses
such logic.

- Jackie

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