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I'm trying to find the actual definition of the curve types supported by PostGIS in WKT.

PostGIS's documentation refers to the " SQL Multimedia Applications Spatial specification":

The SQL Multimedia Applications Spatial specification extends the simple features for SQL spec by defining a number of circularly interpolated curves.

That paper, SQL/MM Spatial - The Standard to Manage Spatial Data in a Relational Database System, defines database functions for interacting with curves (eg, ST_CompoundCurve) but does not define any WKT data types, or give very precise definitions.

The OGC's "Simple Feature Access - Part 1: Common Architecture" standard" provides names and WKB codes for these data types, but doesn't define them further.

So, um, where are the circular curve types in WKT (or is it EWKT? or SQL MM?) actually defined?

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The core types and well-known architecture is defined and standardized in the proprietary

commonly abbreviated as SQL/MM and mentioned in the PostGIS docs (including some examples).


A generic (textual) technical documentation of the supported WKT components and their construction can be found as part of the PostGIS repository docs here.

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