ArchGDAL.jl

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See: https://github.com/yeesian/ArchGDAL.jl/blob/master/test/test_geometry.jl#L292

I'm trying to fix type stability of geometry creation for performance (some large gains from small changes) but createlinearring is a strange wart to special-case.

Why does it return a wkbLineString? as the comment says, it seems very odd.

I don't really understand. LINEARRING is a non-standard extension of WKT that several projects support. It basically is a closed LINESTRING. The OGRwkbGeometryType has both wkbLineString and wkbLinearRing. GDAL seems to support it with a createlinearring function that creates a LINEARRING on toWKT. But why not use wkbLinearRing as a geometry type? Perhaps because LINESTRING is the more general type, which you can also close by having the first and last coordinate equal?

Yeah seems like something like that. So the question is really in what cases does GDAL actually return wkbLinearRing form ogr_g_getgeometrytype, if ever?

Hard to make things type stable without knowing that. This is a pretty commmon path too - getting rings from a polygon - so it would be good to make it faster.

It seems never, based on this comment:

wkbLinearRing = 101,    /**< non-standard, just for createGeometry() */

From https://github.com/OSGeo/gdal/blob/v3.5.1/ogr/ogr_core.h#L401

Ok great. We can lock in wkbLineString as the type parameter.

Edit: but I guess we still need to handle passing wkbLinearRing but getting back a wkbLineString. So a line or two of special casing for createlinearring.