TIN: Add a workaround in reading WKT/WKB

[lbartoletti]

Description

There is currently no class for managing TIN in QGIS. A TIN is essentially a kind of multipolygon (multi-triangle, as in the OGC sense, a triangle is a specific type of polygon).
This commit enables reading a TIN WKB/WKT and "converts" it into a multipolygon. A dedicated TIN class will be proposed later, after the feature freeze ends and for new QGIS versions.

Funded by : Oslandia, SFCGAL and QGIS

[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit 2cb0434)

[nyalldawson]

I don't think this is suitable for backporting -- it should wait for 3.38 instead.

[nyalldawson]

Suggested change

	TIN = 16, //!< TIN
	TIN = 16, //!< TIN (since QGIS 3.38)

elsewhere too

[nyalldawson]

Don't forget to adapt https://github.com/qgis/QGIS/blob/master/tests/src/python/test_qgsgeometry.py#L3298 too!

[lbartoletti]

I don't think this is suitable for backporting -- it should wait for 3.38 instead.

Why 3.38?

I think, it's OK for 3.36 as a "cast" to multipolygon. For 3.38, I expect to add a true QgsTIN class.

[nyalldawson]

Why 3.38?
I think, it's OK for 3.36 as a "cast" to multipolygon. For 3.38, I expect to add a true QgsTIN class.

What's the benefit in getting just the type in before this? Wouldn't that break things like round trips through wkb?

[lbartoletti]

Why 3.38?
I think, it's OK for 3.36 as a "cast" to multipolygon. For 3.38, I expect to add a true QgsTIN class.

What's the benefit in getting just the type in before this? Wouldn't that break things like round trips through wkb?

After reflection and internal discussion, I have decided to abandon this workaround in favor of implementing full support for TIN (Triangulated Irregular Network) and PolyhedralSurface to fully comply with OGC (Open Geospatial Consortium) Simple Feature standards in version 3.38.