GEOIDMODEL support

[snowman2]

The GEOIDMODEL tag is in the WKT here:

PROJ/test/unit/test_operation.cpp

Lines 7987 to 7992 in 97bb56f

	" VERTCRS[\"NAVD88 height\",\n"
	" VDATUM[\"North American Vertical Datum 1988\"],\n"
	" CS[vertical,1],\n"
	" AXIS[\"gravity-related height (H)\",up,\n"
	" LENGTHUNIT[\"metre\",1]],\n"
	" GEOIDMODEL[\"GEOID12B\"]]]";

And it is in the PROJ database:

PROJ/data/sql/customizations.sql

Lines 88 to 103 in 97bb56f

	---- Geoid models -----
	INSERT INTO "geoid_model" SELECT 'GEOID99', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'g1999%' AND deprecated = 0;
	INSERT INTO "geoid_model" SELECT 'GEOID03', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'geoid03%' AND deprecated = 0;
	INSERT INTO "geoid_model" SELECT 'GEOID06', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'geoid06%' AND deprecated = 0;
	INSERT INTO "geoid_model" SELECT 'GEOID09', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'geoid09%' AND deprecated = 0;
	-- Geoid12A and Geoid12B are identical
	INSERT INTO "geoid_model" SELECT 'GEOID12A', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'g2012b%' AND deprecated = 0;
	INSERT INTO "geoid_model" SELECT 'GEOID12B', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'g2012b%' AND deprecated = 0;
	INSERT INTO "geoid_model" SELECT 'GEOID18', auth_name, code FROM grid_transformation WHERE auth_name = 'EPSG' AND grid_name LIKE 'g2018%' AND deprecated = 0;

Thoughts on adding:

1. A C-API method to query for GEOIDMODEL in PROJ DB.
2. A C-API method to get the GEOIDMODEL from the CRS if it exists

Number 2 can currently be done via PROJ JSON:

{"$schema":"https://proj.org/schemas/v0.2/projjson.schema.json","type":"VerticalCRS","name":"NAVD88 height","datum":{"type":"VerticalReferenceFrame","name":"North American Vertical Datum 1988"},"coordinate_system":{"subtype":"vertical","axis":[{"name":"Gravity-related height","abbreviation":"H","direction":"up","unit":"metre"}]},"geoid_model":{"name":"GEOID12B"}}

Not really a big need. Currently can be done with PROJ JSON. Just mostly raising for discussion/thoughts.

[snowman2]

Going to close this as it isn't really needed :)