Doc: Add and update check-geometry examples

[geographika]

• Update gdal vector check-geometry example to use AS_WKT as using AS_XY throws errors ERROR 1: Geometry type Multi Point is not compatible with GEOMETRY=AS_XY. since gdal vector check-geometry: write error geometries as MultiPoint #13854
• Add a couple more complex examples, checking folders of datasets and using the handy --no-create-empty-layers option
• Various updates to attempt to clarify some notes about validity
• OGR Simple Features standard should be OGC Simple Features standard
• Fixes a couple of MultiPolyon/MultiPolygon typos

[dbaston]

Odd that this got in, I wonder if the spellcheck misses figure captions.

[geographika]

Strange indeed, as its not in the word list. Maybe camel casing gets ignored?

[dbaston]

Probably out of scope for this PR, but GEOS considers points with NaN coordinates to be invalid. I don't know if that comes from OGR or not. GDAL doesn't bother passing points to GEOS, so in this case GDAL reports valid where GEOS reports invalid.

gdal pipeline read "POINT (3 NaN)" ! check-geometry ! write /vsistdout/ --format CSV
Warning 1: Requested to create spatial CSV layer but GEOMETRY layer creation option not set. No geometry will be output.
Warning 1: Point geometry passed to 'gdal vector check-geometry'. Point geometries are always valid/simple. Further messages of this type will be suppressed.
error

vs

geosop -a "POINT (3 NaN)" isValid
false

[jratike80]

I don't know if that comes from OGR or not.

JTS does not accept "POINT (3 NaN)" either. I cannot imagine what kind of point that would be, but there are other things that I cannot imagine but which are apparently true anyhow.

[geographika]

This sounds like it could cause some confusion, if check-geometry returns valid for a dataset including NaN, and then extents and other calculations are messed up later? Is it worth opening an issue for this? Or I can add a note to the docs?