[Geojson] Another question: how to represent 3dm positions?

[Arlo Belshee]

I have another question to which I couldn't find an answer in the archives. If it has been previously discussed, please tell me the right search keywords.

I need to represent 3dm data in GeoJSON. But GeoJSON positions specify the coordinates to be [x, y, z, m1, m2, ...]. Any number, but the first 3 are defined to be x, y, and z (if all are present). So, how do I represent 3dm data (position has x, y, and m, but no z).

The best option that I see is to supply a null for the z. Would that break readers?

Another option would be to encode the dimensions of the coordinate system in the CRS, along with its name. The coordinates for 3dz and 3dm would then be indistinguishable; the only difference would be in a non-standard attribute in the CRS. This would certainly confuse GeoJSON clients.

Is there a better option?

And I don't want to encode this in the type. I shouldn't need to have Point3m and Polygon3m, given that I don't need Point2, Point3z, and Point4.

Thanks for any help you can give.

Arlo

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