[postgis-devel] LWGEOM: collection type

[Gino Lucrezi]

> Since OGC only defines 'length', what about dropping length3d and length2d ?
> A 3d geom would get a 3d length computed, while a 2d length would get
> a 2d length computed.

It is true that length2d and length3d will yeld the same result for a 2d geom, so in this case there would be no need to have both.

However, when you're using a 3d geometry the two functions would give different results, and you can't predict which one the user will need.
In many instances, I think, even with a 3d geom you'll want the length calculated on a 2d basis, because that's the same result you'd get by doing this calculation on a map. In other instances you'll need the result using the Z coordinate.
So, I think it's better to keep both versions.

Gino Lucrezi
Penta Consulting Services