DM-13905: Change SpherePoint.getVector to return a sphgeom UnitVector3d

[r-owen]

No description provided.

[TallJimbo]

Looks good!

Interesting that some code is simpler now that we're using an object that doesn't distinguish between absolute and relative positions - I've always wondered if having different types for those was worthwhile, and I think this changeset is a small data point suggesting that it wasn't.

[r-owen]

My own opinion is that having different types for point and extent is usually a nuisance. Image.getXY0 is the classic example: much of the time we want to use it as an extent, but sometimes it needs to be treated as a point. I know of exactly one situation where it has proved quite valuable: constructing boxes. It is very clever to have (point, point) and (point, extent) constructors. However I would give that up in a heartbeat in order to be able to stop casting points to extents and vice versa.

[TallJimbo]

Yup, that's a good summary of the big pros and cons.

It's probably a moot point now, but if I had it to do all over again, I'd probably have a single vector class instead of Point and Extent, have a Python Box constructor that required kwargs, and have C++ Box construction go through fromMinMax and fromMinSize static methods.