Notes on spatial transforms & spatial topology

[Wumpf]

What

• Fixes Formalize specification/documentation of how transforms interact with heuristics and queries #4655

As discussed on Slack, noted down what we decided on spatial transforms. Extended it a bit from there

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[jleibs]

One thing we might want to introduce is a union-arm like: Transform3D::Unknown which acts as a 3D transform topologically speaking, but will return some kind of "Temporarily disconnected" result during runtime evaluation and prevent the reprojection from taking place.

[Wumpf]

Hmmmm but we shouldn't make this affect our visualizability calculation I think since as you say the "unreachability" is entirely temporary