Adding a linestring to the topology can load topology multiple times

[strk]

I think this is happening starting on the change which implemented cb_getFaceContainingPoint as a wrapper to a plPGSQL rather than C: the loadTopology is loaded multiple times because the plpgsql function will possibly call other C implemented functions GetRingEdges which re-loads the topology again in the same session.

It would be useful to do everything internally to avoid the duplicated topology loading, which should improve speed and possibly also avoid other unwanted effects of such mislayered behaviour

[strk]

WIP merge request: ​https://gitlab.com/postgis/postgis/-/merge_requests/52

[Sandro Santilli <strk@…>]

In b565cc6/git:

Rewrite GetFaceContainingPoint in C

Closes #4962

[strk]

I'm reopening this because the choice of using lw_segment_side to determine the side the query point falls on the closest edge was WRONG and produces invalid results. I'll have to add a regress test for this case and find another solution.

[strk]

Here's an image of the wrong result. The closest segment is in tick red, the line direction goes down, so the point is on the left side, but lw_segment_side returns 1 (right)

[strk]

Regress test pushed to ​https://gitlab.com/postgis/postgis/-/merge_requests/55

[Sandro Santilli <strk@…>]

In 6571dc8/git:

Use angles to determine side of point on edge when closest is a vertex

Closes #4962 again

Includes regress test for getFaceContainingPoint
(failing without the change)