Proposal: New function ST_RemoveIrrelevantPointsForView()

[gluser1357]

I'd like to contribute a new Postgis function, ST_RemoveIrrelevantPointsForView (the_geom, bbox).

This function removes all coordinates being irrelevant for rendering data within a given view. In contrast to ST_Intersection(), no new coordinates will be computed. The function currently supports (multi-)polygons and (multi-)linestrings of dimension 2.

Using a test dataset containing the state borders in Europe, preprocessing with ST_RemoveIrrelevantPointsForView() leads to the same rendering result as with the original geometries. Compared with ST_Intersection(), it returns about the same number of points but is up to 20 times faster which is, as far as our long-term experience goes, advantageous for real-time applications.

The code you can find as fork of ​https://github.com/postgis/postgis (master) here:

​https://github.com/gluser1357/postgis-fork/tree/remove_irrelevant_points_for_view

Please see also the initial discussion on postgis devel here:

​https://lists.osgeo.org/pipermail/postgis-devel/2024-March/030262.html

Thank you for reviews, hints and comments on this function or if there's something missing (e. g. more edge cases).

[gluser1357]

Here the Github pull request: ​https://github.com/postgis/postgis/pull/767

[mdavis]

Is this guaranteed to maintain polygonal validity? This should be stated in the docs.

[mdavis]

I suggest a slightly simpler function name, and one that uses terminology already in use. Perhaps ST_RemovePointsOutsideBBox?

[gluser1357]

Is this guaranteed to maintain polygonal validity? This should be stated in the docs

Currently, this function does not ensure polygonial validity. I added a warning in the docs (reference_editor.xml). Should I add it also at another location?

I suggest a slightly simpler function name, and one that uses terminology already in use. Perhaps ST_RemovePointsOutsideBBox?

I was really looking for another function name but I couldn't find a better one so far describing what the function does. Since some points are kept outside the box that are required to render the same result within the bbox your suggestion doesn't exactly hit the functionality. Other suggestions are welcome

[gluser1357]

What about ST_SimplifyForView, ST_SimplifyForBBox, ST_ReducePointsForView or ST_ReducePointsForBbox?