[postgis-tickets] [PostGIS] #4161: St_AsMVTGeom: Shortcut geometries smaller than the tolerance

[PostGIS]

#4161: St_AsMVTGeom: Shortcut geometries smaller than the tolerance
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 Reporter:  Algunenano   |      Owner:  Algunenano
     Type:  enhancement  |     Status:  assigned
 Priority:  medium       |  Milestone:  PostGIS 3.0.0
Component:  postgis      |    Version:  trunk
 Keywords:               |
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 St_AsMVTGeom drops geometries when they get too small after snapping them
 to the final grid. With this PR we now try to drop those geometries right
 away so they don't have to go through
 lwgeom_remove_repeated_points_in_place + lwgeom_simplify_in_place +
 lwgeom_clip_by_rect + lwgeom_affine + lwgeom_grid_in_place unnecessarily.

 This doesn't have any noticeable performance impact in point datasets or
 when the geometries are bigger* than the tolerance ( < ±5% performance
 difference testing whole tile generation), but it's a nice improvement for
 low zoom tiles (bigger tolerance, more geometries dropped), almost halving
 some of the timings.

 *Bigger as in, it's bounding box max size is bigger than the tolerance,
 which is set to 1/2 * tile_size / tile_extent.

 This PR also means a small additional change that can be considered both a
 drawback or an improvement: Due to how the simplification functions work,
 some super small geometries could go through the simplification process if
 they were between grid borders; so for a set of geometries with the same
 shape and size, some might appear and some don't depending on their
 position in the grid. With this PR this should be more consistent.

 PR (WIP): https://github.com/postgis/postgis/pull/288

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4161>
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