[postgis-tickets] [PostGIS] #4636: ST_Subdivide degrade data

[PostGIS]

#4636: ST_Subdivide degrade data
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  Reporter:  sirsosp  |      Owner:  strk
      Type:  defect   |     Status:  assigned
  Priority:  high     |  Milestone:  PostGIS 3.1.0
 Component:  postgis  |    Version:  2.5.x
Resolution:           |   Keywords:
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Changes (by strk):

 * status:  new => assigned
 * owner:  pramsey => strk


Comment:

 I've enabled debugging of BinaryOp in GEOS to find out what was going on
 and I found that in one of the recursive intersection cases all the
 heuristics fail until geometry precision reduction step is entered. The
 precision reduction starts with a grid of 1e-16 and grows the grid by 10
 everytime the intersection fails with a topology exception. The biggest
 grid eventually succeeding is 1, which is visible in the output as a grid.

 This also explains the time difference, as it basically takes 16 attempts
 only in the precision reduction step, not counting earlier attempts with
 snapping and common-bits removal...

 More stats: precision reduction is engaged 26 times. Of these, 2 times we
 have to get down to 1 as a grid size (I guess this is due to using the
 same middle-line for the binary subdivision of the same input polygon).
 All the other 24 cases work at the very first 1e-16 grid size.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4636#comment:11>
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