[postgis-tickets] [PostGIS] #4184: Completely different geometry after St_MakeValid

[PostGIS]

#4184: Completely different geometry after St_MakeValid
------------------------+---------------------------
 Reporter:  Algunenano  |      Owner:  Algunenano
     Type:  defect      |     Status:  assigned
 Priority:  medium      |  Milestone:  PostGIS 2.4.6
Component:  postgis     |    Version:  2.4.x
 Keywords:              |
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 I start with the following geometry from the NYC mnmappluto dataset:
 {{{
 SRID=3857;MULTIPOLYGON(((-8231365.02893734
 4980355.83678553,-8231366.94866817 4980350.2976052,-8231368.82883367
 4980344.52250402,-8231370.96255986 4980333.47364302,-8231372.09200747
 4980327.69798564,-8231372.84505222 4980323.68014243,-8231374.2255656
 4980316.77455645,-8231375.10554947 4980309.86865218,-8231380.6311111
 4980275.9676398,-8231394.82332406 4980186.31880185,-8231394.8569833
 4980133.57928934,-8231367.43081065 4979982.17443372,-8231372.85765532
 4979985.17751813,-8231395.25669799 4980132.93828551,-8231396.69199339
 4980227.59327083,-8231377.30092207 4980340.77515211,-8231368.35061694
 4980357.62467295,-8231365.02893734 4980355.83678553)))
 }}}

 As when I simplify the geometry for rendering it ends up being invalid I
 force validation with St_MakeValid:
 {{{
 Select
 St_AsEWKT(St_MakeValid(ST_Simplify(ST_RemoveRepeatedPoints('SRID=3857;MULTIPOLYGON(((-8231365.02893734
 4980355.83678553,-8231366.94866817 4980350.2976052,-8231368.82883367
 4980344.52250402,-8231370.96255986 4980333.47364302,-8231372.09200747
 4980327.69798564,-8231372.84505222 4980323.68014243,-8231374.2255656
 4980316.77455645,-8231375.10554947 4980309.86865218,-8231380.6311111
 4980275.9676398,-8231394.82332406 4980186.31880185,-8231394.8569833
 4980133.57928934,-8231367.43081065 4979982.17443372,-8231372.85765532
 4979985.17751813,-8231395.25669799 4980132.93828551,-8231396.69199339
 4980227.59327083,-8231377.30092207 4980340.77515211,-8231368.35061694
 4980357.62467295,-8231365.02893734 4980355.83678553)))'::geometry,
 19.109257221221924), 19.109257221221924, true)));
 }}}

 The end result is nowhere near the original input:
 https://user-
 images.githubusercontent.com/664253/45769751-d27aeb80-bc40-11e8-9c12-dd63e202b0df.png

 In purple the original geometry, in orange (and much bigger than the
 screenshot) the final geometry.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4184>
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