[postgis-tickets] [PostGIS] #3929: Unexpected rounding from ST_SnapToGrid

[PostGIS]

#3929: Unexpected rounding from ST_SnapToGrid
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 Reporter:  michaudm  |      Owner:  pramsey
     Type:  defect    |     Status:  new
 Priority:  medium    |  Milestone:  PostGIS 2.4.2
Component:  postgis   |    Version:  2.4.x
 Keywords:            |
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 I would expect that
 ST_Equals(ST_GeomFromText('POINT(311.4 0)'),
 ST_SnapToGrid(ST_GeomFromText('POINT(311.4 0)'), 0.1));

 but it returns FALSE;

 The x value returned by snaprounding "seems" to be as close as possible
 from 311.4
 SELECT ST_X(ST_GeomFromText('POINT(0 311.4)'));
 -> display 311.4

 But while
 SELECT ST_X(ST_GeomFromText('POINT(311.4 0)'))-311.4
 display 0
 SELECT ST_X(ST_SnapToGrid(ST_GeomFromText('POINT(311.4 0)'), 0.1))-311.4
 display 5.6843418860808e-014

 x-value is not the same after snap rounding.

 My use case was :
 I want to check that all my coordinates are decimetric.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3929>
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