[postgis-tickets] [PostGIS] #5148: ST_Clip ERROR: rt_raster_from_two_rasters: The two rasters provided do not have the same alignment

[PostGIS]

#5148: ST_Clip ERROR: rt_raster_from_two_rasters: The two rasters provided do not
have the same alignment
----------------------+---------------------------
 Reporter:  sergeish  |      Owner:  robe
     Type:  defect    |     Status:  new
 Priority:  medium    |  Milestone:  PostGIS 3.3.0
Component:  raster    |    Version:  master
 Keywords:            |
----------------------+---------------------------
 Called from `RASTER_clip` (`ST_Clip`), `rt_raster_gdal_rasterize` can
 produce mask raster that is not aligned with input raster.

 In our case, the input geometry's (h3 index polygon) max. Y coordinate
 just happens to be within `FLT_EPSILON` distance from input raster Y
 coordinate.
 This causes alignment step in `rt_raster_gdal_rasterize` to be skipped
 [https://github.com/postgis/postgis/blob/9c4a85d2aadacb008489630f14168958b770a065/raster/rt_core/rt_raster.c#L3075
 rt_raster.c:3075]

 Later in `RASTER_clip -> rt_raster_from_two_rasters ->
 rt_raster_same_alignment -> rt_raster_geopoint_to_cell`
 [https://github.com/postgis/postgis/blob/9c4a85d2aadacb008489630f14168958b770a065/raster/rt_core/rt_spatial_relationship.c#L91
 rt_rpatial_relationship.c:91] the difference get magnified by `1/scale`
 (scale = `8.3333333333338033e-05`) and position of upper left corner
 relative to raster becomes (0, -1)
 [https://github.com/postgis/postgis/blob/9c4a85d2aadacb008489630f14168958b770a065/raster/rt_core/rt_raster.c#L831
 rt_raster.c:831] so alignment check correctly fails.

 {{{
 # SELECT ST_Clip(
   ST_AsRaster(
     ST_GeomFromText('POLYGON((-83.50933333333333
 29.978666666666665,-83.488 29.978666666666665,-83.488
 29.95733333333333,-83.50933333333333 29.95733333333333,-83.50933333333333
 29.978666666666665))'),
 256, 256),
   ST_GeomFromText('POLYGON((-83.50907828753448
 29.968993886572754,-83.50444815780213
 29.971082725355338,-83.50415647331064 29.97591893624371,-83.50849527658693
 29.978666590716937,-83.51312588106222
 29.976577808850404,-83.51341720749126 29.97174131559702,-83.50907828753448
 29.968993886572754))'));
 ERROR:  rt_raster_from_two_rasters: The two rasters provided do not have
 the same alignment
 CONTEXT:  PL/pgSQL function st_clip(raster,integer[],geometry,double
 precision[],boolean) line 8 at RETURN
 SQL function "st_clip" statement 1
 }}}

 Possible solutions for fixing alignment check in
 `rt_raster_gdal_rasterize`
 [https://github.com/postgis/postgis/blob/9c4a85d2aadacb008489630f14168958b770a065/raster/rt_core/rt_raster.c#L3075
 rt_raster.c:3075]:
 * take scale into account when checking if raster is already aligned, like
 (`FLT_EQ(fabs(grid_yw - extent.UpperLestY) / scale, 0.0)` for `scale <
 1.0`);
 * replace `FLT_EQ` with `DBL_EQ`.

 Is there a reason for using `FLT_EQ` for comparing doubles throughout
 `raster` code? This issue will be resolved as a special case if `DBL_EQ`
 is used instead.

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5148>
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