[gdal-dev] Proposed changed to solve inconsistant spatial filtering for null or empty geometries

[Even Rouault]

Hi,

Nyall Dawson pointed to me in 
https://github.com/qgis/QGIS/pull/5501#issuecomment-340934947 about a weird behaviour 
of OGR spatial filtering regarding null and empty geometries.

To make it concrete, consider the following CSV file

id,WKT
1,"POLYGON EMPTY"
2,
3,"POLYGON ((0 0,0 1,1 1,0 0))"


$ ogrinfo test.csv -al -spat 0 0 1 1 -q

Layer name: test
OGRFeature(test):1
  id (String) = 1
  WKT (String) = POLYGON EMPTY
  POLYGON EMPTY

OGRFeature(test):2
  id (String) = 2
  WKT (String) = 

OGRFeature(test):3
  id (String) = 3
  WKT (String) = POLYGON ((0 0,0 1,1 1,0 0))
  POLYGON ((0 0,0 1,1 1,0 0))

$ ogrinfo test.csv -al -spat 1 1 2 2 -q

Layer name: test
OGRFeature(test):2
  id (String) = 2
  WKT (String) = 

OGRFeature(test):3
  id (String) = 3
  WKT (String) = POLYGON ((0 0,0 1,1 1,0 0))
  POLYGON ((0 0,0 1,1 1,0 0))

So features with null geometries (FID 2) are always selected. And for a feature with an empty 
geometry (FID 1), it is selected by the -spat 0 0 1 1 filter since internally the envelope of 
POLYGON EMPTY is computed as xmin=xmax=ymin=ymax=0, but not by -spat 1 1 2 2

If ingesting this file into PostGIS and doing the same test, we get:

$ ogrinfo pg:dbname=autotest test -spat 0 0 1 1 -q

Layer name: test
OGRFeature(test):3
  id (String) = 3
  wkt (String) = POLYGON ((0 0,0 1,1 1,0 0))
  POLYGON ((0 0,0 1,1 1,0 0))

$ ogrinfo pg:dbname=autotest test -spat 1 1 2 2 -q

Layer name: test
OGRFeature(test):3
  id (String) = 3
  wkt (String) = POLYGON ((0 0,0 1,1 1,0 0))
  POLYGON ((0 0,0 1,1 1,0 0))

So null or empty geometries are never selected when a spatial filter is set. This last behaviour 
seems to be the most logical for me, and I'd propose we adopt it for non-SQL based drivers 
as well.
(note: the current behaviour dates back to the initial introduction of spatial filtering in OGR 
per https://trac.osgeo.org/gdal/changeset/7191 , 13 years ago )

Any thought ?

Even

-- 
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http://www.spatialys.com
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