Hi,
Currently, the help page of PostGIS's ST_ReducePrecision command more or
less suggests that ST_ReducePrecision can be used as kind of "drop-in"
replacement of ST_MakeValid. The actual text reads:
/"Returns a valid geometry with all points rounded to the provided grid
tolerance, and features below the tolerance removed.
Unlike ST_SnapToGrid the returned geometry will be valid, with no ring
self-intersections or collapsed components./
/Precision reduction can be used to: /
*
/match coordinate precision to the data accuracy /
*
/reduce the number of coordinates needed to represent a geometry /
*
/ensure valid geometry output to formats which use lower precision
(e.g. text formats such as WKT, GeoJSON or KML when the number of
output decimal places is limited). /
*
/export valid geometry to systems which use lower or limited
precision (e.g. SDE, Oracle tolerance value)"/
However, a first test replacing:
ST_CollectionExtract(ST_MakeValid(<SOME OTHER GENERALIZATION CODE>),3)
with:
ST_ReducePrecision(<SOME OTHER GENERALIZATION CODE>),<GRID SIZE>)
failed on some geometries with a processing error.
Replacing the first try with:
ST_ReducePrecision(ST_CollectionExtract(ST_MakeValid(<SOME OTHER
GENERALIZATION CODE>),3),<GRID SIZE>)
did succeed.
This suggest to me that the help page should actually read something like:
/"Returns a geometry with all points rounded to the provided grid
tolerance, and features below the tolerance removed.
Unlike ST_SnapToGrid the returned geometry is guaranteed to be valid,
with no ring self-intersections or collapsed components, if the input
geometry itself is valid. If the input geometry is invalid, there is no
guarantee the output will be valid. Use ST_MakeValid to ensure the input
is valid before running this command if the input data may contain
invalid geometries."/
Is my interpretation of how//ST_ReducePrecision handles validity as
reflected by this suggested updated help text correct?/
/
Marco/
/
