ST_SubDivide garden crasher on malformed polygon and linestring

[robe]

I didn't even think it was possible to create a geometry like this. You learn so much from robot monkeys

SELECT ST_SubDivide(ST_GeomFromText('POLYGON((1 2,1 2,1 2,1 2))'), 2);

SELECT ST_SubDivide(ST_GeomFromText('LINESTRING(1 2,1 2,1 2,1 2)'), 2);

pramsey you've got to try harder to out smart monkeys

[robe]

forgot my install was runnning on PostgreSQL 9.5 dev (about 3 day old install)

POSTGIS="2.2.0dev r13566" GEOS="3.5.0dev-CAPI-1.9.0 r4034" PROJ="Rel. 4.8.0, 6 March 2012" LIBXML="2.7.8" LIBJSON="0.12"

[pramsey]

This is almost certainly a GEOS crasher, but I'll confirm in gdb.

[pramsey]

It's not a GEOS crasher, it's a problem in the recursion w/ the zero-size input.

[pramsey]

Fixed at r13576

[robe]

Not so fast - monkey can still crash your code at r13578 with this:

SELECT ST_SubDivide(ST_GeomFromText('POLYGON((1 2,1 2,1 2,1 2,3 2,1 2))'),2);

[pramsey]

Your case is "fixed" at r13580, however it's not a perfect fix. It won't crash anymore, no matter what you do, even if you pack your object with enough repeated points to force another infinite recursion because I put in a recursion stopper. If you do try that you'll find the output is "wrong" as the portion of the object with the repeated points just disappears into the aether. The overhead in trying to catch that case and do the "right" thing (which is probably to remove the repeated points) is just too high. Another possibility would be to stuff the whole input object through the repeated points remover right at the start; not sure if we want to do that. My proximate fix, to avoid dropping your slightly repeating input was just to increase the minimum number of vertices we'd guarantee, since my mind boggled at what it meant to ask the function "only return polygons with no more than two vertices in them".

[robe]

I see what ya mean squeallie is happy but doc examples don't work.

If it's hard, I suppose I could change the doc examples and we just put a notice that can't go below 16 or whatever we decide.

​http://postgis.net/docs/manual-dev/ST_Subdivide.html