Question

I was having problems while intersecting two geometries, getting a TopologyException probably due to a rounding error during the operation, then I read this fix and tried a buffer(0) on both input geometries, but still without success. Then I tried geo.buffer(1).buffer(-1) and it worked.

Will these geometries be equivalent to the original ones?

Answer 1

I don’t know anything about JTS, but it can’t be true in general.

Assume you have two shapes:

 XXX      XXX
 X X      XXX
 XXX      XXX

From my understanding a buffer(1) on both would result in roughly this:

XXXXX    XXXXX
XXXXX    XXXXX
XXXXX    XXXXX
XXXXX    XXXXX
XXXXX    XXXXX

Now buffer(-1) won’t be able to produce two different results from those two shapes.

Effectively a buffer() operation looses information, so it can’t be undone without re-adding that information from somewhere else.