[geos-devel] Geometry/Rectangle Intersection, line merging ?

[Mika Heiskanen]

On 09/09/2014 01:48 PM, Sandro Santilli wrote:
> RE: rectangle intersection (#699)
>
> I've plugged the leak and compared the result of Geometry::intersection()
> and RectangleIntersection. One difference is about the linemerge operation
> happening in the RectangleIntersection class, that is a line going outside
> and then back inside the clipping rectangle gets merged by
> RectangleIntersection while it is not by standard intersection.
>
> The tests you provided expect the merging to happen, so if I drop the merging
> those tests are going to fail. What's the rationale for that additional
> operation ?

I assume you are referring to these comments:

  * Sample clip with a rectangle 0,0 --> 10,10 without reconnecting:
  *
  *   Input:   POLYGON ((5 10,0 0,10 0,5 10))
  *   Output:  MULTILINESTRING ((5 10,0 0),(10 0,5 10))
  *   Desired: LINESTRING (10 0,5 10,0 0)

If you recall, we wrote the algorithm for rendering. In this case if we
do not reconnect the two linestrings line-join behaviour will be broken
during rendering.

Regards,

Mika Heiskanen / FMI