[geos-devel] Union of linestrings

[Mateusz Loskot]

On 1 March 2016 at 16:06, Sandro Santilli <strk at keybit.net> wrote:
> On Tue, Mar 01, 2016 at 03:41:37PM +0100, Mateusz Loskot wrote:
>> On 1 March 2016 at 15:09, Sandro Santilli <strk at keybit.net> wrote:
>> > On Tue, Mar 01, 2016 at 02:52:32PM +0100, Mateusz Loskot wrote:
>> >
>> >> What about constructing a single LineString from connected
>> >> segments, instead of a MultiLineString?
>> >
>> > LineMerge operation, aka GEOSLineMerge_r in C-API.
>>
>> Right, makes sense.
>>
>> So, by design, union of connected segments always yields MultiLineString.
>> Safe assumption?
>
> I think this is the current case, yes.
>
> The union operation makes no effort to drop nodes of degree 2
> (having just 2 edges connected) from the built topology.

Good. The test I have added [1] documents this behaviour,
at least for LineString geometries.

[1] https://trac.osgeo.org/geos/browser/trunk/tests/unit/operation/overlay/OverlayOpUnionTest.cpp?rev=4153#L61

Best regards,
-- 
Mateusz Łoskot, http://mateusz.loskot.net