[geos-devel] Re: Polygonizer bug ?

[strk]

On Mon, Jun 21, 2010 at 09:13:16AM -0700, Martin Davis wrote:
> strk,
> 
> The JTS Developer's Guide is a bit confusing.  The geometry given in the 
> example is NOT the geometry depicted in the illustration. (This is  a 
> doc bug - but I"m not sure if and when I can fix it).
> 
> When I run the geometry below in JTS I get:
> 
> Polygons:
> GEOMETRYCOLLECTION (
>  POLYGON ((189 98, 83 187, 185 221, 325 168, 189 98)),
>  POLYGON ((185 221, 88 275, 180 316, 292 281, 185 221)))
> 
> Dangles:
> MULTILINESTRING ((185 221, 100 100),
>  (0 0, 10 10))
> 
> I believe this is the expected result.

Uhm, that's w/out self-noding, right ?

--strk;


> 
> Hope that helps
> 
> Martin
> 
> strk wrote:
> >Martin, I'm adding a testcase for the Polygonizer using example from :
> >"JTS Developer's Guide, Chapter 6 - Polygonization"
> >
> >Here's the input, represented as a collection:
> >
> >GEOMETRYCOLLECTION(
> >            LINESTRING(0 0, 10 10),
> >            LINESTRING(185 221, 100 100),
> >            LINESTRING(185 221, 88 275, 180 316),
> >            LINESTRING(185 221, 292 281, 180 316),
> >            LINESTRING(189 98, 83 187, 185 221),
> >            LINESTRING(189 98, 325 168, 185 221))
> >)
> >
> >When passing it into the Polygonizer class I get
> >2 rings, no cut or invalid edges and 3 dangles.                            
> >Also notable is that of the 3 dangles, 2 are identical
> >and specificall are the isolated edge (first geometry
> >in the collection).
> >
> >The example in the guide suggests the rings should
> >be 3 instead, and that there should be one cut
> >edge (represented in blue) and 2 dangles
> >the red ones.
> >
> >Does it sound as a bug in GEOS or does JTS give the
> >same results ?
> >
> >Note that forcing proper noding using the union trick
> >does give the 3 expected rings, but still lacks the
> >cut edge and duplicates the dangle.
> >
> >Thanks in advance.
> >
> >--strk;
> >
> >  ()   Free GIS & Flash consultant/developer
> >  /\   http://strk.keybit.net/services.html
> >  
> 
> -- 
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022

-- 

  ()   Free GIS & Flash consultant/developer
  /\   http://strk.keybit.net/services.html