[geos-devel] OverlayOp JTS port

Wed Sep 17 17:33:55 EDT 2008

I can confirm - if GEOS is doing something with computing new Z-values 
this is something which is NOT in JTS.  I vaguely recollect that this is 
something which Sandro added.

Obe, Regina wrote:
> Okay I did a quick union run of a 3 d geometry in PostGIS and it
> apparently does do something with the z index
>
> SELECT ST_AsEWKT(ST_Union(ST_MakePoint(x,y,z)))
> FROM generate_series(1,5) x
> 	CROSS JOIN generate_series(2,10) y
> 	CROSS JOIN generate_series(1,10) z;
>
> yields
> MULTIPOINT(1 2 9.001953125,1 3 9.001953125,1 4 9.001953125,1 5
> 9.001953125,1 6 9.001953125,1 7 9.001953125,1 8 9.001953125,1 9
> 9.001953125,1 10 9.001953125,2 2 9.001953125,2 3 9.001953125,2 4
> 9.001953125,2 5 9.001953125,2 6 9.001953125,2 7 9.001953125,2 8
> 9.001953125,2 9 9.001953125,2 10 9.001953125,3 2 9.001953125,3 3
> 9.001953125,3 4 9.001953125,3 5 9.001953125,3 6 9.001953125,3 7
> 9.001953125,3 8 9.001953125,3 9 9.001953125,3 10 9.001953125,4 2
> 9.001953125,4 3 9.001953125,4 4 9.001953125,4 5 9.001953125,4 6
> 9.001953125,4 7 9.001953125,4 8 9.001953125,4 9 9.001953125,4 10
> 9.001953125,5 2 9.001953125,5 3 9.001953125,5 4 9.001953125,5 5
> 9.001953125,5 6 9.001953125,5 7 9.001953125,5 8 9.001953125,5 9
> 9.001953125,5 10 9.001953125)
>
> Running the same exercise in OpenJump and looking at the output of GML,
> WKT, CL I don't get a Z-axis.
>
> I can't tell if its just that the z is not supported in those formats or
> if its just because in JTS the z axis is thrown out.  Looking at the JTS
> code, I have no reason to believe its doing anything with z.
>
> I presume the GEOS elevationMatrix->elevate(resultGeom) is responsible
> for this.
>
> The question I have is - isn't this hmm wrong - I suppose we can say its
> fuzzily right.
>
> Thanks,
> Regina
>
>
>
> -----Original Message-----
> From: geos-devel-bounces at lists.osgeo.org
> [mailto:geos-devel-bounces at lists.osgeo.org] On Behalf Of Martin Davis
> Sent: Wednesday, September 17, 2008 2:24 PM
> To: GEOS Development List
> Subject: Re: [geos-devel] OverlayOp JTS port
>
> The original plan for GEOS was that it would track JTS 100%.  This was 
> to simplify porting new functionality as it is added to JTS.  However, 
> at one point I think Sandro did some extra work on trying to improve 
> GEOS robustness.  This is probably where the checkObviouslyWrongResult 
> came from.  After this was done, JTS caught up - so this method may not 
> be needed any more.
>
>
>
> Obe, Regina wrote:
>   
>> I apologize for the barrage of questions.  As far as I can tell the
>> OverlayOp.cpp is vintage JTS 1.7 (which I think is same as the JTS 1.9
>>     
>
>   
>> for this class)
>>
>> except it has the additional calls of
>>
>> checkObviouslyWrongResult() - which most of that code looks like it 
>> would never
>> be called because of the #ifdefs except for the 
>>
>> assert(resultGeom);
>> UNREFERENCED_PARAMETER(opCode); (have no clue what this does)
>>
>> and also a
>> elevationMatrix->elevate(resultGeom);
>>
>> which looks like will get called since USE_ELEVATION_MATRIX 1.
>>
>> Is the elevationMatrix designed to deal with 3d geometries?  Didn't 
>> realize
>> Union actually works with those, but then I never tried it with 3d.
>>
>> So I'm a little puzzled why these 2 extra function calls since I 
>> always thought
>> GEOS was at best on par with JTS?
>>
>> Thanks,
>> Regina
>>
>> -----Original Message-----
>> From: geos-devel-bounces at lists.osgeo.org on behalf of Obe, Regina
>> Sent: Wed 9/17/2008 9:26 AM
>> To: GEOS Development List
>> Subject: [geos-devel] OverlayOp JTS port
>>
>> I'm looking at the operation.overlay.OverlayOp in geos trunk
>>
>> In the header it says
>> Last port: operation/overlay/OverlayOp.java rev. 1.23
>>
>> But I don't believe this to be right since when I compare the
>> computeOverlay methods
>> against 1.2 and 1.3 versions of JTS codebase, it has an additional
>> EdgeNodingValidator check which wasn't introduced until later versions
>> of JTS.
>>
>> So I'm wondering is the OverlayOp.cpp a mix of JTS versions or is the
>> comment above just plain wrong.
>>
>> It also has a checkObviouslyWrongResult() check at the end of
>> computerOverlay which I haven't figured out which version that was
>> introduced in JTS (its not in 1.2,1.3, or 1.9).  Is this a GEOS
>>     
> specific
>   
>> check that has no JTS equivalent?
>>
>> Thanks,
>> Regina
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022