Changes between Initial Version and Version 1 of Ticket #253


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Timestamp:
May 19, 2009, 9:18:20 AM (15 years ago)
Author:
mloskot
Comment:

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  • Ticket #253 – Description

    initial v1  
    22
    33I'm very new to GEOS (< 1 day), but I'm puzzled by what I think is a strange bug.
     4
    45Being particularly interested in the GEOSUnionCascaded() function to merge large sets (>50,000) of overlapping polygons, altering my dataset manually to avoid this bug(?) is not an option.
    56
    67I have narrowed down the problem to the following multipolygon, which represents a rectangle inside an octagon (see http://homes.esat.kuleuven.be/~wvereeck/rect_inside_oct.png)
    78
     9{{{
    810MULTIPOLYGON(((12.26 18.46, 11.76 18.46, 11.54 18.24, 11.54 17.34, 11.76 17.12, 12.26 17.12, 12.48 17.34, 12.48 18.24, 12.26 18.46)),((12.37 18.35, 11.65 18.35, 11.65 17.23, 12.37 17.23, 12.37 18.35)))
     11}}}
    912
    1013I am using the c-interface. Running the GEOSisValid() test on this polygon set results in:
     14
     15{{{
    1116   NOTICE: Self-intersection at or near point 12.37 18.35
     17}}}
     18
    1219Also, GEOSUnionCascaded() accordingly fails with:
    13    ERROR: TopologyException: found non-noded intersection between 11.65 etc...
     20
     21{{{
     22   ERROR: TopologyException: found non-noded intersection between 11.65
     23}}}
     24
     25etc.
    1426
    1527However, when I slightly offset the x-position (+1e-8) of the two top vertices of the rectangle, everything works like a charm (i.e. GEOSisValid returns 'true' and GEOSUnionCascaded produces the correct output polygon):
    1628
     29{{{
    1730MULTIPOLYGON(((12.26 18.46, 11.76 18.46, 11.54 18.24, 11.54 17.34, 11.76 17.12, 12.26 17.12, 12.48 17.34, 12.48 18.24, 12.26 18.46)), ((12.37000001 18.35, 11.65000001 18.35, 11.65 17.23, 12.37 17.23, 12.37000001 18.35)))
     31}}}
    1832
    1933I apologize if I'm too much in a hurry here and should start to learn more about geos before submitting a complaint :) At least I hope this is the right place for this problem.
    … …  
    2337
    2438FWIW, I'm using geos-3.1.0.tar.bz2 (2009/03/17), libgeos-3.1.0 and Ubuntu 8.04.2 (x86-64) with a 2.6.24-23-generic kernel.
    25