Changes between Initial Version and Version 1 of Ticket #5974, comment 3


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Timestamp:
May 22, 2015, 12:54:49 PM (9 years ago)
Author:
Even Rouault

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  • Ticket #5974, comment 3

    initial v1  
    1 Closer analysis show that one of the ring has clockwise orientation, while the other one has conter-clockwise orientation, so in shapefile convention, this means that one is the inner ring of the other one. So the shape, as in the .shp, is not built as a multipolygon. That's the blocking issue.
     1Closer analysis shows that one of the rings has clockwise orientation, while the other one has conter-clockwise orientation, so in shapefile convention, this means that one is the inner ring of the other one (clockwise = outer ring, counter clocksie = inner ring). So the shape, as in the .shp, is not built as a multipolygon. That's the blocking issue.
    22
    33I'd note that the export code of the shapefile driver in its topological analysis to properly turn rings into clockwise or counter-clockwise will correct it (if you do: ogr2ogr out.shp polygon.shp). So this shape hasn't been written with OGR. With that corrected shapefile, the spatial intersection works correctly (even if GEOS still protest about self-intersection when running IsValidReason())