Thanks all for the quick reply and sorry for my late response. Thanks, Paul and Martin for clarifying the behavior to me. I'll see if I can change my workflow to handle these edge cases.
Also thanks to Darafei for the link to pprepair. I'll have a look at it, but I'm running Windows so it is a bit more complex to quickly test ;) Regards, Paul *Paul Meems * Release manager, configuration manager and forum moderator of MapWindow GIS. www.mapwindow.org Owner of MapWindow.nl - Support for Dutch speaking users. www.mapwindow.nl *The MapWindow GIS project has moved to GitHub <https://github.com/MapWindow>!* Download the latest MapWinGIS mapping engine. <https://github.com/MapWindow/MapWinGIS/releases> Download the latest MapWindow 5 open source desktop application. <https://github.com/MapWindow/MapWindow5/releases> Op wo 2 jan. 2019 om 18:26 schreef Martin Davis <mtncl...@gmail.com>: > As Paul says, this is expected behaviour, due to the fact that in general > constructed intersection vertices do not lie exactly on the line segments > which intersect. Furthermore, this can't be solved by using a coarser > precision model - that just makes the problem worse! > > So the only way to "solve" this is to ask a different question. One > possibility is to to process all or some of the input polygons to form a > properly noded coverage. Or, use a tolerance value in the overlaps > predicate, and accept that the output coverage will only be approximately > accurate. > > Both of these solutions will require some new algorithms in GEOS... > > On Wed, Jan 2, 2019 at 7:48 AM Paul Meems <bontepaar...@gmail.com> wrote: > >> Hi List, >> >> I'm creating irregular polygons and I don't want to let them overlap. >> So before adding the polygon to my list of 'good' polygons, I do an >> overlap check first. >> When the polygon overlaps with an existing polygon I do a clip difference >> and add the clipped polygon to my good list. >> >> Sometimes two polygons still overlap after a clip difference. >> >> I managed to extract two sets that barely overlap. The first set doesn't >> overlap anymore after clipping the second one is still overlapping. >> >> Set 1: >> shp = POLYGON ((259449.071118579 543868.469050065,259460.460699968 >> 543878.23006619,259463.245769758 543873.768560297,259455.578068317 >> 543860.876455946,259449.071118579 543868.469050065)) >> shp2 = POLYGON ((259463.243735243 543856.317227775,259458.0148573 >> 543864.973555723,259462.906856719 543873.198728218,259471.741696109 >> 543861.450443661,259463.243735243 543856.317227775)) >> shp3 (clipped result) = POLYGON ((259463.243735243 >> 543856.317227775,259458.014857301 543864.973555722,259462.906856719 >> 543873.198728217,259471.741696109 543861.450443661,259463.243735243 >> 543856.317227775)) >> >> Set 2: >> shp = POLYGON ((259073.014081524 544320.092508488,259085.267633063 >> 544321.677731439,259085.942168897 544320.308101652,259074.192475622 >> 544310.983687036,259073.014081524 544320.092508488)) >> shp2 = POLYGON ((259087.677538158 544333.393525226,259097.260135269 >> 544321.853428493,259090.546766392 544316.354731347,259079.984140336 >> 544327.005127152,259087.677538158 544333.393525226)) >> shp3 (clipped result) = POLYGON ((259087.677538158 >> 544333.393525226,259097.260135269 544321.853428493,259090.546766392 >> 544316.354731347,259085.267633064 544321.677731438,259085.267633063 >> 544321.677731439,259085.267633062 544321.677731439,259079.984140336 >> 544327.005127152,259087.677538158 544333.393525226)) >> >> I'm using C# with MapWinGIS to do the actions: >> if (shp.Overlaps(shp2)) >> { >> var shp3 = shp2.Clip(shp, tkClipOperation.clDifference); >> Assert.IsFalse(shp.Overlaps(shp3), "New shape still >> overlaps"); >> } >> >> MapWinGIS is using the GDAL v2.3.3 binaries from GisInternals which in >> turn is using geos-3.4 >> MapWinGIS is directly porting its functions to the GEOS functions: >> >> https://github.com/MapWindow/MapWinGIS/blob/master/src/COM%20classes/Shape.cpp#L1194 >> >> https://github.com/MapWindow/MapWinGIS/blob/master/src/COM%20classes/Shape.cpp#L1302 >> >> Before I report this as a defect I want to know if my workflow and >> expectations are correct. >> >> Thanks, >> >> Paul >> _______________________________________________ >> geos-devel mailing list >> geos-devel@lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/geos-devel > > _______________________________________________ > geos-devel mailing list > geos-devel@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/geos-devel
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