Hi Gerd The logic of ShapeSplitter is based on polygons not self-intersecting and this is what makes it fast. OSM polygons are not self-intersecting unless they are in error. MultiPolygon processing should be stopped from generate them; there is no need. Once they occur and have to be handled later in the processing it will add complications to splitting and probably to merging. ShapeSplitter doesn't make any attempt to detect self-intersection and it won't notice many occurrences of it; it depending on where the cut -line is and if signs of areas make sense. Often the result will be "rubbish-out" for self-intersecting input. This means it is unreliable to catch problems when it does detect them and use some alternate algorithm. Although Garmin might render simple figure-of-8 in what seems like a sensible way, what happens when there is [multiple] overlap etc. Some polygon rendering algorithms alternate shape/not-shape for each additional overlap. Do all other programs that display Garmin .img do the same thing? I'd rather avoid this question and never cause self -intersection. Ticker On Tue, 2021-06-08 at 07:43 +0000, Gerd Petermann wrote:
Hi Ticker,
my understanding is that Garmin software has no problems with this kind of self-intersection. In this particular case the problem could be solved in method MultipolygonRelation.joinWays(), as 4 ways are connected at the same point, but self-intersecting shapes are also possible as simple ways. While they are wrong for OSM they should be allowed for MapShape since Garmin allows them, too.
A possible way to fix those shapes is something like this: Path2D.Double path = Java2DConverter.createPath2D(polygonPoints); path.setWindingRule(Path2D.WIND_EVEN_ODD); List<List<Coord>> shapes = Java2DConverter.areaToShapes(new java.awt.geom.Area(path)); So, maybe ShapeSplitter could do this with the input shape in case of error and try again with shapes?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap@jagIT.co.uk> Gesendet: Dienstag, 8. Juni 2021 08:54 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] low-res-opt branch: error message from ShapeSplitter for self-intersecting multipolygon
Hi Gerd
The shape is a figure-of-8 so shapesSplitter needs to give some error.
If this isn't an original OSM shape, it points to some problem with earlier processing, probably shape-merging. Although it might render (could be device dependent), further processing (eg overview merging) could come to grief.
Ticker
On 07/06/2021 10:24, Gerd Petermann wrote:
Hi Ticker,
okay, no problem, I'll work on the faster-mp branch in the mean time Maybe I'll merge it first into the low-res-opt branch.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap@jagit.co.uk> Gesendet: Montag, 7. Juni 2021 11:23 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] low-res-opt branch: error message from ShapeSplitter for self-intersecting multipolygon
Hi Gerd
The shape I'm getting in my build has a major problem with a twist between the 2 parts. I'm having trouble reconciling it with the OSM map. I've attached the original shape trace.
I agree that some of the messages do need tweaking, but, in this cases there is a significant problem.
I'll consider the types of messages etc in the new version I'm working on.
I'm away for a few days and won't be able to do much remotely.
Ticker
On Mon, 2021-06-07 at 07:22 +0000, Gerd Petermann wrote:
Hi Ticker,
please check https://files.mkgmap.org.uk/download/512/63240024.o5m with (unpatched) r4756 and these options --generate -sea=multipolygon,floodblocker --preserve-element-order --order -by -decreasing-area --allow-reverse-merge
Produces an error message SCHWERWIEGEND (ShapeSplitter): e:\osm_out_work\norway\20210511_095323\63240024.o5m: Vertical split 36691968 failed on shape at http://www.openstreetmap.org/?mlat=65.979056&mlon=12.308790&zoom= 17 P ossibly a self-intersecting polygon for this invalid multipolygon : https://www.openstreetmap.org/relation/5294624
The result doesn't look wrong, so I think there should either be no error message or we need code to remove those self-intersections or ignore invalid MP like that?
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