Hi Gerd Looking at your example, the end point of the line is inside the area, but only by about 1 metre. This is the within the tolerance of a point being considered ON a line with the current algo/EPS. All the other points on the line ON or OUT of the area. Changing the tolerance and/or the type of distance calculation might change the overall answer to be IN & ON & OUT, but consider if the end point of the line was exactly on the edge; the answer would be wrong. The problem really is in the line following shape edge algo that should spot that the line has diverged from the edge into the area. I haven't looked in detail yet at Joris's failures, but did you notice if they were of this pattern, where the line spans the area in one bound? In your change to isPointInShape, you've lost the general case (line not horizontal or vertical): distSqrd = lonDifSqrd * latDifSqrd / (lonDifSqrd + latDifSqrd); Regarding the comment about a small error area on the outside of the polygon vertex where a point will report ON but shouldn't - this area is very small but does exist and so the the comment is valid. Ticker On Wed, 2020-05-20 at 08:53 +0000, Gerd Petermann wrote:
Hi Ticker
the problem is in mkgmap. I can reproduce it with the attached simple example.
I think the bug is in the distance calculation in isPointInShape(), see attached patch. It returned ON for a point which is clearly inside. I've also changed the way how test points are calculated so that the rounding tolerances are less likely to produce a problem. I don't understand the meaning of the comment // there is a small area between the square EPS_HP*2 and the circle within, where, if polygon vertex and // segments are the other side, it might still be calculated as ON. so maybe my patch makes things worse in other situations? My understanding is that we can use a² + b² = c² , so maybe the comment can be removed as well?
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Joris Bo <jorisbo@hotmail.com> Gesendet: Dienstag, 19. Mai 2020 21:12 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] Explanation of the is_in function
Hi Ticker,
Thx for the update, off course no problem.
Gr Joris
-----Oorspronkelijk bericht----- Van: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> Namens Ticker Berkin Verzonden: dinsdag 19 mei 2020 18:57 Aan: Development list for mkgmap <mkgmap-dev@lists.mkgmap.org.uk> Onderwerp: Re: [mkgmap-dev] Explanation of the is_in function
Hi Joris
I can't do anything in the next few days to investigate this but I'll have a look when I can.
Ticker
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