[mkgmap-dev] Gaps in surfaces

Fri Sep 29 07:57:36 BST 2023

Hi all,

I've found out that this problem is caused by a flaw in the "high precision" code. Under special conditions, two points with almost identical coordinates are internally represented
with very different values. There is a possible overflow in the delta values, the value +32 should not occur as it cannot be represented with 6 bits, but the calculations produce this value.
I think I have an ugly fix for this but the resulting map still shows (smaller) gaps and a unit test needs corrections, so there is more to do.
Attached is a patch that checks for this overflow. Work in progress and maybe causes trouble in other areas, e.g. in South America where we have negative lat/lon values.

@Ticker: The unit test für LineClipperTest fails. I am not sure if only the test has to be changed (how) or if the code in LineClipper can be improved. I seem to remember that you suggested to use
the code in ShapeSplitter instead.

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Gerd Petermann <gpetermann_muenchen at hotmail.com>
Gesendet: Dienstag, 26. September 2023 19:58
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] Gaps in surfaces

Hi Michael,

okay, I can reproduce the problem. I assume it is caused by the code which subtracts the inner area from the multipolygon area.
No idea if this can be fixed easily.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Forstner Michael <forstner-m at a1.net>
Gesendet: Dienstag, 26. September 2023 19:44
An: 'Development list for mkgmap'
Betreff: Re: [mkgmap-dev] Gaps in surfaces

Hello Gerd,

here is the area: https://www.openstreetmap.org/#map=19/48.57117/13.96920 I
understand that it is necessary to make rounding. If a point of two surfaces
is equal in OSM, the point should also be equal in Garmin.

Thank you!

Best regards,
Michael

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