[mkgmap-dev] tile takes very long time to generate

Sun Mar 14 11:44:33 GMT 2021

Hi all,

I've started a new branch called faster-mp, see http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=4609
and the corresponding download link on the bottom of http://www.mkgmap.org.uk/download/mkgmap.html

So far I've only started to remove "old-style MP" support. There are still some parts of the code that I don't fullly understand, so
I think I have to create a functional unit test next, containing all the special cases like incomplete data , MP which are only partly inside of a tile or covering a complete tile and maybe also incorrect MP which should still be rendered somehow.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Gerd Petermann <gpetermann_muenchen at hotmail.com>
Gesendet: Sonntag, 14. März 2021 09:47
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] tile takes very long time to generate

Hi Ticker,

the handling of the inner/outer role is indeed strange. The program calculates the "real" roles first, based on geometry. Later it checks if the given roles from the relation and may ignore the MP if no way has an empty role or role outer. This test should be done first or not at all.

I think it is a good idea to calculate the roles based on geometry, for empty roles we need the code for this calculation anyway. I just think that mkgmap shouldn't care too much about invalid geometries when data is complete.
I have to think again about those cases where data is not complete. Even with splitter and --keep-complete this can happen, e.g. when the input for splitter already contains incomplete relations.

Maybe mkgmap can simply ignore incomplete MP after logging a warning.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Samstag, 13. März 2021 12:21
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] tile takes very long time to generate

Hi Gerd

I think the extra testing should be removed and the logic should work
on the assumption of correct data; just emitting warning/errors when
problems are found during the normal processing.

It also has extra complexity due to early versions of the splitter not
keeping relations/polygons complete. Presumably this can be simplified
now.

role=inner/outer handling is strange, it looks like it totally ignores
it! Going with "assuming correct data", conflicting "inner" and "outer"
in a JoinedWay should be flagged, otherwise any "inner" or "outer"
should be believed, with all null being considered "outer".

Ticker

On Sat, 2021-03-13 at 08:32 +0000, Gerd Petermann wrote:
> Hi all,
>
> most of the time that is needed to process complex multipolygons (MP)
> is spent in compex tests which try to detect invalid geometries like
> "inner" ring is not inside outer or overlapping /crossing rings. I
> wonder if it really makes sense to perform those tests in mkgmap. In
> JOSM, the strategy is like this:
> The renderer is optimistic and assumes that the geometry is correct,
> for invalid geometries "garbage in -> garbage out" is used. The
> validator performs a lot more tests and should find all the special
> cases mkgmap is looking for. This test is slow but still much faster
> than that in mkgmap (maybe 30 secs in JOSM, many minutes in mkgmap).
> If mkgmap finds invalid geometries the behaviour is still rather
> unpredictable. I've used JOSM to create some test cases with "inner"
> overlapping "outer" and sometimes the inner is completely ignores,
> sometimes not. So, I really wonder what all the complex code is
> doing.
>
> I've attached my test file
> I am not sure if I should try to improve the test code
> 1) to be faster or
> 2) to be more predictable or
> 3) both 1+2 or
> 4) if I should just remove all code that isn't needed to produce good
> results with correct data
>
> Gerd

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