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[mkgmap-dev] r3678 and overview map problems

From Gerd Petermann GPetermann_muenchen at hotmail.com on Sat Jul 9 07:14:16 BST 2016

Hi Thomas,

okay, I have now checked your test case as well.

I think Steve has already explained why the change in r3674 introduced the problem,

the newer versions read the input files in sorted order when creating the overview map,

older releases used the order given in the command line.

A simple work-around would be to use higher numbers for the tiles which should be processed later,

e.g. 9999 instead of 4000 for the contour tiles.

A better solution would be to detect the needed resolution. The problem here:

mkgmap has to read all input tiles (completely) to find out which one uses the lowest resolution,

current code doesn't allow to read only the levels info. So one has to accept a longer run time.

I don't know if that is really needed, maybe an empty overview map can always use a low resoltion

like 12?

Another solution would be to evaluate the overview-levels option as suggested by Steve.

In your case the overview map is empty, it contains only the 0x4a polygons, so it is quite simple.

I have no idea what mkgmap should do when a user tries to combine ovm*.img files which were

created with different overview-level options, I leave that open.

I've impemented both alternatives in the attached patch, a binary based on r3678 is here:


The patch solves your problem, but I'd prefer to avoid the additional reading of all input files

before the overview map is produced.

@all : What do you think about the alternative to use a fixed resolution of 12 for an overview map

that contains only the tile boundary infos?


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Thomas Morgenstern <webmaster at img2ms.de>
Gesendet: Freitag, 8. Juli 2016 20:41:08
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] r3678 and overview map problems

Hi Gerd , Update:

r-3778 create now 1 0x4a like expected. This is a good news. But in my testenvironment are 2 osm-tiles and 1 contourtile. One of the osmtile has a wrong position. it is shifted to east ~22 degrees. The tile itself has 25.4 degreees east-west .

Am 08.07.2016 um 16:49 schrieb Thomas Morgenstern:
Hi Gerd,
i have tested r-3677 and the preview in my case is  wrong.
I think the error is not due to the TileSize. The error occurs, if the 2 OSM- tiles be used and 1 or more Contourline tiles in addition. The transparent contourlinetiles lie within the OSM tiles (1 degree square grid). If only used the OSM-Tiles, then the preview is okay and has the expected size with one Mapselectionarea. You can download my test-environment from http\img2ms.de\Downloads\Test.rar. Inside the rar are 3 tiles  and my mkgmap -bat.


Am 08.07.2016 um 09:54 schrieb Gerd Petermann:

Hi all,

I got no feedback on the do_not_split_0x4a_polygon.patch which I provided to fix the problems reported by

Thomas and Andrzej, see


I checked older versions of the source and

found out that older versions of the code did contain a special treatment for the 0x4a polygons, I removed those

in the overview2 branch and I don't exactly remember why, so I've reverted that part of the change.

I have the feeling that the code should be changed somewere else, the tests in PolygonSubdivSizeSplitterFilter.java

were introduced by WanMil long before we changed the split algo in MapSplitter.

Both sources use diverse hard coded limits, and I have no idea why these are not relevant for 0x4a polygons.

I assume that there is a maximum tile size (at least we have it in splitter) so maybe mkgmap should stop with an error

message when one tries to create a map with larger tiles?


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