[mkgmap-dev] splitter: relations to be checked with keep-complete=true

Wed Dec 19 20:56:04 GMT 2012

Hi WanMil,

thanks for the detailed explanation. 
One small addition: splitter does also check if a way is closed. If that is
the case, it calculates
the bbox of the way and writes the complete way to all tiles that intersect
with its
bbox. If the way is not closed, it calculates the intersection based on the
line segments.
The same kind of calculation is done for multipolygons. A precise
implementation would use
java.awt.geom.area for these calculations, but I fear that will be very time
consuming and not much 
better.

Gerd

WanMil wrote
> I want to go a bit more into detail.
> 
> Splitter now puts the following things into a tile (Gerd, please correct 
> me if I am wrong ;-):
> 
> 1. All nodes that are within the tiles bounding box
> 2. All ways that intersect the bounding box including all nodes
>     (no matter if they are within the bbox)
> 3. All relations that contain a node or a way that is in the tile.
>    These relations need not be complete. Some nodes or ways can be
>    missing if they do not match the first two rules. Subrelations
>    are not handled.
>    Special rule:
>    Relations of the following type are always complete:
>    multipolygon
>    restriction
>    through_route
> 
> In more simple words these rules put all data into the tile that lies 
> directly in the tile or that might modify some data in the tile.
> 
> Obviously this will generate some questions.
> 
> - Why are subrelations not ignored?
> Subrelations are not handled by mkgmap so they can be ignored.
> 
> - Shouldn't route relations be complete in the tile?
> Route relations contain ways. It is possible with the relations style 
> file to modify ways and nodes based on the relation tags. But this makes 
> sense only with ways and nodes lying within or intersecting the tile 
> bounding box.
> 
> - Shouldn't boundary relations like multipolygons be complete in the tile?
> Yes, but...
> Adding all related boundary data to a tile increases the tile size very 
> much and makes sense only if the boundaries are used as polygons. At the 
> moment we don't know anybody who uses boundaries as polygons but lots of 
> users use them as lines to display the border names. All relevant data 
> for this is available in the tile (some relations are missing with the 
> current trunk version!).
> 
> - Why are the tiles sizes noticeably smaller compared to the trunk
> version?
> The main reason is that the trunk version puts complete relations to the 
> tile. If you have a motorway in the tile that is part of an e-road the 
> trunk version adds the whole e-road to the tile although you need only 
> the ways that intersect the bounding box.
> 
> 
> So my conclusion is: The patch fixes a (small) bug in the trunk version 
> (some missing boundary relations) and optimizes the tile size by putting 
> only data into the tile that theoretically can be used by mkgmap.
> 
> If someone wants to test that more in detail I propose to run splitter 
> with a small polygonfile, a small max-nodes number and xml output. Then 
> you can open the tiles with JOSM and see if everything you would expect 
> is contained in the tile.
> 
> WanMil
> 
>> Hi all,
>>
>> attached is version 4 of the patch, based on the problem-list branch.
>> WanMil and I found out that it reduces the size of splitter output files
>> (and run time) quite nice, but it also sometimes adds boundary relations
>> that were not output with r263, which in
>> turn changes the output of mkgmap a little bit.
>> We are not sure if this is acceptable for all, so please try this.
>>
>> Gerd
>>
>>
>>  > Date: Mon, 17 Dec 2012 06:41:40 -0800
>>  > From: 

> gpetermann_muenchen@

>>  > To: 

> mkgmap-dev at .org

>>  > Subject: Re: [mkgmap-dev] splitter: relations to be checked with
>> keep-complete=true
>>  >
>>  > GerdP wrote
>>  > > Attached is a patch for r263 that tries to implement WanMils
>> proposals.
>>  >
>>  > Stupid error: the patch did not filter type=route relations because
>> route is
>>  > contained in through_route.
>>  > Here is the corrected version.
>>  > limit_relation_types_v2.patch
>>  >
>> &lt;http://gis.19327.n5.nabble.com/file/n5740697/limit_relation_types_v2.patch&gt;
>>
>>  >
>>  > The amount of removed data is quite big, so it would be nice if that
>> still
>>  > is all that we need
>>  > for mkgmap.
>>  >
>>  > Ciao,
>>  > Gerd
>>  >
>>  >
>>  >
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