[mkgmap-dev] Splitting at country borders?

Sat Sep 19 17:18:21 BST 2009

On 19 Sep 2009, at 4:29 , Johann Gail wrote:

>
>> So is it possible to configure the splitter do split the maps not  
>> after
>> x-Number of nodes but at these coordinates?
>>
> No, this is not what I have written. There is some missunderstanding.
> The recent splitter is not able to split at geographical boundaries.
> This is the task of osmosis.

even osmosis can't do that. osmosis takes a polygon as input and  
doesn't read boundaries from osm files

> Maybe it is not too complicated to build this feature into splitter,  
> but
> at the moment it doesn't.

neither splitter or osmosis insert new points. but it is required to  
have boundary nodes in mkgmap. splitter would need to calculate  
crossing points with the boundary or a provided split polygon with all  
ways and insert the boundary points.

>> Or is it posilbe to do a presplit, which creates a tile for each  
>> country
>> and then in a second step splitting the country files?
>>
> Yes, this way should work. But for the presplitting you can't use
> splitter. I don't use osmosis by myself, so I don't know internals of
> it. But I know, that geofabrik splits its regions with osmosis.

you can do the presplit but routing can't work then across boundaries.
osmosis has different modes
- clip ways at the boundary -> no routing across tiles due to missing  
nodes
- include the whole way ->  long ways extend far beyond the boundary,  
areas aoutside the boundary will be incomplete, tiles will overlap in  
huge areas. routing may break in these overlap tiles
- don't clip the way but omit the points outside the box/polygon ->  
combining 2 osm files should work. but then why did you split them?

>> Then it would be possilbe to download europe from geofabrik, split it
>> into countries and then crate maps from it.
>> These maps would be interroutable. It would be also need less  
>> computing
>> power/memory for doing this compared of
>> processing the whole europe map
> I would expect the interstate routing to work. Precondition is  
> obviously
> that the presplitted tiles don't miss any segments at the border and  
> the
> border nodes have exactly the same coordinates.
>

still don't understand why this is useful. If you want multiple  
countries and route across countries and tiles why split it more than  
necessary and try to assemble again?

>
> Regards,
> Johann
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev