[mkgmap-dev] Splitting at country borders?

Sun Sep 20 00:37:47 BST 2009

Apollinaris Schoell escribió:
> 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?
>   
If I understand right your question, I can give you a reason. I build 
maps for Spain, Portugal and South of France. If I could combine 
Geofabrik osm files so that routing would work, it would be much faster 
to download individual country files (~300 MB altogether), assemble them 
and split the resulting file with splitter than download all Europe (2 
GB->30 GB uncompressed) and processing such a big file to get my area of 
interest.
Regards
Carlos
>   
>> Regards,
>> Johann