[OSM-talk] Fetch whole relation when parts of it are in bbox

Steve Coast steve at asklater.com
Wed Nov 7 08:33:39 GMT 2007


On 3 Nov 2007, at 14:33, Robert (Jamie) Munro wrote:

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> Jannis Achstetter wrote:
>> Hello there,
>>
>> I've got a problem with one specific tile:
>> http://www.informationfreeway.org/?lat=49.974240779456515&lon=9.44955088920595&zoom=12&layers=0B00F000
>>
>> You see that "inverted" tile right in the middle? This is actually  
>> not a
>> bug in osmarender but in the API as far as I can see. I looked at the
>> .osm-file it gets from the server and if I were the renderer I would
>> have drawn it pretty the same as you can see this now. The problem  
>> is:
>> We do have a multipolygon-relation here with the outer area (more  
>> than
>> 1000 nodes) and some smaller areas which are no forests. Now I ask  
>> the
>> API to give me the area and it does only return the smaller sub- 
>> areas,
>> not the outer one (meaning: only a part of the relation). So, how  
>> do I
>> know that these are no forests?
>> Wouldn't it be good if the server would give me the whole relation  
>> and
>> not only the parts that are inside the bbox? Would this introduce any
>> problems for osmarender or other software?
>> Technically I think this will not be a too huge problem since the  
>> server
>> returns a whole way when only a part of it is inside the requested  
>> bbox,
>> so why can't we do the same with relations?
>
> Because relations can be big. You don't want to download the whole M1
> motorway from London to Leeds just because you are working near Brent
> Cross shopping centre. Also, do you then download all the relations of
> all of the ways that you have downloaded?

That was the argument for not including all segments that were part of  
a way which crosses a bounding box (that stopped in 0.4)

> (personally, I think that returning all the nodes of a way even when
> they are outside the bounding box is a bad idea unless you have  
> actually
> asked for them).

ah..

have fun,

SteveC | steve at asklater.com | http://www.asklater.com/steve/






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