[OSM-dev] area filtering on change streams?

Peter Wendorff wendorff at uni-paderborn.de
Mon Jan 21 08:13:58 GMT 2013


Am 21.01.2013 08:00, schrieb Frederik Ramm:
> Hi,
>
> On 01/21/13 07:54, Brian Cavagnolo wrote:
>> I'm kinda hooked on the appeal of only working with the changeset.  I
>> poked around the osmosis source and learned a bit about the change
>> format.  It looks like changes could be filtered using the same code
>> used for the polygon and bounding box filters.  Does this sound
>> intuitively correct?
>
> No.
>
> The fact that changesets cannot be filtered by region is not a 
> software limitation, it is a design limitation.
>
> Changes can occur in nodes, ways, or relations; but only nodes have a 
> geometry given in the .osc file. For example, an .osc file might 
> contain the information "way #17 has been changed from 
> highway=residential to highway=unclassified" but you won't know if 
> that is relevant to you because the nodes of that way are not included 
> in the changeset (unless by chance they have been modified at the same 
> time).
While in fact you would know that (out of the fact, that the way already 
is in your database), the other way around it's a problem:
If a node changes it's location towards your area of interest, that has 
been outside before, every way connected to this node is of interest for 
you, but these ways are neither in your database (outside your area 
before) nor in the change stream (as the way object itself didn't change).
>
> If you really want to pursue this further, read up on "augmented 
> diffs" which are reference-complete and would therefore allow such 
> filtering: 
> http://wiki.openstreetmap.org/wiki/Overpass_API/Augmented_Diffs
>
> Bye
> Frederik
>




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