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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