Jean-Marc Liotier wrote:
On 20/09/2012 13:18, Lester Caine wrote:
Go on wiping and reloading every time the source data is updated and manually
merging everything.
Sounds ugly doesn't it ? Because it is. Wouldn't it be much better if each
building from the cadastre had a UUID that could be traced so that differential
imports could be performed with little disturbance and little manual work ? Yes.
But sadly that is not how the French cadastre works : it is just a bunch of
georeferenced images.
So the user of cadastral data has to repair the buildings split where a
cadastral plot limit is drawn across, check for proper geographic referencing
using GPS traces, imagery and geodesic reference points, expunge the data that
describes buildings that are already in OSM, check the general sanity of the
data, remove the occasional artefacts... I don't like it either - it is a lousy
cadastre but that's the only one we have.
So would it not be better to provide it as an raster overlay instead? And trace
from that.
But I was assuming that this was vector data? So it can be processed into a
database? I am sure that from version to version they are not going to be
changing the coordinates of the majority of buildings? All that raw data can be
imported as a layer in OSM, but in addition it can be compared with a previous
import and identical elements ignored? That just leaves the changes between
versions to be processed, and you end up with a better version of the cadastre
data than the government ;) And reference it to the rest of the OSM data.
Some of us are playing similar 'tricks' with the UK OS data ...
--
Lester Caine - G8HFL
-----------------------------
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