[OSM-talk] Import guidelines proposal update

Lester Caine lester at lsces.co.uk
Thu Sep 20 14:13:20 BST 2012


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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