[OSM-talk] All you've ever wanted to know about the french cadastre

[THEVENON Julien]

>>>> De : Lester Caine <lester at lsces.co.uk>

>>>> Now that I understand what is going on, I can see where some off the 
'extra' lines come from, and the diagonal is probably due to a boundary 
detail from changing sheets.

This is more often due to split of landuse ownership. There is no differences between this lines and the one separating adajacent buildings


>>>> However while the source has two different 
shades of block for buildings.
>>>>I don't think they can be used at this 
stage to provide useful extra lines.
>>>>The process that is extracting the 
vectors should further process the data so that each block IS a single 
continuous outline?
>>>>Later comparison will then be easier as long as say 
90% of the area matches the previous instance?


No this is not sufficiant I think because some times you have adjacent buildings that are not a single building. You also have cases when line separate building parts which have different number of levels or which are "light buildings" ( without wall by example )


>>>> Of cause simply 
importing thousands of these objects without a visual check of every one of them is something completely different to hand tracing every one of 
them.
>>>> I'd prefer that there was some cross check that objects have been 
verified.
>>>> And in my book, having to manually select objects to import 
would provide that check?
>>>> So I'd block any area select function, so that hundreds of objects can't simply be picked and pushed?

Please also notice that this is sometime not easy to distinguish on aerial imagery if the split line really exist or not.

Cheers
Julien
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