[Tagging] [OSM-talk-be] cadastral plan now open data

André Pirard A.Pirard.Papou at gmail.com
Fri Sep 21 19:32:49 UTC 2018


Hi,

This is the e-mail I started writing 3 weeks ago and that was commented 
before being sent !

On 2018-08-24 13:58, joost schouppe wrote:
> Hi,
>
> The cadastral plan is now open data for the entire country!
Thanks a lot for the info Joost.
But there is a *BIG WARNING*.*
*PLEASE *DO NOT* use the WMS to trace, and I suppose that the import 
data exhibits the same problem.
I wanted wait to be sure that the 2018 shape data exhibits the same 
problems as the 2017 WMS but from the little i have seen (small 
definition) and what Lionel said it seems that pre-2018 errors remain 
unchanged.

For what I have seen of it in Wallonia, the Cadastre WMS map usually 
exhibits an error shift (wrong coordinates) as large as 10m and the 
houses and other elements have a wrong shape and location within the parcel.
See example below.
Instead, use JOSM with PICC in Wallonia and AGIV in Flanders.

The Cadastral map can be useful to:

  * find a house number not displayed on other maps
  * find a house not displayed on other maps, but do not rely on the
    house location (latlon)
  * trace boundaries, especially former municipalities', but be aware
    that Cadastre's boundaries are slightly different from other
    sources, in particular because they avoid crossing a parcel. They
    are official.
  * use names not displayed on other maps and in particular a very nice
    set of locality names
  * maybe use other features not needing a precise location

So, the usage of the cadastre is limited to displaying a JOSM layer, 
just for comparison with the PICC, aerial or other maps.
Even more than tracing, beware of importing cadastral data !
PLEASE DO NOT destroy with cadastre imports patient corrections with 
JOSM and PICC of ID and Potlatch inaccuracies and mistakes !!!

The following example uses some of the marvelous capabilities of JOSM to 
demonstrate a Belgian Cadastre shift of 7m.
Same text on this server 
<http://www.papou.byethost9.com/maps/Cadastre/JPD%20JOSM/>.

JOSM was opened showing OSM and, in an additional layer 1, the cadastral 
map of a friend's parcel.
I created a new JOSM layer 2 where I traced that parcel.
I created a second layer 3 where I traced from OSM my friend's house and 
garage to display them separately
*Picture 1* superimposes

 1. the thin cadastral map overlay 1 containing in pink a house alleged
    by the Cadastre
 2. in bold, the trace of the parcel B77k in overlay 2
 3. the gray shade house layer in layer 3

We can see that the pink house is totally phony in the cadastral map. It 
was probably destroyed long ago.


*
*
*Picture 2* superimposes the aerial map.
We can see that my friend's parcel extends a good 7m onto the road.
The whole cadastral map is offset by that 7m.
According to my friend, the most reliable limits of his estate are the 
ends of the SW wall
...



*Picture 3:* So, I dragged his parcel right onto the wall.
And now it's correctly located, aligned with the fencing all around.



*Picture 4:* This is the final, correct map.



*Picture 5:* and I used JOSM measuring tool.
The goal of these operations were for my friend to prove that a part of 
the sidewalk of the northern road belongs to him.
I made exports of these areas in GPX and OSM format.

The Belgian cadastre is not the only one with an error shift.
With JOSM, I have similarly proved that Google Map has a 120m NE shift 
in Beijing.
Nobody noticed it.




BTW, you can notice that the outline of the house is far from being the 
surface of the roof. It's 3m away from it.
That's because the outline represents the walls at ground level and the 
camera's axis and walls are slanted.
And you can notice too that the outline doesn't seem to match the ground 
at the baseline of the wall.
That's because of the height of the garage, that baseline it is not at 
ground level !!!
All in all, that picture shows extremely well how tricky the 
orthorectification can be to make the PICC map.
One cannot conceivably do that by hand.
Unfortunately, many contributors spend much time using ID and Potlatch 
to map house roofs.
Their work has to be redone with Areaselect, JOSM and PICC more 
difficultly than if it was done from scratch.

All the best,

André.


> That's pretty big because:
> - for Wallonia, it's the first open vector data with parcels, 
> buildings, roads and road names.
> - contains "underground buildings" which were not available anywhere 
> AFAIK.
> - there's a dataset with roads that have some kind of 
> "erfdienstbaarheid"/"servitude". This might be of use for certain 
> dubious paths
>
> But of course, please note:
> - there is way more data where this came from - the attributes of the 
> parcel are not included (like building levels, number of units, landuse)
> - Belgian cadastre data has a bad reputation in general so do not 
> trust everything you see. The building geometry seems to be quite 
> poor, especially when it comes to exact positioning, not so much the 
> shape itself.
> - do not trust road name data (it doesn't follow the CRAB name, so not 
> official in Flanders). Names are often abbreviated
> - the roads do not form a network, there are duplicate geometries and 
> some geometries are outdated by half a century
> - there is pretty good metadata included. However, you might find data 
> that does not follow the explained model
>
> The license file is included in any download. It seems to be 
> compatible with OSM, but it would be nice if more people give it a 
> good read. The first one to use it for mapping, does need to add it to 
> https://wiki.openstreetmap.org/wiki/Contributors
>
> The data is in shapefile format (boooo!), but Philippe Duchesne has 
> made a download site where you can get it in geopackage format. There 
> is also a "view" link. To actually see the data there, find the big 
> switches to activate the layers you want to see. The bigger ones take 
> a while to load!
>
> More details:
> * Official website:
> https://financien.belgium.be/nl/particulieren/woning/kadaster/kadastraal-plan
> https://finances.belgium.be/fr/particuliers/habitation/revenu_cadastral/plan-cadastral
>
> * Metadata:
> https://financien.belgium.be/sites/default/files/20180626_Dataspecificaties.pdf
> https://finances.belgium.be/sites/default/files/20180626_Specificationsdata.pdf
>
> * Repackaged into an open data format:
> http://data.highlatitud.es/cadaster-belgium/
>
> We think this data will only be usable for validation efforts. If you 
> think an import could be useful for some of the data in some places, 
> do not forget to follow the Import Guidelines or risk having your work 
> reverted.
>
> Happy mapping,
> -- 
> Joost Schouppe
> OpenStreetMap <http://www.openstreetmap.org/user/joost%20schouppe/> | 
> Twitter <https://twitter.com/joostjakob> | LinkedIn 
> <https://www.linkedin.com/pub/joost-schouppe/48/939/603> | Meetup 
> <http://www.meetup.com/OpenStreetMap-Belgium/members/97979802/>
>
>
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