[OSM-talk] French/Dutch caribbean island Saint Martin (Sint Maarten) not correctly positionned

[Pieren]

Hi,

I'm currently implementing the cadastre support in JOSM for the french
part of the island "Saint-Martin" shared with our Dutch friends (it is
a special projection).
The island is quite well mapped today, mostly from the hi-res Yahoo
imagery I guess:
http://www.openstreetmap.org/?lat=18.069&lon=-63.0746&zoom=13&layers=B000FTF

The problem is that the data, although they match the Yahoo imagery,
seem to be shifted from about 800 meters in north.
The French national geographic institut provides files about geodesic
reference points and one is marked on the main fortress here:
http://geodesie.ign.fr/fiche_geodesie_OM.asp?num_site=9712701&X=491000&Y=1998000
Here the details of one mark on the ground:
http://geodesie.ign.fr/fiche_point_OM.asp?num_site=9712701&no_ptg=01

So, the fortress should be at 18.0707416944 lat and -63.0851921944 lon
but in OSM it is at (approx.) 18.0705758642 lat and -63.0845414733 lon

My guess is that the Yahoo imagery is not correctly georeferenced. I
can fix this issue for the French part of the island using the
cadastre. But what about the Dutch part of the island ? It is probably
the same issue for the neighbourhood, e.g. Scrub Island, Dog Island
and Saint Barthelemy. Also how can we inform other mappers that the
Yahoo imagery is not correct in this area ?

Can someone from the Netherlands contact me and check with me what
could be done to fix this issue ?

Pieren