Jon, Thanks for the links, however I was only able to get the first one to work. [The second link gave me a blank page with a horizontal slider bar at the top.]
I also would like to thank Chris for let me know the source of the spatialreference map data, vmap0. I found the vmap0 data on the Nima web site. I downloaded a copy and compared it with our old map database. It was almost a perfect match except for a few tweaks (assuming some adjustment/corrections have been made over the last 10 years). It seems this is where our original data came from. After spending some time looking at OSM, vmap0, and satellite images, I'm finding that the vmap0 data has problems. In a very telling instance, I found a chain of islands northeast of Cuba. Some vmap0 islands are to the right of the OSM islands, and some are to the left. In all cases, the OSM islands overlaid those from the satellite photos. So I believe the discrepancies I'm seeing in the location of Alderney Island is really due to errors in Nima's vmap0 data. Brad -----Original Message----- From: Jon Burgess [mailto:[email protected]] Sent: Wednesday, September 15, 2010 11:51 AM To: Simpson Brad-C-Lockheed Cc: Christopher Schmidt; Dane Springmeyer; mapnik-users; Robert Coup; [email protected] Subject: RE: [Mapnik-users] Projection problems On Wed, 2010-09-15 at 09:34 -0600, Simpson Brad-C-Lockheed wrote: > Chris, > > Thanks for responding. I understand the spatialreference map is coarse and > low resolution. However, my position is all coordinates in the general area > are shifted (although I have only looked in the English Channel area and the > Greek Islands so far). And the vmap0 data matches our database. I've only > given one example that is easy to confirm. I do not believe this is a case > of the data being too coarse. > > I would like to migrate from our old database (heritage unknown) to > openstreetmap, but I can't unless I can account for this discrepancy. This map comparison between OSM and Google satellite shows a good match: http://tools.geofabrik.de/mc/?mt0=mapnik&mt1=googlesat&lon=-2.22122&lat=49.701&zoom=16 This comparison with Yahoo satellite data also shows a good match: http://sautter.com/map/?zoom=13&lat=49.70034&lon=-2.22001&layers=00000BTFFFFFFF It looks like the footpath shown in OSM has been uploaded as a GPX trace which seems to add further confirmation that the island is probably shown in the correct position in OSM. I guess you can look for more 3rd party data to confirm the location, or failing that, you'll need to go there yourself :) Jon _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
