OpenStreetmap HADW wrote:
A couple of days ago, I walked a footpath, which turned out, along with the preceding private road, to be a PROW on foot. As I wanted to detail map it to show steps, I first calibrated Bing against OS StreetView
When using any OS data it's important to be certain of the method used for the datum conversion. If it's not using the OSTN02 table-driven conversion you should expect to see offsets. The OS documentation says that the less-accurate method is OK for up to +/- 5m, but my experience is that the offset can be greater than that, e.g. up to about 20m. If you ever see offsets of this magnitude in anything that has touched OS grid references or OSGB36 datum, be suspicious! (As an example, http://hills-database.co.uk/ *deliberately* uses the less-accurate conversion because they claim that GPS devices will typically use the less-accurate conversion back to WGS84 when you enter a grid reference. As a consequence, if you display their summit positions on a not-reprojected OS map, they will be in the wrong places.) Cheers, Phil. _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-gb
