Re: WGS84 offset
Jason Cox <[email protected]>
| Newsgroups | gmane.games.flightgear.terragear.devel |
|---|---|
| Message-ID | <[email protected]> |
On Tue, 2004-06-01 at 20:54, David Megginson wrote: > Jason Cox wrote: > > > I need to create scenery for australia but have found that there is a > > problem in that all scenery is of by about 1km. Is there a way of > > setting an offset when the dem files are cut up and the layers are > > produced. > > Are you sure it's the DEM that's off? The 30 arcsec DEM can be up to 1km > off by definition (since that's its nominal resolution), but if you're using > the new 3 arcsec SRTM data, it should all be in the right place, aside from > the occasional anomaly I am using self produced 3 second dems. These are produced from Mapinfo mif files. > What is it that the elevations do not sync up with? Is it the airports, > shoreline data, or land use data (i.e. cities, roads, rivers, forests, > etc.)? Airports should be pretty accurate, though there are still some > problems. The GSHHS shoreline data for inland bodies of water is pretty > bad: it is more than 1km off in the Great Lakes for Canada and the U.S. (so > waterfront airports are either floating out in the lake or far inland), but > the other hand, vmap0, while less detailed, is pretty-much bang-on. > However, Norm has pointed out that vmap0 can be way off on the *ocean* > coastline data, while GSHHS is usually accurate. I am finding that the all layers are out in Australia. I have seen that there is a program in terragear called "wgs83offset" under the Prep source tree ., But what do I do with the offset info once obtained > One thing worth noting is that vmap0 data we use for land use is based on > 1:1,000,000 World Aeronautical Charts (WAC) and similar publications. On a > printed WAC, a 1 km error is barely noticeable because of the low resolution > (nominally 1mm=1km), so it shouldn't be surprising to find errors like > those, especially outside of North America where the data have not been > tested as much. There are much better-quality free data available for the > U.S., but the rest of the world, unfortunately, hoards its geographical data > so that we cannot use it. The Site I get my local data from is http://www.gs.gov.au , they have it in arcInfo amd MapInfo format at 1:1,000,000 from memory > > All the best, > > > David > > _______________________________________________ > Terragear-devel mailing list > [email protected] > http://mail.flightgear.org/mailman/listinfo/terragear-devel --