> On Sat, Jul 10, 2010 at 6:33 PM, Hamish <[email protected]> wrote: > >> Bulent wrote: >> > I occasionally use Google Earth –GE– (kml files) and I am aware of the >> > fact that there is a bit of distortion (i.e., metric offset) between >> GE >> > and other projections for a variety of reasons. I am wondering if >> anyone >> > knows whether there is an EPSG code for KML format so that I can >> create >> > a LOCATION in Grass using this code and avoid/minimize such >> distortions >> > when I import vector files. >> >> It is fundamentally broken, do not use it for serious GIS work. It is >> only valid for visual use and saving cpu cycles on large deployments. >> (which is both acceptable and very important for folks like google) >> >> (epsg initially refused to include it but finally caved to mass user >> pressure) >> >> but if you do want to use it, it's just the mercator projection with >> a spherical ellipsoid using the WGS84's ellipsoid's major Earth radius >> as the only sphere radius. quite simple to define. >> >> >> Hamish >> ----------- >> > > I was wondering about this. I read several online articles about the > problems and the doubts that EPSG has. Unfortunately, I was planning to > use > this for my archaeological work, which requires accuracy such as locating > the trenches and the features, like walls. My issue is, when I need to > show > polygons (e.g., a rectangle representing a trench), I transfer my GPS > points > (the readings at 4 corners) to GE and create a polygon there, save it as > KML. Then, I open this in QGIS, make a shape file there and import it into > GRASS. I suspect there is some distortion and this is a far too > complicated > routine but I do not know a more practical way.
I'm curious: Did you try the GPS Tools plugin in QGIS? You can simply import the waypoints. They will be in Lon/Lat WGS84, avoiding any of the problems with GE projections. THen, in QGIS make your polygons, and when you save as shapefile, choose any CRS you want for re-projection. Thus your original GPS points, and the polygons will always be in Lon/Lat geographic CRS. And for mapping/measuring you can choose any appropriate CRS. > > ' v.in.gpsbabel ' works fine for retrieving points and tracks from my > device. Alternatively, I may digitize the points to create polygons after > they are imported in GRASS. I still have to try ' v.in.ascii ' > > > -- > B�ENT > > This mail was received via Mail-SeCure System. > > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > > This mail was received via Mail-SeCure System. > > > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
