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. ' 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 ' -- BÜLENT
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