<br><br><div class="gmail_quote">On Sat, Jul 10, 2010 at 6:33 PM, Hamish <span dir="ltr"><<a href="mailto:hamish_b@yahoo.com">hamish_b@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">Bulent wrote:<br>
> I occasionally use Google Earth –GE– (kml files) and I am aware of the<br>
> fact that there is a bit of distortion (i.e., metric offset) between GE<br>
> and other projections for a variety of reasons. I am wondering if anyone<br>
> knows whether there is an EPSG code for KML format so that I can create<br>
> a LOCATION in Grass using this code and avoid/minimize such distortions<br>
> when I import vector files. <br>
<br>
</div>It is fundamentally broken, do not use it for serious GIS work. It is<br>
only valid for visual use and saving cpu cycles on large deployments.<br>
(which is both acceptable and very important for folks like google)<br>
<br>
(epsg initially refused to include it but finally caved to mass user<br>
pressure)<br>
<br>
but if you do want to use it, it's just the mercator projection with<br>
a spherical ellipsoid using the WGS84's ellipsoid's major Earth radius<br>
as the only sphere radius. quite simple to define.<br>
<font color="#888888"><br>
<br>
Hamish<br>
-----------<br></font></blockquote><div><br></div><div>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. </div>
<div><br></div><div>' 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 ' </div>
</div><br clear="all"><br>-- <br>BÜLENT<br>