[GRASS-user] EPSG code for KML

micha at arava.co.il micha at arava.co.il
Mon Jul 12 09:20:22 EDT 2010


> On Sat, Jul 10, 2010 at 6:33 PM, Hamish <hamish_b at yahoo.com> 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 '
>
>
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