[GRASS-user] Re: EPSG code for KML (micha@arava.co.il)

[Michael Barton]

FWIW, I've been teaching a workshop on basic GPS + GIS for archaeology in China, using QGIS. 

For the Mac at least, the QGIS GPS tools don't work--or don't work correctly. I've got the latest and greatest GPSBabel and QGIS 1.4. The QGIS GPS plugin cannot find GPSBabel. It seems this is because it is assuming that it is set up like on Linux instead of like on the Mac.

Michael
____________________
C. Michael Barton
Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University

Date: Mon, 12 Jul 2010 16:20:22 +0300
From: micha at arava.co.il
Subject: Re: [GRASS-user] EPSG code for KML
To: "Bulent Arikan" <bulent.arikan at gmail.com>
Cc: grass-user at lists.osgeo.org
Message-ID:
        <39b431e3aa73dab567afde4e1465855e.squirrel at webmail.arava.co.il>
Content-Type: text/plain;charset=windows-1255

> 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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