[GRASS-user] Re: Is it possible to export a Raster to KML

Jamie Adams jaadfoo at gmail.com
Fri Oct 28 18:08:14 EDT 2011

Roger is correct.  GE will just drape your raster data over it's terrain
mesh regardless of what vertical parameters your data has.  It is
essentially 2D with a z value and is interpreted as such.  That is why
EPSG:4326 works, because GE doesn't care about any other information.  No
conversions/shifts occur.

I export rasters from GRASS, generate hillshades, and overlay in GE using
gdal2tiles daily.  I seldom see any alignment issues, and when I do it is
usually my data.  Of course there are alignment issues in GE, but they will
vary place to place regardless of topography.

- Jamie

On Fri, Oct 28, 2011 at 2:06 PM, Roger André <randre at gmail.com> wrote:

> I find this thread interesting.  In my experience overlaying both raster
> (orthophoto) and vector data in Google Earth with KML, EPSG:4326 has worked
> with no problems whatsoever.  So far as I know, GE does not apply a vertical
> datum, it simply drapes the 2D data over its internal terrain model.
> Would it be possible for you to share some data where you have seen that
> this is a problem?
> Thanks,
> Roger
> On Fri, Oct 28, 2011 at 1:05 PM, Hamish <hamish_b at yahoo.com> wrote:
>> Helmut wrote:
>> > ...
>> > > in my experience overlaying kml (vector and raster)
>> > > with EPSG:4326 in google
>> > > earth works relatively well in flat areas, in mountain
>> > > areas there are
>> > > sometime distortions therefore.
>> Markus:
>> > I can confirm this from my (limited) experience to export
>> > data to KML. To correct for the geoid heights, you could use
>> > the previously indicated map and calculate the local
>> > ellipsoid-geoid difference and vertically shift your vector
>> > data with v.transform.
>> > Then export to KML. For raster, use r.mapcalc to shift.
>> n.b., IIUC raster KML support in google earth is essentially a
>> hack building on/abusing their raster-icon support.
>> they may have improved things, but this is what I was lead to
>> believe at the time of writing r.out.kml.
>> probably it is useful to consider if the ellipsoid-geoid
>> difference is important vs. the overall vertical differences
>> in the data, if the result is just for viewing maybe it is not
>> worth the trouble.
>> Hamish
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