Fwd: Re: [GRASS-dev] VTK export for lat-long locations

[Soeren Gebbert]

Am Dienstag, 6. März 2007 23:48 schrieb Hamish:
> Sören Gebbert wrote:
> > I dont think this is a good idea. It is a nice and easy approach
> > indeed, but IMHO the length of the z height does not depend on
> > the length of a line on the surface.
> > So the z elevation is independend from the positon
> > on the surface (i know the earth is not a perfect sphere ... ;) ),
> > in this case the row number.
>
> the units of z are map dependent and not knowable by the system.
>
> for NVIZ + lat/lon, in the past I have used r.mapcalc to make a new
> map, [I've got a feeling this is no longer needed??]
>
> e.g. for a lat/lon map with z in meters:
>
> r.mapcalc "scaled_map = (map / 1850.0*60)"
>
> so x,y,z are all in degrees.

In this case
r.out.vtk input=ll_map output=ll_map.vtk elevscale=0.000009009
will do the job. :)

>
>
> I would not bother with reprojecting lat/lon into square cells, the user
> can to that with r.proj if they want. Just note that the output is in
> Plate Carrée like GRASS renders for 2D.

Ok, thanks.

Soeren

>
> see also 'r.shaded.relief units='.
>
>
> Hamish
>
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