[GRASSLIST:5497] Re: NVIZ and GTOPO30 on osx

[Glynn Clements]

Ian Macmillan wrote:

> > NVIZ doesn't like lat-lon locations; it acts as if the horizontal
> > units are metres. So, for a GTOPO30 DEM, you have a 40m x 50m region,
> > with 4000m high peaks (100 times the width of the region).
> > 
> > Importing into an X-Y or Plate Carée (Equidistant Cylindrical)
> > location should produce more sensible results.
> 
> Thanks for the tips, while these projections are a little better, they
> are still a little distorted. XY reads the file as 6000 rows by 4800
> columns, and consequently ~4000 units high, however a row is not 1
> meter across. Roughly the same problem with eqc.

If you are importing uncorrelated rasters, you have to specify the
correct bounds manually (using the north/south/east/west options for
r.in.bin, or by subsequently running r.support or r.region).

A GTOPO30 tile would be approximately 4500 x 5500 km, with a
resolution of ~ 1 km.

> Turns out the best
> thing is to bring in the gtopo30 from a lat-long location into a UTM
> location using r.proj. Then use nviz from the UTM location.

If you actually want a UTM projection, then you need to do this
anyway. However, if you don't care about the exact projection, using
eqc will allow you to use the raw GTOPO30 raster without any of the
error which projection will introduce.

-- 
Glynn Clements <glynn.clements at virgin.net>