[GRASS-user] Latitude/Longitude vs UTM

[Markus Metz]

On Fri, May 14, 2010 at 5:05 AM, Kurt Springs <ferret_bard at mac.com> wrote:
> Hi Folks,
>
> I have been playing with the seamless maps from the USGS.  Specifically, my question is on the effect of Latitude/Longitude vs UTM with respect to hydrology modules such as r.watershed and r.topidx.  I was trying to generate watershed maps with r.watershed.  I've done this before for my dissertation.  They did not turn out the same.

Are the region settings the same? Is the resolution of the new DEM
identical to the old DEM? Resolution and extend must be identical if
you want to compare results.

> They looked strange compared to what I generated before.

In what way?

>  Moreover, they maps kept falling in the same place in the map set regardless of what I turned off or on.  (i.e.  some where in the center top, when the map was generated from a dem on the bottom.)

Was the computational region set to the resolution and extends of the
dem on the bottom?

The current computational region influences heavily the results of any
raster map processing. If current extend and resolution are not
properly set, the results may be astonishing.

Markus M