[GRASS-user] Latitude/Longitude vs UTM

[Kurt Springs]

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.  They looked strange compared to what I generated before.  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.)  I then tried to run r.topidx.  This was interesting in that it told me that r.topidx could not be run with latitude and longitude and I had to convert to UTM.  I was wondering if this is the answer to the problem and I just had to convert to UTM.

One other question.  New Hampshire appears to fall within two UTM zones (19T and 20T)  Is there a way for a maps set to contain two UTM zones?

Thanks for any help.

Kurt Springs