On Apr 10, 2009, at 11:22 PM, <[email protected]>
wrote:
From: Markus Neteler <[email protected]>
Date: April 10, 2009 11:12:40 PM GMT-07:00
To: Tripp Lowe <[email protected]>
Cc: GRASS user list <[email protected]>
Subject: Re: [GRASS-user] NED Shaded Relief, Grass 6.4
Tripp,
On Sat, Apr 11, 2009 at 8:05 AM, Tripp Lowe <[email protected]>
wrote:
Hello Folks,
I am trying to create a shaded relief map based on a 30-meter NED
file using
r.shaded.relief. The results are very 'blocky' (or stair-
stepped). Running
a 5-cell average neighborhood across the DEM did not help. Can
somebody tell
me the correct procedures I should follow to create the relief map
that is
smooth?
I've put a screenshot of my initial shaded relief map up here to
show you
what I'm talking about...
http://www.rlogis.com/GMaps/test/grass64_shadrel.jpg
did you run
g.region rast=your_ned_map -p
before
r.shaded.relief
? I suspect that your current region is of lower resolution right now.
Markus
Additionally, NED data are not very good in this respect. In many
(all?) cases, they are DEM's interpolated from contour maps, which
were hand or machine drawn from aerial photo data with surveyed
reference points. They tend to have inherent stair steps. So even if
you get rid of the blocks, it still probably won't be the kind of
shaded relief that you want. For North America, the 30m SRTM level 3
or 4 data are much better.
Michael
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