
Philip,

Thanks for the suggestion, but the problem isn't large flat areas.  It appears
that when there is a steep slope, every other "line" of pixels is showing a
slope of 0.  In the area that I'm working (West Point, NY) the relief is pretty
dramatic so I know this can't be correct.  I will try your suggestion of using
s.surf.tps anyway and let you know if it works.

Bill Green


> 
> Bill Green writes:
> > 
> > Second problem of the day:  when I use the r.slope.aspect command the results
> > appear very linear.  I am not the only one to experience this problem as 
> > someone who has worked with the data before generated the same linearized 
> > output.  Is this a function of the elevation map? If not how do I correct for
> > this problem?  Thanks again.
> > 
> Yes, it is probably due to your DEM, especially if the elevation 
> differences on your map are not extremely high. r.slope.aspect does
> a 3x3 neighbourhood filter known as Horn's method in order to determine 
> slope, and will therefore tend to come up with large flat area and 
> contour-like steep slopes in places where your pixel-value changes. 
> One possible solution is to re-interpolate your DEM (I don't know if 
> it comes from contourlines or elevation points) in cms or inches, in
> order to avoid large 'flat areas'. If you use s.surf.tps for this, 
> slope and aspect will be calculated at the same time, and probably 
> more accurately.
> 
> Hope this helps!
> 
> Philip Verhagen
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