[GRASS-user] Re: [GRASSLIST:1173] Downscaling DEMs (need some feedback)

[Michael Barton]

It actually can come out quite nice, but I agree with Wolfgang that you
should try it on a small area to experiment first.

r.resample.rst will reinterpolate down (or up) and not (in theory) produce
those annoying 30 ghosts.

If I remember, you need to start out at the extents and resolution of the
original 30m map, however.

You can also start with your original map, create a bunch of vector points
(xyz) (up to several per original grid square) and then reinterpolate using
v.surf.rst.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics and Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton


> From: Wolfgang <wollez at gmx.net>
> Date: Mon, 07 Aug 2006 22:59:30 +0200
> To: <grassuser at grass.itc.it>
> Subject: [GRASS-user] Re: [GRASSLIST:1173] Downscaling DEMs (need some
> feedback)
> 
> Downscaling is quite difficult, much depends on our area you are in. I
> was resmpling some SRTM data to 15 meter resolution and it was not that
> easy.
> 
> But have a look at r.bilinear or r.resamp.rst all parameters depend
> quite much on your topology and sometimes I found it it quite helpful
> not to do it in one step ( at least for r.resamp.rst). But I'm
> absolutely not a guru in this field. Just try it out on a small region.
> 
> Cheers
> Wolfgang
> 
> Jonathan Greenberg schrieb:
>> I'd like to resample a 30m DEM to 4m for use in the ATCOR3 topographic
>> correction software package.  The issue that always pops up when doing
>> downscaling like this is that the resultant "higher res" DEM contains the
>> "ghosts" of the 30m pixels (e.g. it creates squares in the landscape).  My
>> question is, what (if any) are the best ways to "get rid" of these effects?
>> Does GRASS (or other packages) have any tools to deal with this?  It seems
>> that the major issue is that a basic raster resampler treats the DEM as a
>> flat surface of equal elevation, but treating it as a grid of points, where
>> the center of each cell = the elevation, would be more appropriate (and
>> then, for each cell that is not the centroid of a DEM cell, the value is
>> some distance weighted function of the 4 elevation values which will
>> surround it).  Thoughts?
>> 
>> --j
>> 
>> --
>> 
>> Jonathan A. Greenberg, PhD
>> NASA Postdoctoral Researcher
>> NASA Ames Research Center
>> MS 242-4
>> Moffett Field, CA 94035-1000
>> Phone: 415-794-5043
>> AIM: jgrn3007
>> MSN: jgrn3007 at hotmail.com
>> 
>> 
>> 
> 
>