[GRASS-user] Looking for technique to equalize shading of adjacent Aster dem tiles

[Michael Barton]

There are 3 ways to do this in GRASS.

1. Patch all the tiles together (r.patch) and then add a grey color table to the patched image (r.color). This will probably give the best results.

2. Pick one tile that has the widest range of elevation values and give it a grey scale color table. Then copy the color table from that tile to all the rest with r.color.

3. (A varient of #2). Create a custom color table ranging from black (for the lowest elevation) to white (for the highest elevation) for the total elevation range of all the tiles. Create this for one tile and then copy it to all the other tiles. You can create a custom color table in a text file or from the "color rules" menu selection. To create a color rules text file, assuming that 100m is the lowest elevation of all tiles and 3000m is the highest elevation of all tiles, you simply put the following into a text file, save it, and then add it to every tiles using r.color.

====  text file contents ====
100   black
3000 white
======================

Michael


On Jun 4, 2012, at 1:00 PM, <grass-user-request at lists.osgeo.org>
 wrote:

> From: Helmut Kudrnovsky <hellik at web.de>
> Subject: Re: [GRASS-user] Looking for technique to equalize shading of adjacent Aster dem tiles
> Date: June 4, 2012 2:36:44 AM MDT
> To: <grass-user at lists.osgeo.org>
> 
> 
>> One of my aims is to take a nice grayscale image to use in deforming mesh
> topology.  The circuit straddles >two tiles and the shading is markedly
> different.
>> 
>> How can I either fix one or re-color both from scratch based on the
> elevation data?
> 
> maybe build a virtual gdal data set [1] [2] of the Aster dem tiles, link [3]
> or import [4] them and use these tiles as one dem dataset for shading?
> 
> [1] http://www.gdal.org/gdalbuildvrt.html
> [2] http://www.gdal.org/gdal_vrttut.html
> [3] http://grass.osgeo.org/grass64/manuals/html64_user/r.external.html
> [4] http://grass.osgeo.org/grass64/manuals/html64_user/r.in.gdal.html
> 
> -----
> best regards
> Helmut
> --
> View this message in context: http://osgeo-org.1560.n6.nabble.com/Looking-for-technique-to-equalize-shading-of-adjacent-Aster-dem-tiles-tp4978868p4978907.html
> Sent from the Grass - Users mailing list archive at Nabble.com.
> 

_____________________
C. Michael Barton
Visiting Scientist, Integrated Science Program
National Center for Atmospheric Research &
University Consortium for Atmospheric Research
303-497-2889 (voice)

Director, Center for Social Dynamics & Complexity 
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu





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