Digital Chart of the World

[Nancy Greeley]

On Sept 25, "Nick" wrote the following message into the GRASShopper mail
list:

*******************************************************

>From: Nick Reddingius <nredding at BBN.COM>
Subject:  Re:  VPF conversion

Earlier this year we made an attempt as part of an Air Force project
to use DCW as a data source for GRASS.   The DCW access software is
rather intermixed with  the Borland interface code, which makes it
very difficult to just use the access software.  In fact, after we
played around with this for quite some time, we were told by ESRI,
the people who developed the software, that it would take THEM likely
several months to build a VPF-GRASS bridge.  A UNIX version should
be out by now, but I haven't seen it, nor have I heard whether it is
actually done.  For the time being, we've abandoned DCW as a source
of data.  Sometime in the future we may look into it again when the
product looks a bit more stable.   Also, be aware that the reading
of the cd-rom appears to be excruciatingly slow compared to other
cd-roms.  It isn't clear to me whether that is because of the way the
cd-rom is organized or because of something going on in the software.

*********************************************************

Sorry to say...Let us know if there is any, more positive feedback,
PLEASE!

-Nancy Greeley, USACOE, CRREL GIS Coordinator

 # an average for that entire area.
|>  
|>  Try using r.neighbors to average values over a number of cells (odd number
|>  required), and then cut the resolution down by the corresponding amount.
|>  
|>  e.g.
|>  Let's say you want to average in a 5x5 region for a map called "elev"
|>  
|>  g.region rast=elev
|>    Let's say this map is a 50m resolution 
|>  r.neighbors input=elev output=elev.avg method=average size=5
|>    You now have the averages you want, but the original rows and cols
|>  g.region res=250
|>    250 = 5 * 50 (50 is the original res and 5 is the size input above)
|>  r.mapcalc elev.avg=elev.avg
|>    elev.avg gets resampled every 5 rows and 5 cols (cutting memory by 25 times)
|
|Which value is the r.mapcalc picking when it is doing the resampling ?
|Is it doing it this way:
|
|X****X****X****X****
|********************
|********************
|********************
|********************
|X****X****X****X****   =>   XXXX
|********************        XXXX
|********************
|********************
|********************
|
|or this way
|
|********************
|********************
|**X****X****X****X**
|********************
|********************
|********************   =>   XXXX
|********************        XXXX
|**X****X****X****X**
|********************
|********************
|
|I think that r.mapcalc is doing it like in the first example and then the
|result of the average operation will be that the average output map is shifted two 
|pixels towards west and two pixels towards north.  
|Please correct me if I'm wrong !!!
|
|Lars
|
|Lars Schylberg                    Email: larss at fmi.kth.se  
|Department of Photogrammetry 
|Royal Institute of Technology     Tel.   +46 8 790 86 33   
|S-100 44  STOCKHOLM, SWEDEN       Fax.   +46 8 790 66 10
|
|
|
|
|
|


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Michael Shapiro                        U.S. Army CERL                  
email:   shapiro at zorro.cecer.army.mil  Environmental Division          
phone:   (217) 373-7277                P.O. Box 9005                   
fax:     (217) 373-7222                Champaign, Ill. 61826-9005
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