[GRASS-user] Re: i.atcorr negative DEM

[Elena Mezzini]

Elena Mezzini wrote:
> 
> 
> Markus Metz-2 wrote:
>> 
>> On Tue, May 17, 2011 at 10:08 PM, Elena Mezzini
>> <elena.mezzini at gmail.com> wrote:
>>>
>>> On Tue, May 17, 2011 at 9:22 PM, Elena Mezzini
>>> <elena.mezzini at gmail.com> wrote:
>>>> Hi all,
>>>> I'm once again in trouble with i.atcorr in GRASS6.5.svn.
>>>> I notice that my output reflectance images are strange: there are some
>>>> areas
>>>> that are really bright and other that are really dark. Both seem to
>>>> match
>>>> with my DEM raster.
>>>> Could there be problems with negative values in DEM?? I'm in a coastal
>>>> area
>>>> and there are some real altitude negative values.
>>>
>>> i.atcorr (the 6S code it is using to be exact) should treat negative
>>> elevation values as elevation = 0. It is debatable if this is correct,
>>> but in theory i.atcorr should behave accordingly. Actually, I am not
>>> sure about it's behaviour for negative elevation values...
>>>
>>> You could set all negative elevation values to zero,
>>>
>>>
>>> Ok, how can I do it?
>>>
>> replace my_elevation with the name of your elevation map:
>> 
>> g.region rast=my_elevation
>> r.mapcalc "elevation_positive = if(my_elevation < 0, 0, <my_elevation>)"
>> 
>> 
>> 
>> g.region rast=dem_sross_srtm
>> r.mapcalc "dem_sross_srtm_pos = if(dem_sross_srtm < 0, 0,
>> <dem_sross_srtm>)"
>> 
>> Syntax error!
>> As you know I'm not a programmer... where is the error?
>> 
>> Thank you once again
>> 
>> Elena
>> 
> 
> Found:
> 
> g.region rast=dem_sross_srtm
> r.mapcalc "dem_sross_srtm_pos = if(dem_sross_srtm < 0, 0, dem_sross_srtm)"
> 
> Sorry!
> 
> Elena
> 

No differences between negative and positive values...
I don't know what could be the problem...

Thank you for your helpfulness!

Elena

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