[GRASSLIST:1168] Re: (no subject)

[Markus Neteler]

Hi Andrzej,

On Tue, Nov 21, 2000 at 10:35:45AM +0100, Andrzej Wroblewski wrote:
> Dear grass users
> 
> I have couple problems:
> 
> 1. It's obvious that picture made from satelite in mountain terrain have different illumination of slopes.
> That cause different pixel values on satellite image. 
> Is in grass any function elimination that problem?
More or less :-) I have written a module for atmospheric correction and
terrain correction of satellite images:
http://www.geog.uni-hannover.de/users/neteler/index.html#sma
-> Presentation at Irst/Trento, Italy 

I wanted to release these modules already, but don't have much time.
Perhaps I can send a version to you. Please contact me personally.

> 2. Haw to streach contrast in grass?
Try i.grey.scale or r.colors 
 
> 3. r.mapcalc
>      >out=(ch3/ch1)*90
> when complete writes:
> min values 0, max values0
> (ch1 and ch3 are my landsat band 1 and 3)
> why? what's wrong?
If you are using GRASS 5, floating point numbers are stored *only*
if the right side of the equation has floating points (90.0 instead of
90). Your line should be

 out=(ch3/ch1)*90.
or
 out=(ch3/ch1)*90.0

Please try this.

Kind regards

 Markus Neteler