[GRASS-user] Problems creating new map with r.mapcalc

[Lars Forseth]

Hi!
I wonder if anyone could explain to me how to create a new map (raster) from 
two pre-existing maps, in mapcalc. Because I have problems with understanding 
how to do this in r.mapcalc

I have two raster datasets that I would like to combine like so; if the cell 
is in map a, assign the value 7; if it is in map B, assign the correct value 
from B, (i.e keep the value the cell already have in B).

I have tried to read "Performing Map Calculations on GRASS Data: r.mapcalc 
Program Tutorial", by Marji Larson, Michael Shapiro and Scott Tweddale, U.S. 
Army Construction Engineering Research Laboratory (December 1991) , and they 
give this example:

MAPCALC> aspect.str = if(streams,26,aspect)

This should then give a new map that contains the values from "aspect", but 
with the value 26 assigned to cells with "streams".

Example from my experiments:
R_test9 = if(R_VannA at larsf == 1,7, R_paramNew at larsf )

This makes a new map; but it contains only 7, were there was data in R_vannA, 
and else, NULL (I guess), see otput below of r.info.

I also tried "R_test9 = if(if(R_VannA at larsf == 1),7, R_paramNew at larsf ) ; and 
this gives the same (non) result. And "R_test10 = if(R_VannA at larsf, 7, 
R_paramNew at larsf)"; also the same as; I.E not what I wanted. The problem is 
that it never assigns a value from R_paramNew at larsf!!!

What am I missing? Or doing wrong?

Regards
Larsf


Running; SUSE 10.3, grass63 dated 12.09 from 
http://download.opensuse.org/repositories/Application:/Geo/openSUSE_10.3/i586/


---------------------------------------------r.info output (example)
> (3) r.info map=R_test9 at larsf
> 
> +--------------------------------------------------------------------------
>--+
>
>  | Layer:    R_test9 at larsf                  Date: Sun Sep 21 15:28:36 2008 
>  |   | Mapset:   larsf                          Login of Creator: larsf    
>  |       | Location: Frosta                                                
>  |           | DataBase: /home/larsf/grassgis                              
>  |               | Title:     ( R_test9 )                                  
>  |                   | Timestamp: none                                     
>  |                       |
>  | ------------------------------------------------------------------------
>  |----|
>  |
>  |   Type of Map:  raster               Number of Categories: 7            
>  |   | Data Type:    CELL                                                  
>  |     | Rows:         3360                                                
>  |       | Columns:      3720                                              
>  |         | Total Cells:  12499200                                        
>  |           | Projection: UTM (zone 32)                                   
>  |        | N:    7062800    S:    7046000   Res:     5                    
>  | | E:     596600    W:     578000   Res:     5                     |
>  | Range of data:    min = 7  max = 7                                      
>  | |
>  |
>  |   Data Description:                                                     
>  |   | generated by r.mapcalc                                              
>  |    |
>  |
>  |   Comments:                                                             
>  |   | if(R_VannA at larsf == 1, 7, R_paramNew at larsf)                         
>  |    |
>
> 
> +--------------------------------------------------------------------------
>--+