[GRASS-user] r.mapcalc median filters entire map instead of onlynull values

[Patton, Eric]

Thanks for checking the script code, Glynn. I'm going to have to investigate what's going on locally on my machine.

~ Eric. 

-----Original Message-----
From: Glynn Clements
To: Patton, Eric
Cc: grassuser at grass.itc.it
Sent: 1/17/2007 3:23 PM
Subject: Re: [GRASS-user] r.mapcalc median filters entire map instead of onlynull values


Patton, Eric wrote:

> I'm trying to use r.neighbors and r.mapcalc in a script to fill holes
> in a raster where there are null values. A temporary raster is created
> with r.neighbors that contains a 3x3 median-interpolated surface of
> the primary DEM. r.mapcalc should only use the value in this temporary
> raster where a null value occurs in the primary DEM.
> 
> Here's the relevant section from my script:
> 
> # Procedure for filling nulls with multiple median filter passes
> 
> if [ "$PASSES" -gt 1 ] ; then
> 
>  COUNT=1
>  while [ "$COUNT" -le "$PASSES" ] ; do
> 					
>   r.neighbors --o input=${MAP} output=fill.tmp method=median size=3 
>   r.mapcalc "${MAP}_fill = if(isnull(${MAP}), fill.tmp, ${MAP})"
> 				
>   MAP=${MAP}_fill
>   COUNT=$(($COUNT + 1))
>   g.remove rast=fill.tmp 
> 
>  done
> 
> else
>  echo ""
>  r.neighbors --o input=${MAP} output=fill.tmp method=median size=3
>  r.mapcalc "${MAP}_fill = if(isnull("$MAP"), fill.tmp, "$MAP")"
>  MAP=${MAP}_fill
>  g.remove rast=fill.tmp 
> 
> fi
> 
> My problem is that when my script is run, the output $MAP_fill raster
> has it's entire surface smoothed with the median-filtered one, not
> just the null values like I intended. But if I run the r.neighbors and
> r.mapcalc lines in isolation outside of the script, I get the intended
> null-filled DEM with no unwanted smoothing.

FWIW, the above script (with PASSES=5 and MAP set to a test map) works
fine for me; the non-null cells remain untouched.

> Am I not quoting the r.mapcalc line properly?

No, both r.mapcalc commands are fine.

> FWIW, I've also tried different quoting methods for the r.mapcalc
> line, with the same problem occurring each time:
> 
> r.mapcalc ${MAP}_fill = "if(isnull($"MAP"), fill.tmp, $"MAP")"

This is bogus.

> r.mapcalc "${MAP}_fill = if(isnull(${MAP}), fill.tmp, ${MAP})"
> r.mapcalc ${MAP}_fill = "if(isnull($MAP), fill.tmp, $MAP)"

Either of these should work.

r.mapcalc simply concatenates all of its arguments, with spaces in
between. Usually, it's best to quote the entire expression with double
quotes.

You only need to use braces around a variable name if the substitution
is immediately followed by a character which is valid as part of a
variable name, e.g. ${MAP}_fill. Adding braces where they aren't
required is harmless.

-- 
Glynn Clements <glynn at gclements.plus.com>