[GRASS5] Re: [GRASSLIST:8746] Re: r.fillnulls and res < 1

[Markus Neteler]

On Tue, Oct 25, 2005 at 02:11:33PM +1300, Hamish wrote:
> Robert:
> > > I am having trouble with r.fillnulls and a raster having a
> > > resolution of 0.48.
> > > 
> > > Is it right that r.fillnulls only works for raster with a resolution
> > > 1?
> 
> Markus:
> > thanks for finding the problem. I have fixed it in 6.1-CVS and
> > 6.0-CVS (for future 6.0.2).
> ..
> > Now resolution of 0.48 are accepted as well.
> 
> 
> Hey Markus,
> 
> -RES="`expr $nsres_int + $ewres_int`"  # avg*2
> +RES="`echo $nsres_int $ewres_int | awk '{printf "%f\n", ($1+$2) / 2.}'`"
> 
> 
> the buffer around the holes was twice the resolution on purpose. 

Hi Hamish,

it seems that I was too hasty:

Looking at cvs2cl.pl/Changelog:

2005-03-02 03:22  hamish
        * r.fillnulls: remove AWK for doing decimal multiplication -- broke
        when decimal point was a ",".  The buffer distance is pretty
        arbitrary anyway, so not a big deal if we lose sub-meter precision
        (I hope).

Note:
The decimal point story should be fixed due to the LC_.. statements
earlier.

> With nominally two points around the edge you interpolate into the hole with 
> a trained slope at the edges, otherwise you just get a flat plane.
> 
> Perhaps that should even be three times the mean resolution to give
> three points in all directions to define both the incoming slope &
> curvature. It shouldn't affect processing time any and hopefully would
> give a more realistic guess of what is in the hole. Maybe even a bigger
> buffer?

This sounds good to me.
 
> With just a single row of cells around the hole you often get gaps
> around the edges when distance > mean (.5 of the time? diagonals? worse 
> when ewres!=nsres).
> 
> 
> also,
> nsres_int="`g.region -gm | grep 'nsres=' | sed s/nsres=//`"
> ewres_int="`g.region -gm | grep 'ewres=' | sed s/ewres=//`"
> 
> could probably be reduced to:
> eval `g.region -gm`

Maybe you could fix it?

Markus