[GRASSLIST:4239] Re: GRASS 5.7.0 (2004) - v.surf.rst strange behaviour

[Paul Kelly]

Hello

On Tue, 24 Aug 2004, Javier A. Yebrin wrote:

> Hi all!
>
> I'm trying to interpolate a laser-altimeter survey in order to fill null
> areas. I've mainly followed by hand the procedure contained in the script
> r.fillnulls .
> The problem arises after the v.surf.rst module because the resulting
> elevation map is at a very first glance not correct: it looks like a ramp,
> the height values increasing linearly from North to South leading to absurd
> values such as 300000 meters at the bottom part...
> The lidar survey is a floating point map and it has been resampled to a
> 3mx3m grid.
>
> These are the steps:
>
> 1. Creating and growing a MASK for the null values
>
> r.mapcalc temp_raster="if(isnull(LIDAR))"
> r.grow in=temp_raster out=MASK
>
> 2. Vectorize the raster file: here i get a warning. Should i care?
>
> r.to.vect -v in=LIDAR out=temp_vector feature=point
> WARNING: Raster is not CELL, '-v' flag ignored, raster values will be
> written to the table.

I'm not sure if it's really necessary to do all those steps (vectorising 
etc.). If you run r.resamp.rst specifying the resolution to be the same as 
the current resolution, it should create a raster covering the current 
region but with the null areas filled in. You could then use it directly 
or use it to patch in the holes in the original raster. Perhaps it might 
be slow though; maybe that is the point in growing the MASK.

The steps would be something like:
g.region -p
*check what current ns and ew resolution are and use these in next step*
r.resamp.rst input=LIDAR ns=xx ew=xx elev=temp_smoothed
Use temp_smoothed as is or if you want the output to contain exactly the 
same values as the input in the non-null areas then just patch it in:
r.patch input=LIDAR,temp_smoothed output=interp_raster

Does this work?

Paul