[GRASSLIST:930] RE: interpolation & shading problem/question

[John Gillette]

> The file mandes_.LI comprises N X Y Z values, where N is a 
> record ID that
> I'm omitting when I build the site file. The Z value is depth in
> meters, X & Y are long/latitude in decimal degrees.
> 
...
> 
> shade.rel.sh altitude=20 azimuth=270 elevation=andes5m
> 
>

shade.rel.sh takes a numerical derivative.  Your x,y location
is in degrees but your z data is in meters.

Does this cause the problem?  Do you need to re-project the data
to a meters coordinate system and then do the shading? Or perhaps
change the equations in shade.rel.sh to scale the derivative correctly?

Looking at the equations, x and y are divided by 8 * ewres() or 8 * nsres().

I don't know the answer.  Perhaps someone knows the answer to this?

John