[GRASS-user] strange behaviour of v.surf.idw

[Paul Kelly]

Hello Giovanni
On Tue, 12 Feb 2008, G. Allegri wrote:

> Hi Paul,
> are you still considering this post? If not I will try to dive in the
> algorithm by myself...

I'm definitely interested in helping you get to the bottom of the problem 
and improving GRASS with whatever useful information we find out. But I 
can't promise to give it any particularly urgent consideration - also I've 
been out all day and have just got home :)

I was waiting for you to answer the things I asked in my previous mail 
actually to see if they gave any more clues! I.e., can we see what the 
different maps look like when they all use the same colour table and also 
what did you mean by your concerns about the algorithm not managing 
something correctly.

Also, have you tried running using the -n flag (no indexing) and comparing 
the results. I think they should be the same for all regions then but 
might turn up something else interesting.

Hopefully when we have all this information available (command lines used 
too if you think they're relevant) we'll be able to see some kind of 
pattern emerging.

Also did you find my reference to the algorithm used (extract from my PhD 
thesis)? It should be in the mailing list archives of some old discussions 
of s.surf.idw/v.surf.idw if you search. I'll just go and dig it out again 
for you in case it's useful...
File /pub/users/paulk/grass/idw.ps.gz on ftp.qub.ac.uk (anonymous FTP).
It's gzipped PostScript - you'll need Ghostscript or similar to read it.

Paul