[GRASS-user] DEM, natural neighbor interpolation and Grass

[Maciek Sieczka]

Hi!

Maybe some of you remember my notes about the nnbathy (a natural
neighbor interpolation program), it's usability for producing DEMs from
clustered, heterogenous input and it's complicated interaction with
Grass.

nnbathy performs great. Now I wrote a script which is an easy to
use interface between nnbathy and Grass. All you need to do to run it
is to specify the input raster name and the output name. The script will
transform your input into x,y,z which nnbathy accepts, let nnbathy
interpolate the grid, then let awk do the processing from x,y,z nnbathy
output into Grass ASCII raster, and, finaly, r.in.ascii imports.

Please take a look at it and let me know what you think (also about the
html man page). I'll be putting the script on WIKI in few days if
nobody minds.

In order to obtain nnbathy with serial input processing enabled (to
interpolate any large grid with minor memory usage), please compile
it yourself following the instructions in the man page. The prebuilt
binaries at http://www.marine.csiro.au/~sakov don't have serial input
processing turned on.

Cheers
Maciek

P.S.

Please note that nnbathy accepts quite few options which modify the way
the output is produced. I have set the following ones in my script:

'-W 0' which limits the output non-NULL area only to the convex hull
encompasing the input data. You could let nnbathy extrapolate if
you need to, by modyfing the number after -W.

'-P alg=nn -n' which chooses the Sibson natural neighbor interpolation
algorithm. However, other 2 are possible - non-Sibsonian natural
neighbor, and linear (which looks exactly the same as the triangulation
eg. in Saga).

I haven't implemented controlling any nnbathy options through my
script, because for DEM production I'm most happy with output produced
by those particular settings I hardcoded. I guess you should be happy
with the result too.

There are several more options in nnbathy, if you want to experiment
the script is easy to modify. Please consult with nnabthy help page to
learn more.

Maciek


--------------------
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