[GRASS-user] Raster surface from regularly spaced points

[Markus Metz]

You can try the overhauled v.surf.bspline module. You would need to svn 
up to get the new version, available in grass64 and higher.

run v.surf.bspline with the -e flag first to get estimated mean distance 
between points. If your points are not completely but almost regularly 
spaced, multiply the estimated distance by 1.5 and use that value for 
sin and sie.

BTW, method=bicubic gives much nicer results than method=bilinear.

To conserve the range of the original data, use a low lambda_i value 
somewhere between 0.01 and 0.1.

I would be really interested if it works for you!

Markus M



Luigi Ponti wrote:
> Hello,
>
> I have a grid of (almost) regularly spaced vector points from which I 
> would like to get a continuous raster surface. I say "almost" 
> regularly spaced, because the grid is almost square in that the 
> position of points derives from a netCDF grid with a different 
> projection than the current GRASS location. One cell of this 
> non-aligned grid covers several raster cells at the current region 
> resolution.
>
> So far I have been using a v.surf.idw approach but I am not sure 
> whether that is appropriate. An exact interpolator would be best, but 
> at least I want conserve the range of the original data.
>
> According the the GRASS book (p. 228), my options would be v.surf.idw 
> and v.surf.rst but the latter does not conserve data range, I think. 
> Another idea would be to use bilinear interpolation.
>
> Any hints very welcome and thanks for your attention if you got so far,
>
> Luigi
>
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