# [SciPy-User] Calculation of weights depending on area

Charles R Harris charlesr.harris@gmail....
Tue Aug 30 08:47:22 CDT 2011

```On Tue, Aug 30, 2011 at 4:01 AM, Andreas H. <lists@hilboll.de> wrote:

> Hi,
>
> again a question coming from analysis of geodata. Say, I have 3d
> (lat/lon/z) data, in the easiest case on a rectangular grid. Now I would
> like to re-grid these data to a new (again rectangular, in the simplest
> case) grid by calculating the volume-weighted mean of the original grid.
>
> So for each cell of the new grid, the algorithm should take the
> volume-weighted average of those grid cells from the first grid which "are
> part of" the new cell.
>
> Is there any algorithm in SciPy to do this? If not, do you have any
> suggestion on where to start? Perhaps there's some library from a more
> low-level language that could be wrapped?
>
> Any help is greatly appreciated :)
>
>
Sounds vaguely like the drizzle algorithm from astronomy. Another approach
would be to subsample and convolve, or smooth and resample. Choosing a
suitable method will depend on the smoothness/sampling of the original data.

For the original approach, if your sample points are on an evenly spaced
grid you can use an fft approach. The sampled data gives rise to a periodic
spectrum, multiplication by the transform of a rectangular spot gives the
data convolved by 'pillars', essentially subsampling in the Fourier Domain.

Or you can compute the overlaps as you originally proposed. I don't know of
any software for that but someone is bound to have done it before.

Chuck
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