matplotlib-users

[Matplotlib-users] griddata and masked arrays

[ms <dev...@gm...>]

Hi,

I am trying to use griddata to plot some (irregularly) spaced data as a
contour plot, but sometimes ALL the grid it outputs is masked: so no plot.

In the docs I read:
"A masked array is returned if any grid points are outside convex hull
defined by input data (no extrapolation is done)."

but I have no real idea of what does it mean.
Any suggestion to troubleshoot / understand what's going on?

Thanks!

m.

Re: [Matplotlib-users] griddata and masked arrays

[Friedrich R. <fri...@gm...>]

2010/4/3 ms <dev...@gm...>:
> I am trying to use griddata to plot some (irregularly) spaced data as a
> contour plot, but sometimes ALL the grid it outputs is masked: so no plot.
>
> In the docs I read:
> "A masked array is returned if any grid points are outside convex hull
> defined by input data (no extrapolation is done)."
>
> but I have no real idea of what does it mean.
> Any suggestion to troubleshoot / understand what's going on?

When you do trinangulation, the lines between all pairs of points
define an inner region and an outer region, I guess, the inner region
is meant by "outside convex hull".

I furthermore guess, that all your interpolation points are outside
this hull, i.e., your interpolation spacing is of comparable order of
magnitude as your input data extent?

Friedrich