matplotlib-users

[Matplotlib-users] re grid non regular data, then mask for continents / artifacts

[John [H2O] <was...@gm...>]

Hello,

I have a dataset that is provided with 0.5degree latitude information, but
1,2, or 10 degree longitude. I have used the matplotlib.mlab.griddata
function with natgrid installed to resample the dataset to a uniform 0.5x0.5
degree grid. 

The dataset locations can be seen below, note the regular lat spacing but
shifting lon spacing.

Now, the second plot below shows the raw data plotted. And the next the
regridded data. Note the artifacts. I have two requirements now for a data
mask. First, I need to mask any data over (under?) land, and secondly I need
to create a mask to get rid of the artifact data. Does anyone have a good
solution for this? Do I have to use something like the mlab.inside_poly
function? If so, how would I create the 'vertices' of the polygon?

I'm not looking for the landsea mask just for plotting, but I actually have
to mask the raw data array for writing out.

Could I use my original data to create the mask somehow? The problem is that
all the points between data locations would not be included.... 
Suggestions? Direct examples? It seems it must be a fairly common problem.

Raw data locations:
http://www.nabble.com/file/p24920704/datalocations_flat.png 

Raw data points plotted:
http://www.nabble.com/file/p24920704/rawdata.png 

Regridded data:
http://www.nabble.com/file/p24920704/regriddata.png 


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Re: [Matplotlib-users] re grid non regular data, then mask for continents / artifacts

[John [H2O] <was...@gm...>]

Impatiently I somewhat double posted (though, actually, I thought this was a
better list than scipy for the question). Regardless... the conversation is
mostly here:
http://www.nabble.com/2d-interpolation%2C-non-regular-lat-lon-grid-td24909685.html


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Re: [Matplotlib-users] re grid non regular data, then mask for continents / artifacts

[Christopher B. <Chr...@no...>]

John [H2O] wrote:
> Impatiently I somewhat double posted (though, actually, I thought this was a
> better list than scipy for the question). Regardless... the conversation is
> mostly here:
> http://www.nabble.com/2d-interpolation%2C-non-regular-lat-lon-grid-td24909685.html

One comment:

mgrid() is designed to interpolate form unstructured data to a regular grid.

Given  that your data is, in fact, quite structured, I suspect you may 
get better results from a a custom-written interpolator -- simple 
bi-linear (or bspline) interpolation would be pretty easy to write, and 
may give you a cleaner result. You may even be able to grab code 
straight from scipy.interpolate, an apply it on the different portions 
of your grid separately.

HTH,

-Chris




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Oceanographer

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