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grdmath SUB operator #916

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arleaman opened this issue Feb 16, 2021 · 3 comments · May be fixed by #1527
Open

grdmath SUB operator #916

arleaman opened this issue Feb 16, 2021 · 3 comments · May be fixed by #1527
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feature request New feature wanted

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@arleaman
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grdmath SUB operator

I would like to use this feature to calculate residuals by finding the difference between two grid files.

Are you willing to help implement and maintain this feature? Yes, with guidance
@arleaman arleaman added the feature request New feature wanted label Feb 16, 2021
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@weiji14
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weiji14 commented Feb 17, 2021

Hi @arleaman, just need a bit more information on what your 'grids' are. Are they NetCDF files, xarray.DataArray/xarray.Dataset objects, or something else? This will help us to advice you a bit better.

About calculating residuals (using SUB), I would recommend doing it directly in xarray (see http:https://xarray.pydata.org/en/v0.16.2/computation.html#basic-array-math) using the minus '-' operator if possible, assuming that you are already familiar with xarray. Not to say we can't wrap a grdmath function in PyGMT, but the reverse polish notation of grdmath will make implementing this a bit tricky (though you are welcome to try).

@arleaman
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Thanks @weiji14 - I am using NetCDF files for my grids and will look into performing calculations in xarray.

weiji14 added a commit that referenced this issue Sep 19, 2021
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Wrap grdmath
2279eb5 
Initial commit for wrapping the grdmath function for #916
which is a "Raster calculator for grids (element by element)".
Original GMT `grdmath` documentation is at
https://docs.generic-mapping-tools.org/6.2/grdmath.html.
Implementation works by building and storing a computational
graph of the grid operations in a GrdMathCalc class object.
An output NetCDF grid or xarray.DataArray is produced
upon calling `.compute()` or by setting `outgrid=True`.
@weiji14 weiji14 linked a pull request Sep 19, 2021 that will close this issue
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@seisman seisman mentioned this issue Jul 20, 2023
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RFC: Wrap grdmath GenericMappingTools/pygmt
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@weiji14 @arleaman