I suspect this has an easy answer, and is probably something I’ve already done (!), but the solution is eluding me. Everything, input/output, is in gridline registration. The starting oceanic input grid has a 0.2° resolution with -R-180/179.8/-89.8/89.8 bounds (1800x899). I need to transform it to…

[image] John_Geodesy: a grid with 0.25° resolution with -R-179.875/179.875/-89.875/89.875 bounds should it not be -R-179.75/179.75/-89.75/89.75 with 0.25 degree resolution and gridline registration? the “.875” decimal part seems off.

Not sure what it “should” be. I need to match this: mn_201810.grd: Gridline node registration used [Geographic grid] mn_201810.grd: Grid file format: nf = GMT netCDF format (32-bit float), CF-1.7 mn_201810.grd: x_min: -179.875 x_max: 179.875 x_inc: 0.25 (15 min) name: longitude n_columns: 1440 mn_2…

grdsample does not let extrapolate. That is, you cannot go from 179.8 to 179.875 -R-179.75/179.75/-89.75/89.75 is not global. It misses the poles and one column.

But the longitudes wrap around. How can I trick GMT to treat it that way? In other words, the column for longitude -180 should be the same as +180. I guess one could dump the original file with grd2xyz, copy the values for the -180 longitudinal column, paste it to the end of the file, while changin…

-179.875/179.875 is global at 0.25 and grid registration. It’s the same as -180/180 (same number of columns) and pixel registration. It’s just that you cannot do it with grdsample. Can’t follow what are the issues with the surface reinterpolation.

Background on the surface interpolation: The original grid (at 0.2° resolution) has invalid (NaN) values in non-land oceanic Arctic regions. Surface will interpolate values for every cell of a grid. It’s trivial to mask the land values. After interpolating with surface, how can the newly interpol…

Completing and re-registering a geographic grid

Q&A

mkononets July 17, 2024, 4:39pm 2

should it not be -R-179.75/179.75/-89.75/89.75 with 0.25 degree resolution and gridline registration? the “.875” decimal part seems off.

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Completing and re-registering a geographic grid

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