As an example of this projection we will create a gridded data set in polar coordinates using grdmath, a RPN calculator that operates on or creates grid files.
We will use grdcontour to make a contour map of this data. Because the data file only contains values with 2 =< r <= 4, a donut shaped plot appears in the example figure shown below.
using GMT G = grdmath("-R0/360/2/4 -I6/0.1 X 4 MUL PI MUL 180 DIV COS Y 2 POW MUL"); grdcontour(G, proj=:polar, frame=(annot=30, axes=:Ns, fill=:honeydew), cont=2, smooth=4, par=(FORMAT_GEO_MAP="+ddd",), show=true)
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These docs were autogenerated using GMT: v0.44.4