The -C cpt info says it should be in the units produced by the -Z option but you are using the original meters of the raw data
You are not making any allowance for the fact that grid nodes at higher latitudes represent less area than those at lower latitude. Use grd2xyz -Wa and +w in the histogram -Z option.
Hi Paul.
I had the -Wa option but I removed to see where is the problem. I will check the other option. I think that only could explain the upper graph.
For the middle graph I use makecpt to change the values.
However, I managed to get the image with the same code but in GMT6.1.1 (win64). So I suspect that there ir a bug in 6.2. I will check again.
We need a way to select either bin value or bin index to drive the color. I remember talking with @Joaquim but I did not implement. Given 6.1.1 the default should stay as that and then another switch or modifier selects bin index cpt
It seems it was modified here (#4373 and #4292). It was proposed: “Add modifier +b to -C when we want the CPT to apply to the bin’s x-value instead” but at the end it wasn’t implement it.