Make it work: pscontour -Ccolor1,color2 -I about gmt HOT 10 CLOSED

Suspect the same is true in grdcontour. Note there are no z-values assigned here so what to contour? 0, 1, and 2? What do you think is good behavior here?

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Only place that z can come is from the selected contours them selfs, no? Hopefully that is not too late on the processing flow because we need to plot paint the image before the contours are drawn.

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Sorry, did not notice -A2. So if your data goes from 0 to 20 and you use -A2 and -C sets three colors there is a problem. I think we would need clean rules for how that may work, if at all.

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I am assuming that we would interpolate the colors into the number of required intervals. Something like what happens in grdimage lixo.grd -Cred,green -JX10 > lixo.ps, though this not an equivalent case.

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Let's define what should happen first. So in this case -C is either a master table (e.g., -Crainbow) or -Ccolor1,color2,...,colorn that defines a user "master" table, meaning the z-values in it are not the desired contour levels. Two cases:

1. -A is given. Then we calculate contour intervals from dataset min/max rounded to multiples of and sample the CPT accordingly.
2. No -A is given. We then arbitrarily decide on 10 contours from min to max as the default contours. Or perhaps we should compute a sensible rounded interval based on range? Nobody wants 7.37889, 9.3466, etc as the contours.

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BTW, this probably applies to grdcontour as well.

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I'm not sure it worth the trouble of doing 2. If min/max is [0.3 0.7] it will be hard to figure out a good contour interval that does not have many decimals.

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Well, we do this routinely with -Baf, but it is a bit different. Here, usually a log10 of the range, floored, then raising 10 to that power gives a decent interval, in this case 0.1. That gives n = 5 contours so we can check if n < 10 then double it. So n = 10 and 0.05. Not so bad for a default system when user dont care.

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Update: Both pscontour and grdcontour has this auto-contour settings. However, if you give a master cpt or a list of colors then presumably you want to color the contours using those colors. Thus the cpt will need to be resampled at the computer contour levels. This is not implemented yet.

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