The default line contouring algorithm should *not* create contour
lines that cross. Having contour spikes/cross-overs would be unexpected.
It is possible that if the 2D smoother is activated
(eg: res@cnSmoothingOn=True) then under unique circumstances
contour lines will cross, in particular, if the tension
resource (cnSmoothingTensionF) is set to some near zero number.
(see: http://ngwww.ucar.edu/ngdoc/ng/ref/hlu/obj/ContourPlot.res.html)
re: "another contouring algorithm"
I'm not sure about another algorithm. Actually, if needed,
I pass a light 2D smoother over the data. This means
any smoothing is under my control.
plot = gsn_...( wks, smth9_Wrap(data, 0.50, -0.25, True/False), res)
where the smth9_Wrap is a function in contributed that 'wraps'
the built-in smth9 function. The advantage of using smth9_Wrap
is that it returns all the meta data.
Either in default mode (no smoothing) or with smoothing
(res@cnSmoothingOn = True( you should not have to change your contour
levels or intervals. It only smooths the line (I think :-)).
re: GrADS and Cressman scheme
If Grads uses a Cressman scheme then this would be an implicit
smoother, would it not? The smoothing would be some function
of the scan radius. The larger the scan radius, the more the
smoothing.
Regards
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