Re: [ferret_users] contour labels

["William S. Kessler" <william.s.kessler@xxxxxxxx>]

Hi Xueli -

The contouring routines have an algorithm to avoid overlapping  
adjacent contours (a difficult thing to program, if you think about  
it). Further, contouring in done in subregions if the field is large  
(a legacy of code written for small-memory computers).

Thus, if the contour lines are very closely spaced, so labels would  
extend over an adjacent contour, they may be omitted. Try reducing the  
number of contours. (You can force this by doing your contouring in  
several steps using /OVERLAY with defined contour levels, say every  
third level overlaid 3 times - but you might end up with labels on top  
of each other.)

If the grid is very large, or very dense, then the subregions may be  
so small that there isn't enough room for the label. In that case, the  
grid is probably much denser than would be visible in a plot. Try  
subsampling the grid, e.g.:

contour my_variable[i=1:n:2,j=1:m:2]

You can also play with PPL CONSET, whose last argument is the distance  
between labels along a contour line:

PPL CONSET,,,,,,,,label_distance

This might work for a dense grid with subregions, but CONSET is very  
finicky - changes in the argument may do nothing, or may suddenly  
produce too many labels. Experimenting is necessary.

BK

On 19 Sep 2011, at 7:10 AM, wang wrote:

> Dear ferret-users,
>
> I use ferret to draw contour lines but it doesn't draw contour  
> labels. May be it due to the field is too messy.
>
> Do you know a way to force it to draw the labels.
>
> Thanks a lot!
>
> Xueli