Re: [ferret_users] How to control contours interval?

["William S. Kessler" <William.S.Kessler@xxxxxxxx>]

Hi Goran -

It is possible to "influence" the number of contour levels ....  
"control" would be too strong a word. The pplus graphics code uses an  
algorithm to avoid contour labels overwriting contour lines, so where  
the lines are dense it omits labels. There are several interacting  
methods to influence the number of labels drawn, see the  
documentation for the qualifiers:

CONTOUR/SIZE/SPACING

Reducing SIZE and SPACING should get you more labels. In my  
experience, SPACING acts very non-linearly. Reducing the default 5  
(inches) makes little difference until somewhere between 2 and 3,  
then suddenly as the value is made smaller there will be many more  
labels.

Also note that if you are drawing the same contour lines over a FILL  
plot, it is not necessary to write out the CONTOUR command as you do  
here. Simply:

PPL CONTOUR/OVER

or do

FILL/LINE/KEY to get the whole thing in one command (note that FILL  
is an alias for CONTOUR/FILL)

Another useful method is to use few FILL levels (say no more than 7  
or 8), with a non-continuous key. Then overlay finer contour lines.  
The viewer can easily see the coarse, discrete color levels, then use  
the contours to distinguish the finer details.

A desperation move to get more labels is to overlay separate contour  
plots for each level. That thwarts the algorithm to prevent label  
overwriting, and the results may not be pretty, but it will produce  
more labels.

Billy K

On Nov 24, 2005, at 12:45 AM, Goran Georgievski wrote:

> Hello ferret users,
>
> Is it possible to have more control over labels used for contour  
> intervals?
> I have the following script for producing attached plot (please  
> have a look at
> the attached file: giants_pme_anom.gif)
>
> contour/fill/levels=(-1600,-800,200)(-800,-300,100)(-300,300,25) 
> (300,800,100)
> (800,1600,200)/key=continous/nolab/set_up pme-pme_ctrl
> ppl axlint,2,2
> ppl axlsze,0.2,0.2
> ppl shakey 1, 0, 0.14, 6, , , 1.15, 9.25, 0.5, 0.7
> ppl fill
> contour/size=.1/levels=(-1600,-800,200)(-800,-300,100)(-300,300,25)
> (300,800,100)(800,1600,200)del(0)/nolab/ov pme-pme_ctrl
> go land
>
> I have several anomaly patterns that I want to compare (values  
> spans from
> -1600 to 1600), but for the attached figure values spans form -250  
> to 250.
> However, altough values are in that range (-250, 250), when I plot the
> contour only labels for 25 and -25 isolines appear, even though I  
> used levels
> qualifier. I would expect that not only 25 levels are marked, but also
> 25,50,75 etc... How to do that?
>
> Thank you for your support,
>
> Goran
>
>
>
> --
> Goran Georgievski
> ICBM, Physical Oceanography (Theory), University of Oldenburg
> PO Box 2503, D-26111 Oldenburg, Germany
> Tel: +49-(0)441-798-4061, Fax: +49-(0)441-798-3404
>
>
>
> <giants_pme_anom.gif>