Re: Decimal digits in contour labels

[hankin@xxxxxxxxxxxxxxxxxxx (Steve Hankin)]

	**** Control over the spacing of contour labels ****

Hi Michel,

The PLOT+ program makes decisions to determine if there is adequate space for a
contour label. Its logic is based on the gradients within the field -- so that
if lines are densely packed or tightly curved it avoids placing labels in that
region. (As Billy Kessler says), this can (maddeningly) result in no labels at
all some times. It is particularly acute with noisy data.

My guess is that as you are increasing the number of decimals requested you are
also increasing the length of the formatted numerical string to be written
hence PLOT+ demands more room before it is willing to insert the label.

The magic argument that gives some control over this is a little goodie on the
CONSET command -- the "dslab" (delta arc length) which controls the nominal
spacing of contour labels (see page 12-4 of the PLOT+ Users Guide). The example
below illustrates.

	Happy Ferreting - steve

===============================================================

! default contour labeling
contour/i=1:20/j=1:20 (x^2 + y^2) ^ 0.5

! make the labels bigger
ppl conset .2
contour/i=1:20/j=1:20 (x^2 + y^2) ^ 0.5

! make the labels closer together    <== THIS IS THE KEY!
ppl conset .2,,,,,,,1
contour/i=1:20/j=1:20 (x^2 + y^2) ^ 0.5

! restore defaults
ppl conset .08,,,,,,,5

================================================================

On Aug 23,  4:30pm, beland@cerca.umontreal.ca wrote:
> Subject: Decimal digits in contour labels
> I tried to change the number of decimal digits in the contour label of a
> SHADE/LINE command and got unexpected results for some values.  Here is
> what I did:
>
> define axis/x=1:360:1 x360
> define axis/y=1:225:1 y225
> define grid/x=x360/y=y225 g360x225
> file /var=rho/grid=g360x225/format=UNFORMATTED/COLUMNS=`360*225` rho
> ppl shakey 1,1,0,0,-3
> shade   /line/key/i=1:360/j=1:225/levels=(1.0,1.035,0.001,3) rho
>
> The last argument in parenthesis in the /levels option should control
> the number of decimal digits.  Indeed it works as documented with
> -3,-1,0,1 and 2, but the contour labels disappeared if I used 3 or
> more, as if I had used -3.  How can I have contour labels with three
> decimal digits ?  The strange thing is that custom_contour_demo.jnl,
> given in the $FER_DIR/examples directory, does the same thing and it
> works...
>
> I tried to use PPL CONSET instead, with similar results.
>
> I am using Ferret 4.3 on a SGI Indigo running IRIX 5.3.
>
> --
> Michel Beland                 beland@CERCA.UMontreal.CA
> professionnel de recherche    tel: (514)369-5223  fax: (514)369-3880
> CERCA (CEntre de Recherche en Calcul Applique)
> 5160, boul. Decarie, bureau 400(423), Montreal (Quebec), Canada, H3X 2H9
>-- End of excerpt from beland@cerca.umontreal.ca




-- 

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Steve Hankin	|  7600 Sand Point Way NE  |  FAX (206) 526-6744
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