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Continuous colorbar

Question:

Is there a way to remove the the black lines in the colorbar of a shade or fill plot, so that I can get a smooth transition?

Example:

The default colorbar doesn't work well on plots with many levels. The black lines between levels make it hard to see the colors.

The above plot shows the default colorbar, produced by these commands:

     ! Define a variable ranging from 0 to 6
     ! and plot it in fine detail with the default colorbar

     yes? DEFINE axis/x=0:200:1 xax 
     yes? DEFINE axis/y=0:100:1 yax
     yes? LET var=6*(X[GX=xax]+Y[GY=yax])/300
     yes? FILL/LEV=(0,6,0.06)/TITLE="Default Colorbar" var  

Solution:

The simplest solution is the newer option /KEY=continuous for the KEY qualifier for color plot commands (FILL, SHADE, and POLYGON).

     yes? SHADE/I=15/J=10/KEY=CONT I+J

We keep this FAQ in place, as it shows how one might further customize a color key.

Save this script, ccbar.jnl which will be part of future releases of Ferret. It defines a viewport and fills that viewport with a shade plot of a variable that has the desired range of levels. Note that ccbar.jnl could easily be customized, for different size or style of labels, and so on.

!    GO ccbar x1 x2  y1 y2  v1 v2 dv  orient palette
 
!         x1 = x lo limit of rectangle for the colorbar
!         x2 = x hi limit of rectangle for the colorbar
!         y1 = y lo limit of rectangle for the colorbar
!         y2 = y hi limit of rectangle for the colorbar

!         v1 = lo value on colorbar 
!         v2 = hi value on colorbar
!         dv = delta value for clorbar axis
!
!         orientation = v for vertical or h for horizontal, default v
!         palette to use, optional

Where the first four arguments define a rectangle, as a fraction of the entire plot page. This is equivalent to how DEFINE VIEWPORT works. Its qualifiers /XLIMITS=x1,x2 and /YLIMITS=y1,y2 allow the user to specify a portion of the graphics window as the viewport.

Here is a simple example that calls ccbar.jnl.

     ! Replot the variable defined above, but hold off on the colorbar.
     ! First SET VIEWPORT, so that the key can be added as a viewport 

     yes? SET VIEW full       ! This holds the plot
     yes? FILL/LEV=(0,6,0.06)/TITLE="Continuous Colorbar Demo"/NOKEY var

     ! Plot the continuous colorbar, taking up the fraction of the window
     ! from  x=0.93 to 0.96, y=0.2 to 0.8, and showing levels from 0 to 6,
     ! with increments of 0.06.  Orient it vertically.

     yes? GO ccbar  0.93,0.96,  0.2,0.8,  0,6,0.06, v 

For more examples, in particular showing how to use the ccbar.jnl script when you are using viewports, see the demo, ccbar_demo