Re: overlaying raster over other fields

Thanks Daran,

I think that points me in the right direction. However, this "transparent"
color still ends up covering up what's below it. The missing value areas
are no longer white in the output ps file, but instead "transparent" (as
indicated by the light and dark gray checkerboard pattern using "display).
Using your input plus related stuff from ncl-talk archives, I have updated
the relevant attributes as follows:
  res@gsnDraw = False ; do not draw the plot since
stuff will later be overlaid
  res@gsnFrame = False ; do not advance frame
  res@cnFillOn = True ; Turn on color fill
  res@cnFillMode = "CellFill" ; Do not use RasterFill, as per
ncl documentation, transparency doesn't work with it
  res@cnLinesOn = False ; Don't use contour lines
(only fill)
  res@cnLevelSelectionMode = "ExplicitLevels" ; explicitly set the contour
levels
  ; make first value "missing" (-1 is the @_FillValue), then make the rest
of the values from min to max
  res@cnLevels =
array_append_record(-1,ispan(min_contour,max_contour,cntr_intrvl),0)
  ; use transparency as first color (-1 is transparent), then make the rest
of the colors from 3 to 101
  res@cnFillColors = array_append_record(-1,ispan(3,101,1),0)
  res@cnMissingValFillColor = -1 ; use transparency for missing value

Do you (or does anyone else) have any other suggestions?

Thanks again.

Joe

-----Original Message-----
From: Daran Rife [mailto:drife@ucar.edu]
Sent: Sunday, December 05, 2010 1:42 PM
To: Joe Grim
Subject: Re: overlaying raster over other fields

Hi Joe,

The value for transparent color is -1.

I believe you can simply set the cnMissingValFillColor to -1

res@cnMissingValFillColor = -1

See:

http://www.ncl.ucar.edu/Document/Graphics/Resources/cn.shtml#cnMissingValFil
lColor

If that doesn't work, try adding the -1 color to your color
map in the zeroth position. cnMissingValFillColor always
defaults to color 0 in your color table.

Daran

--
Good morning!
I was wondering if anyone could point me to any documentation  
explaining how
to do something?  I am currently trying to plot one field, and then  
overlay
a raster plot.  This is simple to do.  However, what is not simple is  
that I
would prefer to only plot non-missing raster data points, and be able  
to see
what was plotted below where the raster field is missing.  Currently,  
the
missing values are plotted as white and covers over the lower-laying  
field.
The only way I can think of accomplishing this would be to plots  
thousands
of teeny polygons instead of the raster plot, but this would be very
inefficient (and require a lot more coding.)  Would anyone be able to  
help
me find an easier way here?
Thank you very much!
Joe Grim
_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk