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Re: IDL5.2.1: Filling Contours on a Map Background
- Subject: Re: IDL5.2.1: Filling Contours on a Map Background
- From: "R.Bauer" <R.Bauer(at)fz-juelich.de>
- Date: Tue, 16 May 2000 09:20:53 +0200
- Newsgroups: comp.lang.idl-pvwave
- Organization: Forschungszentrum Juelich GmbH
- References: <firstname.lastname@example.org>
- Xref: news.doit.wisc.edu comp.lang.idl-pvwave:19608
> I am using some of scripts from a year ago before we upgraded to
> Before I was able to overlay filled contours atop a map background using
> the command:
> contour, value, longitude, latitude, /Fill, $
> background=white, /overplot , /Follow, $
> c_thick=1.5, nlevels=20, c_colors=ccolors, $
> levels=clevels, C_Charsize=0.5
> Where value, longitude and latitude are 2-D arrays of equal size.
> Have there been any unexpected changes?
I have learned to use always /cell_fill with maps.
Set this keyword to produce a filled contour plot using a "cell filling"
algorithm. Use this keyword instead of FILL when you are drawing filled
contours over a map, when you have missing data, or when contours that
extend off the edges of the contour plot. CELL_FILL is less efficient
than FILL because it makes one or more polygons for each data cell. It
also gives poor results when used with patterned (line) fills, because
each cell is assigned its own pattern. Otherwise, this keyword operates
identically to the FILL keyword, described below.
Tip - In order for CONTOUR to fill the contours properly when using a
map projection, the X and Y arrays (if supplied) must be arranged in
increasing order. This ensures that the polygons generated will be in
counterclockwise order, as required by the mapping graphics pipeline.
Warning - Do not draw filled contours over the poles on Cylindrical map
projections. In this case, the polar points map to lines on the map, and
the interpolation becomes ambiguous, causing errors in filling. One
possible work-around is to limit the latitudes to the range of -89.9
degrees to + 89.9 degrees, avoiding the poles.