I have accomplished this in the past using software un-related
to NCL. You can use a Perl script (or C/C++ program) and the
GD image libraries to open and ingest a JPG file, then open
a separate file (map background, streamlines, etc) as a PNG
file, then overlay the two and output a JPG or PNG file. More
details on the GD image library are found here:
and support for GIF had to be removed in recent years because of
the Unisys patent on LZW compression scheme. That isn't a problem
because you can always convert GIF to PNG.
I'd be pretty certain that the "ImageMagick" suite of tools
can also accomplish the same thing. If you search Google for
that tool-suite, I'm sure you can find it.
--Greg T. NCAR/RAP
> ----- Forwarded message from Addy Fu <addyfu AT hko.gov.hk> -----
> From: Addy Fu <addyfu AT hko.gov.hk>
> To: ncl-talk AT ucar.edu
> Cc: Addy Fu <addyfu AT hko.gov.hk>
> Subject: Plot Map with Image Background
> Dear Everyone,
> I have an idea to overlaying a map (e.g. streamline map) over an image
> (e.g. a satellite image in jpeg). Is it possible to load an image file
> and draw it with ncl?
> Thank a lot for your help.
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