| Re: cgimage not generating output with cgps_open and cgps_close (fine in X window) . [message #89478 is a reply to message #89475] |
Mon, 20 October 2014 12:54   |
JTMHD
Messages: 9
Registered: October 2014
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Junior Member |
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On Monday, 20 October 2014 19:14:50 UTC+1, David Fanning wrote:
> David Fanning writes:
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>>
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>> David Fanning writes:
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>>> Well, leave the XSCALE and YSCALE keywords off your cgImage command.
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>>> They aren't needed (cgImage does this automatically), and they are
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>>> somehow (don't understand it yet) screwing things up.
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>>
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>> Alright, here is what is happening. This is a combination of the usual
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>> keyword inheritance nonsense, with a little twist from IDL letting you
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>> abbreviate keyword names.
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>> The proper way to set axis properties in cgImage is via the AXKeywords
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>> keyword, which no one can figure out how to use. So I allow a *limited*
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>> number of axis keywords to be used on the cgImage command line (e.g.,
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>> xrange and yrange). I don't forbid you to use XSCALE and YSCALE keywords
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>> (the ol' keyword inheritance problem), but there should be no reason to
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>> use them, either. cgImage knows what it is doing and does axis things
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>> correctly.
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>> Had you actually used XSCALE and YSCALE keywords, instead of their
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>> shorted form XS and YS, you would have received an error message, since
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>> these keywords are passed along to the TV command. They don't mean
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>> anything to the TV command, so the TV command complains. But, in their
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>> shortened form, XS and YS, they are interpreted by the TV command as the
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>> XSIZE and YSIZE keywords, and they will overwrite the XSIZE and YSIZE
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>> values cgImage uses internally to size a PostScript image. (The XSIZE
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>> and YSIZE keywords are only used by the TV command when in the
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>> PostScript device.) As a result, and this is why you weren't getting an
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>> error, your image was being sized to a one-by-one pixel, which was being
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>> displayed correctly in your output. :-)
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> By the way, when you write code like this:
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> cgimage, image, /xs, /ys
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> You are doing two things wrong in my opinion. You are abbreviating
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> keyword names, which makes your programs difficult to understand and
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> debug (see current discussion today), and you are using a keyword
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> shortcut that is inappropriate with non-boolean keywords that can have
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> values *other* than 0 or 1. It works, but it strikes me as a lousy
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> programming practice, since it, too, sends the wrong message to people
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> looking for problems in your programs.
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> Cheers,
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> David
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> --
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> David Fanning, Ph.D.
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> Fanning Software Consulting, Inc.
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> Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
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> Sepore ma de ni thue. ("Perhaps thou speakest truth.")
I see what you are saying and will bear it in mind. Its a hangover from using IDL interactively for a quick look at data, but I can totally see how this good practice would pay off if you where writing more sophisticated tools
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