| Re: undefined keyword variables [message #17612 is a reply to message #17531] |
Mon, 01 November 1999 00:00   |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Dusting off my degree in horse-beating...
davidf@dfanning.com (David Fanning) writes:
>
> I think it is not only feasible, but required, that you
> provide default values for *any* variable you plan
> to use in the code. Certainly if I were planning to
> use the POSITION keyword I would have something like this:
>
> IF N_Elements(thePosition) EQ 0 THEN thePosition=!P.Position
> ...
> Plot, data, Position=thePosition
This doesn't always work. Here is what happens when I examine
!p.position after starting IDL fresh:
IDL> print, !version
{ alpha OSF unix 5.2 Oct 30 1998}
IDL> print, !p.position
0.00000 0.00000 0.00000 0.00000
That causes an error when I try to plot. Anyway, your solution takes
the previous plot position. I was interested in using the IDL default
position. I haven't found any logical way to figure that out. [ Okay,
there's the plot,/nodata,xstyle=5,ystyle=5 technique to set up the
coordinates ahead of time. Hmmm... ] I run into this situation where
I have two paths in my code, one path where I set the POSITION, and
one where I just want to pass the user's value. Check out map_set.pro
and map_struct_append to see what contortions RSI went through.
My point is that *whatever* strategy that IDL uses to pass undefined
keywords appears to be inconsistent. It should either be documented
or corrected.
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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