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Re: PLOT question [message #22977 is a reply to message #22971]

Wed, 20 December 2000 10:51

Paul van Delst
Messages: 364
Registered: March 1997

Senior Member

Stuart Colley wrote:
>
> I have some data that is periodic, y=f(t) and the data is plotted as
> plot, t, y The problem is I'd like t to plot phase angle rather than
> time, the problem being the phase angle is between 0 and 1 and repeats.
> Attempting to plot the data you just get a plot between 0 and 1, what I'd
> like to be able to plot is each cycle of the data with it's phase angle.
>
> Any ideas on how to get the plot axes right?

If I understand you correctly, you want to remove the discontinuity in your phase angle - like in a
TAN plot that goes from +/- pi or +/- pi/2 ?

If so, one way is to calculate the phase angle derivatives. If there is a change in sign near a
known boundary (0 or 1), you can add or subtract (based on the sign of the derivative) the required
amount to make the phase angle curve continuous.

I did this many years ago in fortan to view the phase of radiometric signals from an interferometer.
They bounced between +/- pi and doing the above made the plot relatively (insert some hand-waving
here) continuous. If you have a noisy signal, then it can get a bit more difficult as the noise can
confuse matters when the signal is close to a boundary, i.e. you get a lot of flipping back and
forth, but then the result is a continuous curve with dropouts which, in some respects, may also be
a useful plot.

If this is not what you mean, then delete this message.

paulv.

--
Paul van Delst Ph: (301) 763-8000 x7274
CIMSS @ NOAA/NCEP Fax: (301) 763-8545
Rm.207, 5200 Auth Rd. Email: pvandelst@ncep.noaa.gov
Camp Springs MD 20746

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[Message index]

		Re: PLOT question By: Martin Schultz on Thu, 21 December 2000 09:44
		Re: PLOT question By: Jaco van Gorkom on Thu, 21 December 2000 06:05
		Re: PLOT question By: Stuart Colley on Thu, 21 December 2000 03:46
		Re: PLOT question By: davidf on Wed, 20 December 2000 16:40
		Re: PLOT question By: Craig Markwardt on Wed, 20 December 2000 16:14
		Re: PLOT question By: Craig Markwardt on Wed, 20 December 2000 16:01
		Re: PLOT question By: Paul van Delst on Wed, 20 December 2000 10:51
		Re: PLOT question By: Dave Greenwood on Wed, 20 December 2000 10:32
		Re: PLOT question By: davidf on Wed, 20 December 2000 10:16

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