| Re: PLOT procedure (was: Julian Day Numbers) [message #22597] |
Wed, 22 November 2000 00:00  |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Craig Markwardt wrote:
>
> James Tappin <sjt@star.sr.bham.ac.uk> writes:
>
>> One real gotcha with Julian day numbers is if you try to use them for a
>> time axis on a plot.
>>
>> It works fine for long time axes, but if you try looking at high-resolution
>> data things look really messy.
>>
>> The problem is that PLOT converts to single-precision before converting
>> coordinates to data and this means that all values are truncated to the
>> nearest quarter day (for IEEE floats).
>
> I agree that double precision plotting is important. Sometimes you
> just need it. However I think that in this case you really want to
> subtract a time offset anyway. Consider that your axis labels will
> never be pretty if you are using full Julian days. [ for those that
> don't know Julian days of this millenium number in the millions ].
> You can put in your XTITLE or TITLE the time offset and be done with
> it.
>
> Nit-pickily yours,
> Craig
>
> --
> ------------------------------------------------------------ --------------
> Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
> Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
> ------------------------------------------------------------ --------------
... but then again: what if you use the tickformat keyword with the
label_date function? I recently gave this a try and had to be careful
with roundoff errors (in IDL5.3).
Martin
--
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[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
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