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*Subject*: Re: PLOT procedure (was: Julian Day Numbers)*From*: Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>*Date*: 21 Nov 2000 22:57:48 -0600*Newsgroups*: comp.lang.idl-pvwave*Organization*: U. Wisc. Madison Physics -- Compact Objects*References*: <3A1145DA.605789C4@tidewater.net> <8ve790$gk6$1@usenet.bham.ac.uk>*Reply-To*: craigmnet(at)cow.physics.wisc.edu*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:22308

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 --------------------------------------------------------------------------

**Follow-Ups**:**Re: PLOT procedure (was: Julian Day Numbers)***From:*Martin Schultz

**References**:**Julian Day Numbers***From:*Ben Tupper

**PLOT procedure (was: Julian Day Numbers)***From:*James Tappin

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