Re: IDL plot is inconsistent, where is subtle error?

[Paul van Delst <paul.vandelst(at)noaa.gov>]

Lawrence Bleau wrote:
> 
> Hello, IDLers.  I'm having a very subtle problem with plotting from IDL.
> Either that or IDL is screwed up, which I doubt is the case.  First, my
> configuration:
> 
> IDL Version 5.2 (vms alpha)
> OpenVMS AXP V7.1-2
> 
> I'm plotting a set of values along the Y-axis (log plot), with time being
> on the X-axis.  The time is expressed as a double precision floating point
> quantity (created with DBLARR).  The time has a base year (time zero) of
> several decades ago, and I can't change this base year, so that's something
> I have to live with.  This is called an epoch time.  Typical values of an
> epoch time are in the range 357588000.D0.  I have a routine that converts
> from epoch time value to normal calendar notation (date and time).

IDL pre-v5.4 (or was it 5.3?) always plots in single precision (regardless if the data is
in double) so you can loose info when your numbers are that big.

What happens if you do a plot but subtract off the first value as an offset, something
like

  plot, epoch-epoch[0], values(*,k)

?

paulv

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