On 4/16/2013 12:08 PM, Kevin wrote:
> I am trying to plot voltage values that have been sampled at 50 us
> intervals. Each of these samples have been timestamped so that they can
> be compared with other measurements. I've converted the timestamps to
> datenum values but when I use the PLOT function, the x-axis is scaled in
> such a way that all of my data is compressed to the centre of the plot.
> I have tried manipulating the axis using xlim and datetick but nothing
> changes. What I really need to be able to is zoom in on specific areas
> of the plot while safegaurding the timestamps and scaling the axis
> accordingly. Any advice would be much appreciated.
>
If you're coding in the absolute clock time to the us the problem is
that the resolution of DATENUM is being stretched to its limits. I just
tried here and the best I can get w/ xlim on the x-axis w/ a current
year datenum magnitude is roughly 10E-4 sec whereas the resolution of 1
ms on a datenum is otoo 10E0-8. Thus, while I could get a wider
vertical line than the default single pixel, it is still essentially a
vertical line.
If you need to also know the real time associated w/ that record I think
you'll have to keep that separate of the actual time record--I'd
probably just count the time series itself in us from wherever sample
starts in the record and then if need to date it write that as a text
string.
--![]()
> I am trying to plot voltage values that have been sampled at 50 us
> intervals. Each of these samples have been timestamped so that they can
> be compared with other measurements. I've converted the timestamps to
> datenum values but when I use the PLOT function, the x-axis is scaled in
> such a way that all of my data is compressed to the centre of the plot.
> I have tried manipulating the axis using xlim and datetick but nothing
> changes. What I really need to be able to is zoom in on specific areas
> of the plot while safegaurding the timestamps and scaling the axis
> accordingly. Any advice would be much appreciated.
>
If you're coding in the absolute clock time to the us the problem is
that the resolution of DATENUM is being stretched to its limits. I just
tried here and the best I can get w/ xlim on the x-axis w/ a current
year datenum magnitude is roughly 10E-4 sec whereas the resolution of 1
ms on a datenum is otoo 10E0-8. Thus, while I could get a wider
vertical line than the default single pixel, it is still essentially a
vertical line.
If you need to also know the real time associated w/ that record I think
you'll have to keep that separate of the actual time record--I'd
probably just count the time series itself in us from wherever sample
starts in the record and then if need to date it write that as a text
string.
--