Re: XForms: downsampling data before plotting via xy_plot

From: Bill Unruh (
Date: Wed Mar 07 2001 - 14:45:12 EST

  • Next message: zaphodb: "Re: XForms: downsampling data before plotting via xy_plot"

    # To subscribers of the xforms list from Bill Unruh <> :

    On Wed, 7 Mar 2001, zaphodb wrote:

    > # To subscribers of the xforms list from "zaphodb" <> :
    > >
    > > > I've been using the xy_plot routine a lot and only recently I noticed
    > > > that when trying to plot a huge number of items in one window,
    > > > sometimes nothing is shown at all although it is apparent
    > > > that the window is refreshed.
    > > > I'm talking about plotting an audio signal as a waveform here.
    > >
    > > What's a "huge number?" By items, you mean points, I assume. Or do
    > > you mean overlays?
    > I mean in excess of 100.000 digitized audio sample points, no overlays.

    Yikes! (I presume this is the euopean notation where the decimal point
    is the division of the groups of three in a number). I certainly seems
    silly to plot this many points on a small graph ( max 1000 pixels-- this
    means 100 data points per horizontal pixel). Again, plot just the min and max of
    the 100 points, not all of them. I could well see the ploting algorithm
    going nuts trying to plot 100 vertical lines in one pixel width. (Does
    the internal array size in xyplot even allow for that many points?)
    Also if you are plotting in rapid succession, the screen can get erased
    befor all of the points have been plotted. So, is the plot static or are
    you constantly updating it?

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