history plot "formula" cannot be used to scale up a plot

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Issue #308 new
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I plot several values, a voltage (range 0..1000 V) and a current (range 0..10 uA). With "formula" blank, the current is just a line at zero, it's range is too small. One has to click on it to see how it changes, and of course one cannot see what voltage changes correspond to the current changes.

On old history plots, I could use the "factor" value to change the scale of the current plot, so changes of both values could be seen on the graph. This worked well.

On the new history plots, this does not work well. If I set "Formula" to "500*x", sure I see both curves on the same plot, but the system now claims that my current is 500 uA, not 1 uA.

It looks like in addition to a "formula", we need the old "factor" and "offset" back to adjust the plots for best presentation of the data.

K.O.

Comments (2)

  1. dd1

    I know how I will fix this. First we apply the “formula”, this does arbitrary computations on the values, i.e. converts atmospheric pressure into air density. Then we apply factor and offset to position the value on the plot. Thus transformation of the value and positioning of the plotted value on the graph become separate again.

    ypixel = yoffset+yfactor*(formula(v) - voffset).

    for explanation of voffset, see https://bitbucket.org/tmidas/midas/issues/146/history-page-offset-needs-to-be-split

    offset and factor will need to be restored in the history plot editor, voffset will need to be added.

  2. dd1

    voffset will need to be added to the old history graph plotting code. In case where “formula” is blank, both old and new codes should produce similar plots. Old plotting code is still needed to look at history data at “months and years” time scale. K.O.

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