[vtkusers] Add error bars to a 2D scatter plot

Marcus D. Hanwell marcus.hanwell at kitware.com
Mon Aug 20 16:02:37 EDT 2018

On Mon, Aug 13, 2018 at 2:20 PM Purves, Murray <purvesmh at ornl.gov> wrote:

> Hi,
> Is there a way to add error bars to scatter plot data using VTK? I am
> currently plotting point data using the C++ API; there is uncertainty
> associated with the data I am trying to plot which I would like to
> visualise also.
> I can't find any obvious references in the documentation to error bars;
> the only mention I have found is in a presentation at:
> https://na-mic.org/w/images/1/18/NA-MIC-VTK-Charts-2011.pdf, which
> doesn't seem to be a function that exists.
> Sample code snippet:
> // Chart source data is populated etc...
> vtkPlot* sampleScatter = chartXY->AddPlot(vtkChart::POINTS);
> sampleScatter->SetInputData(chartDataTable, 0, 1);
> // Here is where I would like to add the error bars -
> // below method is from the link, and does not work
> vtkPlotPoints::SafeDownCast(sampleScatter)->SetErrorArray(errorData.GetPointer());
> // Chart is rendered...
> where chartXY is a vtkChartXY object and chartDataTable is
> a vtkTable containing the x and y data in columns 0 and 1.
> Is there a way to populate error data for visualisation in a similar
> fashion to the above, or will I have to roll my own chart type?

I wrote those slides, and the code that generated them... I don't remember
how I did the error bars, I will see if I can dig it out, but I suspect it
was a feature that was never quite finished up. There weren't a lot of
people clamoring for error bars at the time, and we were busy adding lots
of things to charts.

It wouldn't be that much work to add as you suggest, I think my prototype
had a similar form, but I am not aware of any follow up work to complete
it. Recent VTK doesn't need Get/GetPointer either.
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