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

[Purves, Murray]

Thanks very much, anything you do find would be greatly appreciated – and if you can’t, any pointers you might have re: putting together a class would be fantastic as well.

Cheers

Murray



From: "Marcus D. Hanwell" <marcus.hanwell at kitware.com>
Date: Monday, August 20, 2018 at 16:02
To: "Purves, Murray" <purvesmh at ornl.gov>
Cc: "vtkusers at public.kitware.com" <vtkusers at public.kitware.com>
Subject: Re: [vtkusers] Add error bars to a 2D scatter plot

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