[graph] 5D scatter plot

[ferdymercury]

Feature description

I wanted to propose an extension of the 4D scatter plot (xyz color) shown here:
https://root-forum.cern.ch/t/mark-different-regions-in-a-3d-scatter-plot/20501/5?u=ferhue

but using an additional column "size", which controls the size of the marker for each point.

Alternatives considered

• A TScatter2D deriving from TScatter would do the job, if there was an additional column for the Z coordinate, and if it could be drawn in 3D rather than a 2D map.

• TGraph2D with PCOLZ already does XYZ, but color == Z,
  so a TGraph3D could make color indepent of Z and TGraph4D the additional marker size.

Additional context

This feature works without problem in MATLAB, see https://fr.mathworks.com/matlabcentral/answers/1461764-5d-data-with-scatter3#answer_796239
as well as Javascript: https://plotly.com/javascript/3d-scatter-plots/

Example of the output:

[linev]

@ferdymercury

In principle, TGraph2D already provides set of x/y/z points. One only needs:

• optional color value for each point, which may be ruled by some palette
• optional size value for each point

One can create TGraph3D class derived from TGraph2D and managing such additional properties.
And I can implement them in JSROOT.

@ferdymercury - can you propose PR with TGraph3D class?

[couet]

TScatter2D might be the right approach. Internally, TScatter has a TGraph that holds the x and y coordinates, and TScatter adds the color and size dimensions, resulting in a 4D plot. The painting is handled by TGraphPainter. To achieve something similar and maintain the same naming convention, we could have a TScatter2D that holds a TGraph2D and adds the color and size dimensions, creating a 5D plot. The painting would then be handled by TGraph2DPainter.

[ferdymercury]

Thanks a lot for your replies!
TScatter2D sounds also reasonable to me, the problem is however that TGraph2DPainter assumes that all markers have the same size (and style), so TGraph2DPainter has to be modified accordingly, or a TGraph3DPainter class needs to be defined. I have currently limited time, so if someone wants to take over feel free!
otherwise I will definitely come back to this, but later this year.

[couet]

TGraph and TGraphPainter work similarly, where the PaintScatter method is handled by TGraphPainter. TScatter extends functionality by adding marker size and color, but the actual drawing is still done in TGraphPainter. Instead of inheriting from TGraph, TScatter contains a TGraph as a data member. The same structure should be applied for 2D:

TScatter2D should have a TGraph2D as a member.
The painting should be done in TGraph2DPainter::PaintScatter2D.
There's no need for a TGraph3DPainter.

[ferdymercury]

Thanks a million @couet for having implemented and merged TScatter2D.

I see only three remaining points in order to close this issue (or I can open a new one if you prefer):

• The z axis title is Z title;C title rather than just Z title if one does scatter->SetTitle("Scatter plot title;X title;Y title;Z title;C title"); [hist] TScatter2D palette title #20259
• If I hover the mouse over the x or y axis, I can scroll the mouse wheel and easily zoom or unzoom. However, over the z axis, this does not happen. Even if I right click and call SetRangeUser, nothing changes. Calling GetZaxis()->SetRangeUser from a script has no effect either.
• It would be nice that, if I hover the mouse over a data point (or if I right-click with the mouse or whatever you think it's best, to not mess up with the 3D rotation handle), the event status bar on the bottom of the canvas would show its information. See for example [graph] 5D scatter plot #16376 (comment) (but in the status bar, not in a popup).