Need help to add text and ruler to the vtk scene

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what is the best and proper way to add text and ruler to vtk renderer, I searched and found the closest one is How can i use the vtkActor2D? · Issue #1712 · Kitware/vtk-js · GitHub

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If you are just looking to add an SVG layer on top of your vtk.js scene without going through widgets, you can add an SVG element on top of your vtk.js scene, then use vtkPixelSpaceCallbackMapper to map 3D world coordinates to their corresponding 2D display location.
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Could someone give more hint or example how to “add an SVG element on top of your vtk.js scene” and how to use [vtkPixelSpaceCallbackMapper]?

Thanks!

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You have those two examples: