2D pointcloud plot using vtkActor

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1

In my application, I am displaying a 3D pointcloud view alongside a 2D overhead view of the same thing. For the 3D pointcloud, I am using a vtkActor and vtkPolyDataMapper with vtkTableToPolyData as input (I opted not to use vtkChartXYZ as I don’t want axes or a bounding box).

What would be the best way to display a 2D overhead view of the same pointcloud (ignoring the Z values)? I previously tried using vtkActor2D, but it seems to expect pixel coordinates from vtkPolyDataMapper2D. The best I’ve managed so far is to do a 3D view with vtkActor and disable all interaction, though that seems kind of hackish…

2

Your current approach is good. There is nothing hackish about it. It is a 3D data set that you want to show from a specific viewing angle. No need to disable all interactions, just disable rotation.

You can project all the points using transform polydata filter by setting a projection transform (e.g., set third column to zeros to project all points to z=0 plane). However, this is completely unnecessary and may make display worse, since you lose z ordering.

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  1. DeepCopy the vrkPoints from the 3D polydata.
  2. Loop through the new points and set the z component to a fixed value e.g. 0.0
  3. Create a new polydata and display it.
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@lassoan: Is there a way to simply disable the rotation? I’ve tried using the vtkInteractorStyleImage but it doesn’t let me pan around (I’m trying to zoom into the top right corner):

com-video-to-gif

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You can override actions by adding observers to GUI events. You can also implement your own interactor style class, derived from any existing style.

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6

That does seem unnecessary, though I figured there may be some kind of 2D plot mechanism using simple actors that would use less resources than a 3D plot. I had previously tried vtkChartXY for this and the plot looked fine, though I don’t really want/need the axes and other special features of that (and would prefersomething with an API similar to using a vtkActor for 3D plotting, just in 2D).

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2D plots still use 3D rendering under the hood because you still need 3D for example to manage z order of overlapping objects, be able to show widgets and handles with smooth 3D shaded surface, etc.

8

It still seems a bit wasteful to basically create a pair of renderers and actors that do the exact same thing, with the only difference being that one has a smaller window size and has interaction disabled. Is there something I’m missing?

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I’m not sure what pair of renderers you are referring to. Normally you create a renderer for each view. Usually you cannot share mappers and actors between views, but they may share processing pipeline and data objects.

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I’m talking about the renderer, actors, and mappers I’m creating for each view.

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You need to duplicate renderer, actor, mapper for each view, regardless of 2D or 3D.

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Given that, what would be the best way to implement multiple views of the same data that are updated in sync with the least duplication of resources?

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Hi @thully, I am actually trying to do exactly what you did about disabling Pan Zoom and Tilt of a vtkActor.
can you please share how you did that?
Thanks!