[vtkusers] vtkCellPicker and "thin" objects

[Robert Dean]

Fixed my issue (a while ago, now remembering others may want to know the
solution), the indexing scheme I was using to map the clicked object back
into my data structure was flawed.  Basically, on all clicks after the
first click i had to subtract an index by 1.

On Thu, Sep 20, 2012 at 4:38 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Robert,
>
> The cell picker always chooses the object that is parametrically
> closest to, and that generally means that 3D cells will be picked
> before 2D cells, and 2D cells will be picked before lines, etc.  There
> is no simple fix without re-writing the picker code so that it
> prioritizes cells by dimensionality, i.e. points first, then lines,
> then faces, then 3D cells.  Likewise the picker could also be made to
> prioritize small (or thin) objects over larger objects, to allow e.g.
> a small pixel-sized facet to be picked even if it is surrounded by
> much larger facets.  Do you have any desire to look into
> vtkCellPicker.cxx to see what would have to be done?
>
>  - David
>
>
> On Thu, Sep 20, 2012 at 1:49 PM, Robert Dean <bob.dean at gmail.com> wrote:
> > Hello,
> >
> > I have two styles of actors in my scene. the first is a height map using
> 0.1
> > m square cells representing the world seen by a robot sensor. On top of
> this
> > I place planes representing detected walls.  Both the grid cells and
> walls
> > are drawn using triangle strips.  So the wall consists of a plane made
> up of
> > 4 points.
> >
> > With vtkCellPicker I can pick the cells in the height map with no
> > difficultly. But I can only select a subset of the walls.  I think the
> cause
> > is that the walls are planes, and therefore too skinny for the picker to
> > pick. I tried changing the picker tolerance, but it actually made the
> > problem worse.
> >
> > Does this logic make sense? I am tempted to render the walls as skinny
> boxes
> > to see if it makes a difference.
> >
> > -Bob
>
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