[vtkusers] vtkPicker picks an actor that isnt remotely close to the pick point

[John Eke]

Thanks a lot! That worked. What I need is for there to be no tolerance AT ALL, regardless of the size of the render window. Is there a fixed value I can set for this effect? I tried zero, and that didnt work.

- John E




________________________________
From: kent williams <nkwmailinglists at gmail.com>
To: John Eke <tonee47 at yahoo.com>
Cc: vtkusers at vtk.org
Sent: Thursday, May 28, 2009 2:32:21 PM
Subject: Re: [vtkusers] vtkPicker picks an actor that isnt remotely close to  the pick point

the vtkPicker class lets you set the tolerance, for picking.  The
default tolerance is apparently a bit too loose for your taste.

>From the documentation:

> virtual void vtkPicker::SetTolerance(double)     [virtual]
>
> Specify tolerance for performing pick operation. Tolerance is specified as fraction of rendering window size.
> (Rendering window size is measured across diagonal.)

The way this works is a little squirrelly, because you probably care
about a maximum distance from the exact pixel center, in pixels.  But
this function wants a fraction of the window size (as measured
diagonally), which you'll have to compute based on the window
geometry.  And if your window can be resized, you'll have to watch for
resize events and update the picker tolerance.

But the reason you can pick a few voxels away from the particular
voxel is that it's tricky to pick small features with the mouse
pointer.  If you set the tolerance too low, it will make it rough for
users to pick anything.

On Thu, May 28, 2009 at 9:02 AM, John Eke <tonee47 at yahoo.com> wrote:
> Hi Guys,
>
> I have a scenario where I am trying to enable annotations on images
> displayed in a vtkImageActor. When I click on the image, I place a small
> marker at that point on the image. Now when I click on that marker, it
> allows me to do other things like enter notes etc.
>
> Problem is, I use vtkPicker to do the pick, and when I click on the marker
> it works, problem is I move several pixels AWAY from the marker and when I
> attempt a pick, I still pick the same marker. It seems the markers have a
> few pixels around them where if you click, you can still pick the actor. IS
> there any way to change this? Are there any params in vtkPicker I can set to
> make sure that the markers should ONLY be picked if the intersect DIRECTLY
> with the pick point?
>
> Thanks
>
> John E
>
>
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