[vtkusers] VtkVolumePicker choosing the edges of my volume

[David Gobbi]

It requires and isovalue.  Not an isosurface.

Specifically it requires the same isovalue you would use to create the
isosurface.  But it doesn't require an isosurface.

Or looking at it another way, the isosurface for a particular isovalue
exists as a platonic idea even if you don't generate it.  Though I
don't know if that helps my explanation at all.

 - David

On Thu, Mar 14, 2013 at 12:41 PM, Doug Hoppes <dhoppes at mbfbioscience.com> wrote:
> Thanks for the response.
>
> That was the function that I was using.  However, how do you determine the isovalue of the surface without creating an isosurface?
>
> Essentially what I would need is the list of the pixels that would be along the line of the camera position and where I picked on the screen.
>
> Doug
>
> -----Original Message-----
> From: David Gobbi [mailto:david.gobbi at gmail.com]
> Sent: Thursday, March 14, 2013 2:36 PM
> To: Doug Hoppes
> Cc: vtkusers at vtk.org
> Subject: Re: [vtkusers] VtkVolumePicker choosing the edges of my volume
>
> The picker has a method called SetVolumeOpacityIsovalue() that allows you to select an isovalue for picking.  As the documentation states:
>
>   "If you want to do the pick based on an actual data isovalue rather than
>    the opacity, then pass the data value through the scalar opacity function
>    before using this method."
>
> So if you know the isovalue, then use the volume's opacity transfer function to find the corresponding opacity.  Then call SetVolumeOpacityIsovalue().
>
>  - David
>
> On Thu, Mar 14, 2013 at 11:25 AM, Doug Hoppes <dhoppes at mbfbioscience.com> wrote:
>> Hi all,
>>
>>
>>
>>                 Okay, not sure what is going on here.  I have an image
>> stack that is pretty dark with a semi-white blob in the center.  I
>> would like to be able to select any point on that blob.
>>
>>
>>
>>                 I find that I can do this, if I turn the pickable
>> setting of the volume off, and create an isosurface for the semi-white
>> blob.  However, ideally, I would prefer to just use the
>> vtkVolumePicker to select the blob, rather than having to spend the time creating the isosurface.
>>
>>
>>
>>                 When I try to click on the white area of the blob, I
>> always get the edges of the volume.  Is there a way to ignore the
>> volume's dark areas?  Since I don't know what the exact pixel values
>> are, is there a way to define a range of pixels to ignore (i.e. ignore
>> all pixels < 10 and pixels > 100)?
>>
>>
>>
>> Doug
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