[vtkusers] vtkClipClosedSurface using a finite plane

[sebastian ordas]

I understand. I will try a pipeline for clipping in sequence

let´s see how it goes
thanks


On 6/15/2012 7:54 PM, David Gobbi wrote:
> On Fri, Jun 15, 2012 at 4:31 PM, sebastian ordas
> <sebastian.ordas at gmail.com>  wrote:
>> thank you David
>>
>> yes, more planes, more contours ... I thought the planes would set like a
>> region inside which the clipping is performed
>>
>> anyway ... i will continue thinking ...
>>
>> btw, do you think it´s doable the modification in
>> vtkClipClosedSurface::ClipAndContourPolys() to achieve my requirement?
> Doubtful.  It really expect the scalars to provide the signed distance
> from an infinite plane.  If given the signed distance from any other
> kind of surface (especially one with sharp corners, like a box) it
> won't give good results for the contours.
>
> To put this in more general terms, the use of clipping scalars in a
> clipping algorithm assumes that the clip surface is flat, or nearly
> flat.  The clipping scalars give a piecewise linear approximation of
> the clipping surface.  Using clip scalars to clip with anything but a
> plane will only give approximate results.  As the curvature of the
> clip surface increases, the approximation becomes worse.  Corners are
> points of infinite curvature... so you can see where this is going.
>
> Clipping away the outside of a box can be done by clipping with each
> of the six planes in sequence.  Clipping away the inside of a box
> cannot be done in this way.
>
>   - David
>
>
>> Alternatively, If as a preprocessing step I clip my scene e.g. with a
>> sphere, then I will get open surfaces ..... that will affect
>> vtkClipClosedSurface, right?
>>
>> just the first thoughts ...
>>
>> let me know if you come out with some idea
>>
>> thanks again,
>> sebastian
>>
>>
>>
>> On 6/15/2012 7:16 PM, David Gobbi wrote:
>>> Hi Sebastien,
>>>
>>> It's not possible to limit the plane size with vtkClipClosedSurface.
>>> The planes are always infinite in extent.  Adding more clipping
>>> planes will always clip away more of the data, never less.
>>>
>>>   - David
>>>
>>>
>>> On Fri, Jun 15, 2012 at 4:10 PM, sebastian ordas
>>> <sebastian.ordas at gmail.com>    wrote:
>>>> Dear all,
>>>>
>>>> I'm successfully using vtkClipClosedSurface in an application for slicing
>>>> a
>>>> set of perfectly closed meshes.
>>>>
>>>> Now I would like to cut through my scene with a finite plane or somehow
>>>> restrict the slicing extension to a given extent
>>>>
>>>> My target  application is an ultrasound simulator. I would like to avoid
>>>> slicing through the complete scene (i.e all organs in my scene) but
>>>> within
>>>> the US image plane only
>>>>
>>>> I´m trying to combine several planes in vtkClipClosedSurface, but I´m not
>>>> getting the pretended results
>>>>
>>>> Any hint will help
>>>>
>>>> many thanks
>>>> sebastian