[vtkusers] Noise appears when extreme zooming in

Ken Martin ken.martin at kitware.com
Tue Oct 18 08:49:08 EDT 2016


Are you zooming using one of VTK's interactor styles? or are you explicitly
calling zoom or dolly on the camera?  Using dolly() the distance on the
camera should be changing and as you noticed it isn't.

Since you mentioned you have coincident geometry that can be an issue. When
you have two polygons at the same location the rendering process can result
in a random determination of which is on top. If the coincident geometry is
in two different mappers you can use the

void SetRelativeCoincidentTopologyPolygonOffsetParameters(
    double factor, double units);

method to move one of the mappers slightly in front of the other.





On Tue, Oct 18, 2016 at 1:01 AM, Patricio Palma C. <patriciop at gmail.com>
wrote:

> Hi Ken, experts,
>
>    Thank you for the quick response.
> Regarding point one, SetDiffuse(0.0) was applied to all actors, the
> structure looks darker with no shadows, but the issue still occurs.
>
> About point 2:
> - the actor we use is derived from vtkQuadricLODActor
> - and there are some overlapping geometries
>
> Below is a image of the structure in the beginning. Clipping range,
> position, focal point and distance are shown below
> [image: Inline image 1]
> Debug: Camera clipping range:  3.61282   4.44839
> Debug: Camera position:  -1.93487   2.37646   2.48559
> Debug: Camera focal point:  0.0543755   -0.0598546   0.0492757
> Debug: Camera distance:  3.97849
> Debug: Bounds : [  -0.100974  ,  0.296875  ,  -0.08  ]  [  0.08  ,  0  ,
>  0.05  ]
>
> After zooming in a bit, it appears a soft pattern of lines over the face
> of the structure
> [image: Inline image 2]
> Debug: Camera clipping range:  3.61282   4.44839
> Debug: Camera position:  -1.92875   2.37186   2.4952
> Debug: Camera focal point:  0.0604954   -0.0644594   0.0588774
> Debug: Camera distance:  3.97849
> Debug: Bounds : [  -0.100974  ,  0.296875  ,  -0.08  ]  [  0.08  ,  0  ,
>  0.05  ]
>
> Finally after zooming in a couple of steps more, it appears noise/lines
> over the face.
> [image: Inline image 3]
> Debug: Camera clipping range:  3.61282   4.44839
> Debug: Camera position:  -1.92882   2.37202   2.49498
> Debug: Camera focal point:  0.0604254   -0.0643013   0.0586621
> Debug: Camera distance:  3.97849
> Debug: Bounds : [  -0.100974  ,  0.296875  ,  -0.08  ]  [  0.08  ,  0  ,
>  0.05  ]
>
> It calls my attention that only position and focal point are being updated
> after zooming in.
>
> Thanks
> Patricio
>
> On Mon, Oct 17, 2016 at 8:21 PM, Ken Martin <ken.martin at kitware.com>
> wrote:
>
>> It could be a few things, we would really need more details to narrow it
>> down. Two things you can check
>>
>> 1) maybe a lighting issue, if you change your actors to be only ambient,
>> no diffuse, do you still see the issue?
>>
>> 2) maybe a zbuffer issue, If you zoom too far you can end up with bad
>> (not ideal) zbuffer clipping ranges. To narrow that down
>>  - are these Actors or Actor2D, what mapper are you using,
>> ​​
>> do you have overlapping or coincident geometry?
>>  - when you see the problem what is the value of
>> ​​
>>     - the camera's clipping range
>>     - camera's position, and focal point, distance
>>     - the bounds of your data
>>
>> Generally you do not want any of those values to be really small or large
>> relative to the square root of the range a float can normally hold.
>>
>>
>>
>>
>>
>> On Mon, Oct 17, 2016 at 5:28 PM, Patricio Palma C. <patriciop at gmail.com>
>> wrote:
>>
>>> Hi experts, does anybody has any idea of what could causing the issue
>>> described in the previous email?
>>> Recently I have noted that something similar occurs on 3D
>>> structures when zooming in extremely to the structure and then rotating it.
>>> It appears a kind of pattern to generate the shadow of the face but as you
>>> rotate the structure the face begin to get noisy.
>>>
>>> My current setup is VTK git development branch using OpenGL2 as
>>> rendering backend. mesa 12.0.1 with AVX. I have also tried using mesa 11.2
>>> and the results are the same.
>>>
>>> Thanks!
>>> Regards
>>> Patricio
>>>
>>> El Monday, October 3, 2016, Patricio Palma C. <patriciop at gmail.com>
>>> escribió:
>>>
>>>> Dear Experts
>>>>
>>>> I'm using VTK 7.1 (latest Git version) and Mesa 12.0 with AVX. I have
>>>> an application that display a 2D structure and some data on it. After
>>>> zooming in a couple times in the same spot of the structure it begins to
>>>> appear some noise over the 2D structure that increase after continuing
>>>> zooming in.
>>>>
>>>> Is this a known issue? is there a way to solve/avoid this?
>>>>
>>>> I've attached some pictures showing how the noise appears while zooming
>>>> in.
>>>>
>>>> [image: Inline image 2]
>>>> [image: Inline image 3]
>>>> [image: Inline image 5]
>>>> [image: Inline image 6]
>>>>
>>>> --
>>>> Patricio Palma Contreras
>>>>
>>>
>>>
>>> --
>>> Patricio Palma Contreras
>>>
>>>
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>>
>>
>> --
>> Ken Martin PhD
>> Chairman & CFO
>> Kitware Inc.
>> 28 Corporate Drive
>> Clifton Park NY 12065
>> 518 371 3971
>>
>> This communication, including all attachments, contains confidential and
>> legally privileged information, and it is intended only for the use of the
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>> destroy the original message.  Thank you.
>>
>
>
>
> --
> Patricio Palma Contreras
>



-- 
Ken Martin PhD
Chairman & CFO
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065
518 371 3971

This communication, including all attachments, contains confidential and
legally privileged information, and it is intended only for the use of the
addressee.  Access to this email by anyone else is unauthorized. If you are
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