[osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Jordi Torres]

Hi Bruno,


We also work with pointclouds in PointCloudViz ( www.pointcloudviz.com ) :)


2016-05-17 11:08 GMT+02:00 Bruno Oliveira <bruno.manata.oliveira at gmail.com>:

> I am rendering point clouds.
>
> What I want to do is to guarantee a certain point density is displayed. I
> know the number of points in each LOD and I know the bounding boxes of
> those LOD's. Can't I calculate a certain resolution value to pass to the
> LOD?
>
>
In the document I sent it states for PIXEL_SIZE_ON_SCREEN :
"The current screen-space extent that OSG uses in this mode is determined
by constructing a sphere that contains all of the model in question, then
3D projecting the diameter of the sphere into screen space and measuring
the diameter in pixels."

With respect to that it could be argued that a sphere projected in
ScreenSpace ( perspective ) is an ellipse so it has 2 diameters. Anyway
that measures are kind of orientative if you think in the major diameter it
will work. So you need to assign ranges to your LOD's based on this
assumption. You can try values ( i.e. from 500 to 1000 ) and tweak them
iteratively.

Anyway if you need a better understanding take a look to the traverse
method of PagedLOD node (
https://github.com/openscenegraph/OpenSceneGraph/blob/master/src/osg/PagedLOD.cpp#L125
)

Hope it helps.



> 2016-05-16 11:54 GMT+01:00 Bruno Oliveira <bruno.manata.oliveira at gmail.com
> >:
>
>> Thank you very much ! I understand very well the concept now, But I can't
>> still figure out a good range value, and based on what
>>
>> 2016-05-16 11:13 GMT+01:00 Jordi Torres <jtorresfabra at gmail.com>:
>>
>>> Hi Bruno,
>>>
>>> Take a look to this document from Chris ( Alphapixel )
>>> http://alphapixel.com/wp-content/uploads/2015/04/LOD-Level-of-detail-in-OpenSceneGraph-OSG.pdf
>>> .
>>> It could shed some light on LODding.
>>>
>>> Cheers.
>>>
>>> 2016-05-16 12:03 GMT+02:00 Bruno Oliveira <
>>> bruno.manata.oliveira at gmail.com>:
>>>
>>>> Hello,
>>>>
>>>> I am using a LOD but I don't understand how PIXEL_SIZE_ON_SCREEN range
>>>> mode works.
>>>>
>>>>
>>>> I am doing
>>>>
>>>> lod->setRangeMode(osg::LOD::RangeMode::PIXEL_SIZE_ON_SCREEN);
>>>>
>>>> but what parameters can I use to configure this mode?
>>>>
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>>>>
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>>>>
>>>>
>>>
>>>
>>> --
>>> Jordi Torres
>>>
>>>
>>>
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>>>
>>
>
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-- 
Jordi Torres
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