Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Robert Osfield]

Hi Bruno,

On 17 May 2016 at 14:23, Bruno Oliveira  wrote:
> Thank you both. The problem I'm having is relative to the point clouds
> density: too dense clouds will result in poor rendering performance if I
> tune my LOD to render sparser clouds. I can't find a good trade-off for the
> LOD resolution that fits both cases. I will probably subclass the LOD class.

Rendering very large point data clouds is specialist problem with very
specific needs compared to rendering traditional polygonal scenes.  To
get the best results for your particular problem then coming up with
custom approaches may well be best.

One trick I've used in the past with point clouds is to trade point
size for point density - this works well when the point clouds
represent surface data such as collected by radar or laser scanning of
3D objects or environments.  If you have normal and colour data using
point sprites can work really well at filling in the gaps between
points, which in turn means you can get away with lower point density
and still have a compelling visual.

Robert.
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Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Bruno Oliveira]

Thank you both. The problem I'm having is relative to the point clouds
density: too dense clouds will result in poor rendering performance if I
tune my LOD to render sparser clouds. I can't find a good trade-off for the
LOD resolution that fits both cases. I will probably subclass the LOD class.

Thank you once again.

2016-05-17 12:07 GMT+01:00 Robert Osfield :

> Hi Bruno,
>
> If you have some very specific metrics you'd like to use to choose LOD
> levels that aren't supported by the osg::LOD then you could subclass
> from osg::Group and implement your own Level of Detail behavior
>
> Robert.
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Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Robert Osfield]

Hi Bruno,

If you have some very specific metrics you'd like to use to choose LOD
levels that aren't supported by the osg::LOD then you could subclass
from osg::Group and implement your own Level of Detail behavior

Robert.
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Re: [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 :

> 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  >:
>
>> 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 :
>>
>>> 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.olive...@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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>>>
>>>
>>> --
>>> Jordi Torres
>>>
>>>
>>>
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>>>
>>>
>>
>
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-- 
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Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Bruno Oliveira]

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?

2016-05-16 11:54 GMT+01:00 Bruno Oliveira :

> 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 :
>
>> 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.olive...@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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>>>
>>
>>
>> --
>> Jordi Torres
>>
>>
>>
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>>
>
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Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Bruno Oliveira]

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 :

> 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  >:
>
>> 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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>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>
>>
>
>
> --
> Jordi Torres
>
>
>
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>
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Re: [osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Jordi Torres]

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 :

> 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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[osg-users] How does PIXEL_SIZE_ON_SCREEN work

[Bruno Oliveira]

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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