[osg-users] How can I get the viewer's camera to 'ignore' a node's geometry?

[Preet]

Hey,

By default some of the parameters of a camera are computed based on
the contents of a scene (like the near and far plane). Camera
manipulators will also behave differently based on the placement of
objects in the scene. I have one node in my scene that I want the
camera and any manipulators to 'ignore' in this respect, but I still
want the node to be rendered. Is there anyway I can do this?

Preet
_______________________________________________
osg-users mailing list
osg-...@lists.openscenegraph.org
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org

[Chris Hanson]

On Thu, Oct 4, 2012 at 12:48 PM, Preet <prismati...@gmail.com> wrote:

By default some of the parameters of a camera are computed based on
the contents of a scene (like the near and far plane). Camera
manipulators will also behave differently based on the placement of
objects in the scene. I have one node in my scene that I want the
camera and any manipulators to 'ignore' in this respect, but I still
want the node to be rendered. Is there anyway I can do this?

Probably not. The nodes have to be Culled in order to be added to the Render List, and the scene bounds and such are computed during culling.

The bigger question is what are you trying to do, and why? That answer will probably allow us to suggest something useful, like depth partitioning or something.

 

 

-- 

Chris 'Xenon' Hanson, omo sanza lettere. Xe...@AlphaPixel.com http://www.alphapixel.com/

Training • Consulting • Contracting

3D • Scene Graphs (Open Scene Graph/OSG) • OpenGL 2 • OpenGL 3 • OpenGL 4 • GLSL • OpenGL ES 1 • OpenGL ES 2 • OpenCL

Digital Imaging • GIS • GPS • Telemetry • Cryptography • Digital Audio • LIDAR • Kinect • Embedded • Mobile • iPhone/iPad/iOS • Android

[Preet]

On Thu, Oct 4, 2012 at 3:52 PM, Chris Hanson <xe...@alphapixel.com> wrote:
> On Thu, Oct 4, 2012 at 12:48 PM, Preet <prismati...@gmail.com> wrote:
>>
>> By default some of the parameters of a camera are computed based on
>> the contents of a scene (like the near and far plane). Camera
>> manipulators will also behave differently based on the placement of
>> objects in the scene. I have one node in my scene that I want the
>> camera and any manipulators to 'ignore' in this respect, but I still
>> want the node to be rendered. Is there anyway I can do this?
>
>
> Probably not. The nodes have to be Culled in order to be added to the Render
> List, and the scene bounds and such are computed during culling.
>
> The bigger question is what are you trying to do, and why? That answer will
> probably allow us to suggest something useful, like depth partitioning or
> something.
>

I'm trying to visualize stuff like buildings and roads on the surface
of the Earth. But for reference, I'd also like to display the surface
of the Earth (just as a set of points). Including geometry for the
Earth's surface makes the other stuff disappear (and reappear at
certain angles). To me it looks like an issue with the near/far planes
of the frustum.

I wanted to avoid specifying the near/far planes manually since the
behaviour without the Earth surface geometry is perfect as is. I don't
care about the overhead of drawing the surface geometry since its so
simple, and I don't want the scene graph to account for the surface
geometry (outside of rendering it); the other objects in the scene
should determine the camera frustum.

[Chris Hanson]

I wanted to avoid specifying the near/far planes manually since the

behaviour without the Earth surface geometry is perfect as is. I don't
care about the overhead of drawing the surface geometry since its so
simple, and I don't want the scene graph to account for the surface
geometry (outside of rendering it); the other objects in the scene
should determine the camera frustum.

  Due to the way OGL works with near/far, if you want it drawn, you need it taken into account when computing the near/far planes.

  Are you just worried about the far plane being set too far?

  > Including geometry for the

Earth's surface makes the other stuff disappear (and reappear at
certain angles). 

  It sounds to me like you're not trying to solve the right problem. You should first determine WHY these other items aren't displayed at times.

[Preet]

On Thu, Oct 4, 2012 at 5:37 PM, Chris Hanson <xe...@alphapixel.com> wrote:
> I wanted to avoid specifying the near/far planes manually since the
>>
>> behaviour without the Earth surface geometry is perfect as is. I don't
>> care about the overhead of drawing the surface geometry since its so
>> simple, and I don't want the scene graph to account for the surface
>> geometry (outside of rendering it); the other objects in the scene
>> should determine the camera frustum.
>
>
>
> Due to the way OGL works with near/far, if you want it drawn, you need it
> taken into account when computing the near/far planes.
>
> Are you just worried about the far plane being set too far?
>
> > Including geometry for the
> Earth's surface makes the other stuff disappear (and reappear at
> certain angles).
>
> It sounds to me like you're not trying to solve the right problem. You
> should first determine WHY these other items aren't displayed at times.
>

Sorry if it wasn't clear; the items aren't being displayed because the
near and far planes that osg sets creates a frustum that doesn't
include them. I need to manually set the near and far planes to see
everything.

The near and far planes that osg sets without the earth surface
geometry is fine. Once you add the surface geometry though, the near
and far planes are set such that the items are no long in the view
frustum.

I was looking for a flag or something that basically tells osg "hey,
don't include this node when you do your view frustum calculations"

[Sergey Polischuk]

Hi

You can set ComputeBoundingBoxCallback on a geometry to specify whatever bounds you want. In your case to ignore earth geometry bound you can set its bound to uninitialized bounding box, and it will not make any difference to near\far calculations. Note that this thing completely disable view frustum culling on a geometry! In order to get it working you should write your cull callback and do check vs actual bounds there, if you need it.

Code looks like:

class UseInitialBoundsCallback : public osg::Drawable::ComputeBoundingBoxCallback
{
public:
osg::BoundingBox computeBound (const osg::Drawable & drawable)
{
osg::BoundingBox brand_new_uninitialized_bbox;
return brand_new_uninitialized_bbox;
}
};

geometry->setComputeBoundingBoxCallback(new UseInitialBoundsCallback);

Cheers, Sergey.

05.10.2012, 05:11, "Preet" <prismati...@gmail.com>:

[Glenn Waldron]

Is that true? Setting an invalid bounding sphere will indeed suppress node-level culling, but I believe the near/far calculation is done at the Drawable level. See CullVisitor::apply(Geode&). 

The usual approach for terrain rendering is to subdivide your globe into tiles. Then OSG can cull out the tiles that are not in the view, including far-off tiles or back-facing tiles (by means of the ClusterCullingCallback). That will bring the far clip plane closer and give you the z-buffer resolution you need in order to visualize surface features. 

In addition, you can decrease the Camera's near/far ratio; this will give you a little more near clip space if you still need it.

Glenn Waldron / @glennwaldron

[Thrall, Bryan]

Preet wrote on 2012-10-04:
> Sorry if it wasn't clear; the items aren't being displayed because the
> near and far planes that osg sets creates a frustum that doesn't
include
> them. I need to manually set the near and far planes to see
everything.
>
> The near and far planes that osg sets without the earth surface
geometry
> is fine. Once you add the surface geometry though, the near and far
> planes are set such that the items are no long in the view frustum.

If the surface geometry is in view but the calculated frustum doesn't
contain it, then that sounds like a bug that should be investigated
further. Are you certain the frustum really doesn't contain the surface
geometry?

It seems more likely that the problem is with z buffer precision due to
the earth geometry pushing the far plane out so far that the surface
geometry is getting buried, as other people in the thread have
suggested.
--
Bryan Thrall
Principal Software Engineer
FlightSafety International
bryan....@flightsafety.com

[Tueller, Shayne R Civ USAF AFMC 519 SMXS/MXDEC]

We specify the near & far planes manually and we don't have z-buffer
issues with models on the earth's surface. Perhaps you should select the
option DO_NOT_COMPUTE_NEAR_FAR for cull settings...

-Shayne

[Sergey Polischuk]

Hi

 

I'm talking about setting this bounds callbacks on geometry(drawable) leaves.

 

05.10.2012, 17:20, "Glenn Waldron" <gwal...@gmail.com>:

,

[Glenn Waldron]

Indeed, my mistake.

Glenn Waldron / @glennwaldron

[Preet]

Sergey's suggestion (invalidating the geometry's bounds with a custom
compute bounds callback) sort of worked, but led into another issue.
If I zoom out far enough, the Earth surface geometry disappears.
Specifically, if the camera is pointing at the center of the Earth,
the Earth geometry disappears when the camera eye is further than
~5.13E6m from the surface of the Earth. Changing the near and far
planes don't have any effect here.

However, if I disable culling I don't have this problem (but disabling
culling kills the framerate):
myCam->setCullingMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);

So right now I'm:

* Setting the near and far plane manually
(myCam->setComputeNearFarMode is set to DO_NOT_COMPUTE) whenever the
camera is updated to ensure my desired view volume is correct
* Setting the Earth surface geometry compute bounds callback to disabled

And that works fine up until I move the camera out far enough as I
described previously. Something happens at that causes the geometry to
disappear unless I disable culling altogether.


Preet

[Preet]

On Sat, Oct 6, 2012 at 1:02 AM, Preet <prismati...@gmail.com> wrote:
> Sergey's suggestion (invalidating the geometry's bounds with a custom
> compute bounds callback) sort of worked, but led into another issue.
> If I zoom out far enough, the Earth surface geometry disappears.
> Specifically, if the camera is pointing at the center of the Earth,
> the Earth geometry disappears when the camera eye is further than
> ~5.13E6m from the surface of the Earth. Changing the near and far
> planes don't have any effect here.
>
> However, if I disable culling I don't have this problem (but disabling
> culling kills the framerate):
> myCam->setCullingMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);

Sorry, typo above, I meant to write:
myCam->setCullingMode(osg::CullSettings::NO_CULLING);

[Sergey Polischuk]

Hi

I believe this caused by small features culling (which is culling away objects which cover less space on screen than some pixel threshold). With compute near far enabled - when camera far enough objects on earth surface gets culled away, and as there are no objects on earth surface get's rendered, far plane calculated is just to close for earth to be visible.
To check if this causing problems try to set culling mode to myCam->setCullingMode(myCam->getCullingMode() & (~osg::CullSettings::SMALL_FEATURE_CULLING));

You can incorporate some logic into bounds computation to return valid bound when camera is far from earth surface, or disable small feature culling (or just reduce it's threshold)

Cheers.

06.10.2012, 09:16, "Preet" <prismati...@gmail.com>:

[Preet]

Hiya,

A combination of:

* setting the cull mode to
myCam->setCullingMode(osg::CullSettings::VIEW_FRUSTUM_SIDES_CULLING)
* manually specifying the near and far planes
* letting osg compute the right bounding box for the earth geometry by itself

seems to be working. Thanks to all for the help!