[osg-users] Using OsgSim Overlay

[Vaibhav Bansal]

Hello,

I have added a geometry as an overlay over another geometry.
The overlay texture seems to distort(stretch) under certain viewing angles.
It seems the projected texture is generating incorrect texture coordinates.

The white area is the overlaySubgraph geometry, and the colored area is the
Overlay Node (base) geometry.
The overlay mode is VIEW_DEPENDENT_WITH_ORTHOGRAPHIC_PROJECTION.

Can anyone suggest where should I start troubleshooting.

Thanks
Vaibhav Bansal

[J.P. Delport]

Hi Vaibhav,

Vaibhav Bansal wrote:
> Hello,
>
> I have added a geometry as an overlay over another geometry.
> The overlay texture seems to distort(stretch) under certain viewing angles.
> It seems the projected texture is generating incorrect texture coordinates.

The texture coordinates might be OK, but the resolution of your
overlayed geometry might change in the generated overlayed texture. What
happens in OBJECT_DEPENDENT_WITH_ORTHOGRAPHIC_OVERLAY? Does the
resolution/stretch stay the same?

jp

>
> The white area is the overlaySubgraph geometry, and the colored area is the
> Overlay Node (base) geometry.
> The overlay mode is VIEW_DEPENDENT_WITH_ORTHOGRAPHIC_PROJECTION.
>
> Can anyone suggest where should I start troubleshooting.
>
> Thanks
> Vaibhav Bansal
>
>

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[Vaibhav Bansal]

Hello jp,

Thanks for the quick reply.
How do I check if the 'resolution' of ovelay geometry is changing.

Regards
Vaibhav Bansal

[J.P. Delport]

Hi,

Vaibhav Bansal wrote:
> Hello jp,
>
> Thanks for the quick reply.
> How do I check if the 'resolution' of ovelay geometry is changing.

imagine the following:
You want to overlay a 1024x1024 checkerboard onto the earth and you have
a 512x512 overlay texture. If you view the whole earth it obviously
would not look good - too much detail to fit into the texture. What the
view dependent modes try to do is this: When you zoom in, you only see a
piece of the checkerboard, so now the 512x512 texture can contain only a
piece of the checkerboard and so you see "more detail" of the overlayed
geometry.

I think this is the effect you are seeing when you are moving the view
around.

jp

[Vaibhav Bansal]

Yes, this is what the overlay node does for me.
But I am unable to understand, why the stretching occurs only 'at' some
specific angles.

[Glenn Waldron]

Vaibhav,

The area covered by the projected texture changes based on your view angle. As your angle of view gets less steep, the texture resolution appears to descrease since it has to cover a larger area. Try view-dependend-with-perspective-overlay, which helps with this issue. Also, increase the texture size hint in the OverlayNode api.


Glenn Waldron : Pelican Mapping : http://pelicanmapping.com : +1.703.652.4791

[J.P. Delport]

Hi,

Vaibhav Bansal wrote:
> Yes, this is what the overlay node does for me.
> But I am unable to understand, why the stretching occurs only 'at' some
> specific angles.

Are the transitions smooth or are you seeing jumps?

[Vaibhav Bansal]

Hello Glenn,

 

The view dependent-with-perspective-overlay uses a shader, I am already using a shader for my terrain(base geometry, osgearth).

Secondly for VIEW_DEPENDENT_WITH_ORTHOGRAPHIC mode the projected texture resolution does not decrease(/projected area does not increase) even when the viewing direction is near parallel to terrain, it stretches ‘only’ at certain specific angles.

 

Is there a way to use overlay if I am already using a shader on my base terrain?

 

Thanks and Regards

Vaibhav Bansal

[Glenn Waldron]

I'm no shader expert, so I cannot answer that.

I do know that osgEarth plays well with OverlayNode though -- it has some built-in vector overlay support that uses OverlayNode in perspective mode (see the osgearth_feature_overlay driver).

Glenn Waldron : Pelican Mapping : http://pelicanmapping.com : +1.703.652.4791

[Vaibhav Bansal]

Smooth, I would say distortions occur in certain angle ranges.

[Vaibhav Bansal]

Hello Glenn,

 

Thanks for your help.

 

I was working on osgearth1.2 till now, however on your advice I updated to latest svn.

I ran shapefile_overlay.earth provided with osgearth tests on osgviewer.

However it seems that the artifacts were still reproducible L at certain viewing angles.

(It was not there just for a fration for texture update but persisted at that viewing angle)

 

Attached ScreenShots.

 

It seems that I will have to look into the code of overlay node.

[Glenn Waldron]

Vaibhav,

You may also want to investigate the shapefile_stencil.earth example (which uses the model_feature_stencil plugin). This uses a stencil buffer technique to drape vector data on the terrain. Make sure you get the absolute latest SVN though. For lines, you'll need to build in the GEOS support as well (use geos 3.1.1 on windows) to get geometry buffering.

Glenn Waldron : Pelican Mapping : http://pelicanmapping.com : +1.703.652.4791

[Vaibhav Bansal]

Thanks Glenn for the tip J

 

Best Regards