[osg-users] Finding the edge of a frustum, or intersection with the edge of a frustum

[Brad Colbert]

Hi,

I'm using an ortho frustum to draw a map.  On the map I'm drawing a kind of range ring / sector pattern, starting from an origin using lines.  I want to draw text at the edge of the viewport where the lines intersect with the edge (well, just inside so the text is viewable).

The problem I'm having is I can't quite figure out how to tell where the lines end within the frustum.  Any ideas would be welcomed.

Picture for context is attached.

Thank you!

Cheers,
Brad

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Attachments: 
http://forum.openscenegraph.org//files/mapview_458.png