[osg-users] LineSegmentIntersector

[OpenSceneGraph Users]

Hi Andrew,

When you say you have a isometric view, to be clear, you mean you have an
orthographic projection of the scene?  The OSG itself support orthographic
projection via the osg::Camera's ProjectionMatrix, the intersection.  It
can only account for this if the IntersectionVisitor knows about it's
setting.

Have you tried the osgViewer::View(er)::computeIntersections(..) method?

This method knows about the View's Camera so can account for it's
projection matrix.

Robert.

On Tue, 14 Apr 2020 at 23:35, OpenSceneGraph Users <
osg-users at lists.openscenegraph.org> wrote:

> Hi,
> I am having a lot of problems with picking with LineSegmentIntersector in
> OSG 3.6.5.
>
> I have reduced the problem to a a simple cube, center 0.5,0.5,0.5 with a
> boundingSphere radius of 1.2142
>
> I create the intersection with ( x , y are screen coordinates)
>
> picker=new osgUtil::LineSegmentIntersector ( osgUtil::Intersector::WINDOW,
> x, y );
> osgUtil::IntersectionVisitor iv ( picker );
> getCamera()->accept ( iv );
>
>
>
> When I am "close" to the model geometry in an isometric view ( the cube
> fills,say, 50% of the screen), this works perfectly. I get the exact
> intersections coordinates I expect.
>
> When I "pull the camera back" from the geometry and the object is much
> smaller on the screen, the intersections fail.
>
> After much debugging, the problem is that the intersector fails the test
> of the intersection of the line with the bounding sphere of my model
> geometry
>
> Specifically I send up in
>
> bool LineSegmentIntersector::intersects(const osg::BoundingSphere& bs)
>
>
> The BoundingSphere is in "model space" , and correct, but the _start and
> _end points used in the calculation are incorrect to intersect the sphere
> in model space and so the intersection fails.
>
> _start {_v=0x000001ba7308d300 {13.227287349450325, -2.9785854231569449, -
> 5.5167534692525066} }
> _end {_v=0x000001ba7308d318 {11.072576448741074, -5.1332963238661939, -
> 7.6714332827528793} }
>
> Any ideas what is going on. It seems although the vector of start and end
> is the correct vector ( or the "closer" picking would not work), something
> is wrong in the transformation into model space.
>
> Thx
> Andrew
>
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