[osg-users] LineSegmentIntersector

[OpenSceneGraph Users]

In my case its Perspective.


I was able to work around the problem by using a PolyTope intersector with 
a 1x1 rectangle. That worked perfectly.

On Tuesday, April 14, 2020 at 11:56:24 PM UTC-7, OpenSceneGraph Users wrote:
>
> 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-... at lists.openscenegraph.org <javascript:>> 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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