[osg-users] Getting world coord bounding box

[Siddharth Palaniappan]

Hi daniel,

I read thru this at the osg site :

http://www.openscenegraph.org/projects/osg/wiki/Support/Maths/MatrixTransformations

In the end , robert says ways are defined ... i initially multiplied the matrix on the left side. But after reading this i changed it...am i wrong ?

Siddharth

----- Original Message ----
From: Daniel Holz <danielh at cm-labs.com>
To: OpenSceneGraph Users <osg-users at lists.openscenegraph.org>
Sent: Saturday, December 1, 2007 2:35:52 PM
Subject: Re: [osg-users] Getting world coord bounding box


hi,

don't you have to multiply the matrix from the left side with the 
vector, like this:
M * x = x',
whereas M is your 'WorldCoordsMatrix', x is your local BBox vector and 
x' is the same in world coords.

hope this helps.

daniel

Siddharth Palaniappan wrote:
> Hi osg users,
>
> I'm currently using openscenegraph for my class project to simulate
 traffic. I have a problem in that , i need to find collision detection
 between consecutive cars and stop the car if  there is a collision.  I
 have followed the osgExample- for animation. I have used an
 animationpath and animationpathcallback and i have implemented my own spline
 interpolation for the car to traverse on a spline. I tried to get the world
 coordinate of the bounding box like this..
>
> * i have a class Vehicle that stores the node to which an openflight
 model is read into.
>
> * the leaf node is the node having the vehicle, the parent node of
 this node is a transformation node which has an animationpathcallback set
 to, and this also has a parent node to initially set the location and
 orientation, (just like in the osgExample animation).
>
> * i have a node visitor that traverses parents..so it goes from the
 current node to the root concatenating all the world coordinates.
>
> * then i get the local bounding box of the node and get the minimum
 and maximum and multiply the world coord matrix with these points to
 form a new min and max point and create a new bounding box. I do this for
 every two node to check the intersection of two consecutive nodes. 
>
>
>     //getWorldCoords() - forwards to a nodevisitor to get world
 coords matrix.
>     osg::Matrixd* WorldCoordsMatrix = getWorldCoords(this->m_Vehicle)
 ;
>     osg::BoundingBox VehicleBBox ;
>
>     VehicleBBox.expandBy(m_Vehicle->getBound()) ;
>
>     //Convert the vehicle local coords to world coordinates.
>     osg::Vec3f MinPt(VehicleBBox.xMin() , VehicleBBox.yMin() ,
 VehicleBBox.zMin()) ;
>     osg::Vec3f MaxPt(VehicleBBox.xMax() , VehicleBBox.yMax() ,
 VehicleBBox.zMax()) ;
>
>     osg::Vec3f NewMinPt , NewMaxPt ;
>     NewMinPt = MinPt * (*WorldCoordsMatrix) ;
>     NewMaxPt = MaxPt * (*WorldCoordsMatrix) ;
>
>     this->m_VehicleBoundingBox = new osg::BoundingBox(NewMinPt ,
 NewMaxPt) ;
>
> I am not getting correct results. I get that the bounding boxes dont
 intersect at all or sometimes intersect at odd places. Please let me
 know if i'm doing something stupid or if i my understanding of anything
 wrong. 
>
>
> Thank you,
>
> Yours Sincerely,
>
> Siddharth
>
>
>
>
>
>
>      
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