Hello Egon,  I load the 3D car model by jpct , I want to get the car width  height and length , int other way, how to get the car's boundingBox? How can I do this?  Thanks very much

You are greate !    set Y  = 0  it's OK !

Wow,  I perform an  lookat action, 　I get the SimpleVector from a curve , and   get this SimpleVector matrix , then set the car by this matrix ,

                        SimpleVector posAhead = way.PointOnPath(xp);   
         SimpleVector poscur = getTransformedCenter();
         posAhead.sub(poscur);
         rotMatrix=posAhead.getRotationMatrix();

                        //here    must set  X angle to 0
                        ? setXangle = 0
                        //
                        setRotationMatrix(rotMatrix);

Maybe this question is very simple,  but i  don't know how to do so , forgive me

I'm so sorry ,  the reason is I use the particle by a wrong way,  about 200 particles are visible in the world.  I change they are invisible , the framerate is Ok now (30fps) .   

Another question:  about the camera  follow the  player (car) , I use the code take from the car example,  when the car translate fast , the distance between camera and player  is becomes far ,  I want  the camera near the player , change the offset , but no effect , I don't know why?  How to ajust it by car speed ?  Thanks a lot !

final  float  Voffset = 8.6f;
final  float  Hoffset = 50f;

               Camera camera = world.getCamera();

          // Making this interpolation based on ticks fixes the jitter on low fps
           SimpleVector center=player.getTransformedCenter();
          
           SimpleVector oldCamPos=camera.getPosition();
           SimpleVector oldestCamPos=new SimpleVector(oldCamPos);
           oldCamPos.scalarMul(4f);

           SimpleVector camPos=new SimpleVector(center);
           SimpleVector zOffset=player.getZAxis();
           //SimpleVector yOffset=new SimpleVector(0, -18*zoomFactor*zoomFactor, 0);//50 (10)
          
           SimpleVector yOffset=new SimpleVector(0, -Voffset*zoomFactor, 0);
           //zOffset.scalarMul(-80f*zoomFactor*zoomFactor); //70
           /*if(player.speed != 0)
               zOffset.scalarMul(-30f*zoomFactor); //70
           else
              zOffset.scalarMul(-30f*zoomFactor);
           */
           //if(player.speed > 0)
           //   zOffset.scalarMul(-50f*zoomFactor /player.speed);
           //else
           /*
           if(player.speed == 0)
               zOffset.scalarMul(-Hoffset*zoomFactor);
           else
              zOffset.scalarMul(-Hoffset*player.maxSpeed/(player.speed) );
           */
           zOffset.scalarMul(-Hoffset*zoomFactor);
          
           camPos.add(zOffset);
           camPos.add(yOffset);

           camPos.add(oldCamPos);
           camPos.scalarMul(0.2f); //0.2f  1/(4+1)

           SimpleVector delta=camPos.calcSub(oldestCamPos);
           float len=delta.length();

           if (len!=0) {
              camera.moveCamera(delta.normalize(), len);
           }

           camera.lookAt(center);
 

Helloe Egon, I add 10 cars in my game , each car set  setCollisionMode(Object3D.COLLISION_CHECK_SELF|Object3D.COLLISION_CHECK_OTHERS);
and add  addCollisionListener(carCollision);    and called checkForCollisionSpherical  every frame,  I found the framerate droped huge , about 23 fps, normal  is 30fps , Could you help me to  improve the collision perfomace ?   very thanks 

Hello Egon,  I  get some .ser file  and I want to convert them to obj file , but I don't know how to do this , can you help me ? Thanks very much !