Scenekit - Ploting the trajectory of an object - animation

Question

Ok, I was not very sure about the earlier conversion formula as someone pointed out (I just read it somewhere and tried out), but now I am trying out an approach where I have a tiny Box created at the edge of the ship and I keep on reading its positions as rotation is applied to the ship..then using these positions to plot the geometry..Below is the relevant code:
scene = [SCNScene sceneNamed:#"ship.scn"];
_viewpoint1.scene = scene;
box = [SCNNode node];
box.geometry = [SCNBox boxWithWidth:.1 height:.1 length:.1 chamferRadius:.1];
box.physicsBody = [SCNPhysicsBody staticBody];
// position the box to the end of the ship
box.position = SCNVector3Make(box.position.x, box.position.y, box.position.z +5.6);
[_viewpoint1.scene.rootNode addChildNode:box];
As the app receives quaternions, the ship rotates and so does the box at the tip, and I capture the positions of that box and store it in positions array.
_viewpoint1.scene.rootNode.orientation = SCNVector4Make(f_q0, f_q1, f_q2, f_q3);
SCNVector3 pt = [box convertPosition:SCNVector3Make(box.position.x, box.position.y, box.position.z) toNode:nil];
[positions addObject:[NSValue valueWithSCNVector3:SCNVector3Make(pt.x, pt.y, pt.z)]];
Later, using this positions array to create the geometry as below:
SCNVector3 positions2[pointCount];
for (int j = 0; j < pointCount; j++)
{
SCNVector3 value = [[positions objectAtIndex:j] SCNVector3Value];
SCNVector3 value1 = [_viewpoint2.scene.rootNode convertPosition:value fromNode:nil];
positions2[j] = value1;
};
SCNGeometrySource *vertexSource1 =
[SCNGeometrySource geometrySourceWithVertices:positions2 count:pointCount];
NSData *indexData1 = [NSData dataWithBytes:indices2
length:sizeof(indices2)];
SCNGeometryElement *element1 =
[SCNGeometryElement geometryElementWithData:indexData1
primitiveType:SCNGeometryPrimitiveTypeLine
primitiveCount:pointCount
bytesPerIndex:sizeof(int)];
SCNGeometry *geometry1 = [SCNGeometry geometryWithSources:#[vertexSource1]
elements:#[element1]];
SCNNode* lineNode1 = [SCNNode nodeWithGeometry:geometry1];
[_viewpoint2.scene.rootNode addChildNode:lineNode1];
What I observe is that the arc drawn is bigger than the ship rotation, so if the ship rotates by 30 deg, the arc drawn is about 60 deg or so..it should be the same as the ship rotation...wondering what I am doing incorrect here?