If you use a combined matrix as rotation matrix, you'll change the rotation pivot by this translation. The new rotation pivot should be the negative translation.

If I set the negative pivot as pivot, the model will instantly snap back to its previous position when trying to rotate it.

I've tried the other solution, but since it uses a different (geographic) coordinate system again, it doesn't work either. The model gets attached to the camera and doesn't stay where it should.

I was asking the thread author

Usually, onCreate is only called if the activity is, well, created. If you switch to another activity, the current one is paused. If you switch back to the paused activity onResume() is called. But since on switching activites the OpenGL context may get destoyed and you need to re-initialize your 3D-stuff. Depending on where you do that, onResume() or onSurfaceChanged() is a good place to do so.

Just that I get it right:
What should I use for VIEWPLANE_Z_VALUE, the far clipping plane?

//...
public SimpleVector reproject2D3DWS(Camera camera, FrameBuffer buffer, int x, int y, SimpleVector toFill) {
SimpleVector ray = Interact2D.reproject2D3D(camera, buffer, x, y, 2000, toFill);
ray.matMul(camera.getBack().invert());
return ray;
}

public void findNearestObject(int touchX, int touchY) {

SimpleVector dir = reproject2D3DWS(camera, frameBuffer, touchX, touchY, new SimpleVector()).normalize();
Object[] res = world.calcMinDistanceAndObject3D(camera.getPosition(), dir, 10000);
              //...
}


Is that correct?

Thanks, that brought me on the right track. The AR-engine converted the pose to a OpenGL-compatible matrix beforehand, which additionally screwed my calculations. But now I have some trouble doing the correct conversions between the coordinate systems now.
The AR-engine uses a right handed system (Picture). According to your wiki, I need to rotate the matrix by 180° around x to convert it to the jPCT system. But do I need to do it before or after setting the camera matrix? I currently extract the rotation/translation from the float array, dump it into a Matrix/SimpleVector, rotate the Matrix/SimpleVector by 180° around x and set them as the backbuffer/position. The car is fixed to the marker, but behaves totally unpredictable (it seems as the model sticks to the camera, and not to the marker) as I move around my device, so I guess my conversion is wrong.

I thought I share my simple implementation of the serializer (for *.obj and *.mtl files) for the Android version, might be useful for others. If you don't mind, you can add it to the wiki.
I expected worse when I read that "It's a bit painful to use right now"  It has no special error checking etc., but its usable and should be quickly adaptable for other filetypes.

import java.io.FileOutputStream;
import com.threed.jpct.DeSerializer;
import com.threed.jpct.Loader;
import com.threed.jpct.Object3D;

public class Serializer {

              //Adjust the paths as necessary
private static final String INPUT_MODEL = "c:/myobj.obj";
private static final String INPUT_MATERIAL = "c:/mymtl.mtl";
private static final String OUTPUT_FILE = "c:/serialized.obj";

public static void main(String[] args) {

Object3D[] objs = null;
objs = Loader.loadOBJ(INPUT_MODEL, INPUT_MATERIAL, 1);

for (Object3D o : objs)
o.build();

DeSerializer ds = new DeSerializer();

try {

FileOutputStream baos = new FileOutputStream(OUTPUT_FILE);
ds.serializeArray(objs, baos, true);

} catch (Exception e) {

e.printStackTrace();
}

}

}

Load in jpct-ae with:

/...
Object3D[] serializedObject = null;
serializedObject = Loader.loadSerializedObjectArray(res.openRawResource(R.raw.INSERT_FILE_NAME));
/...


I thought that I could somehow get access the sub-objects that the compiler mentioned (i.e. check if a collision occured with such a sub-object).

Edit: I think they are called groups inside the *.obj file.

Edit2: I obviously completely failed to realize, that all of those sub-objects are loaded independendtly. I just mashed them together with mergeAll() and overlooked that you can shove all sub-objects from the Obj-Loader into an Object3D[]-Array. 

Hi.

I'm loading a Wavefront obj file, that consists of serveral sub-objects (I noticed that jpct processes each of these objects when compiling). Using the picking tutorial from the wiki, I can now successfully choose between the objects I have in my scene with the touchscreen. It would now be interesting to somehow access (like adding transparency, or removing them temporarily) these sub-objects. I found that I can create a PolygonManager from the object, but it doesn't seem to help me, because I can only manipulate the polygons (duh). Is there any way to get access to the sub-objects in jpct?