It's really simply to solve. Don't use any dummy objects and stuff, just rotateY around the origin and all is fine:
groundModel.setRotationPivot(SimpleVector.ORIGIN);
moveTo(groundModel, SimpleVector.ORIGIN);
keepGoing = true;
while (keepGoing) {
draw();
groundModel.rotateY(-.02f);
try {
Thread.sleep(10);
} catch (InterruptedException e) {
System.err.println("Trouble sleeping: " + e.getMessage());
}
}
However, using this model, it doesn't look 100% right if you are taking the seats as a reference (it does look right if you use that structure in the center though), simply because the seats are not correctly aligned with center structure. While the center is point symmetric, the seats are not. So even if everything is setup correctly, the seats move on some ellipsoid path simply because they form an ellipsoid and not circle.