Thank you very much, exactly what I needed.
Code for those who need it:
private boolean isPointOnScreen(Entity e) {
if (e != null) {
ArrayList<Polygon> poly = GraphicUtilities.getModelMeshTriangles(bot, e.getGridX(), e.getGridY(), e.getZ(),
e.getModel());
for (Polygon p : poly) {
if (GraphicUtilities.MAIN_SCREEN_CLIP.contains(p.getBounds())) {
return true;
}
}
}
return false;
}