start_layer = thisComp.layer("Start Null");
end_layer = thisComp.layer("End Null");
pos_start = start_layer.transform.position;
pos_end = end_layer.transform.position;
index_start = start_layer.index;
index_end = end_layer.index;
layer_count = index_end - index_start;
this_layer_pos = pos_start + (pos_end-pos_start)/layer_count*(index-index_start)