Wall shadow removal problems differ due to configuration of walls in different propagation scenarios. Applying Weiler-Atherton polygon clipping method helps calculate illuminated regions on the building walls, but unfortunately the technique has limitation when there are many walls and the walls configuration is complex. The modified Weiler-Atherton polygon clipping method proposed can solve the problem by regarding all vertices of the subject polygon or clipping polygon, that are also intersection points as simply intersection points. In the case that a certain vertex of the subject polygon is a vertex of the clipping polygon, this vertex of the subject polygon is still considered a vertex. It is found that wall shadow removal using the proposed modified Weiler-Atherton polygon clipping method is more efficient.