I have classified the cloud points of LiDAR data into different classes. After extracting I have generated 3d building polygons using "Vectorize buildings" option from terrascan tools. Now I need to extract the outer lines of those entire 3d buildings in polylines. Extension of output file is .dgn only. Yellow coloured lines in the illustration are polylines. I drew them manually. I need to extract the rooftops including chimneys and other things above the roof. Is there any method to extract them automatically?