3-D 3D reconstruction 3D urban expansion 5G signal simulation DTM extraction GIS data Gabor filter Inria aerial image labeling dataset LiDAR LiDAR point cloud Massachusetts buildings dataset T1-995 TA1-2040 TH1-9745 U-Net VHR remote sensing imagery accuracy analysis active contour model aerial images attention mechanism binary decision network boundary extraction boundary regulated network building building boundary extraction building detection building edges detection building extraction building index building reconstruction