Explain LiDAR technology and its applications in civil engineering.

LiDAR (Light Detection and Ranging) uses laser pulses to measure distances to objects, generating dense 3D point clouds. Airborne LiDAR from aircraft or drones covers large areas rapidly. Ground-based/terrestrial LiDAR provides detailed scanning of structures and sites. Multiple returns capture vegetation and ground surface. Data processing: filtering, classification (ground, buildings, vegetation), and surface generation. Applications: topographic mapping, corridor surveys for roads/transmission lines, flood modeling, building documentation, volume calculation, and as-built verification. Achieves vertical accuracy of 5-15cm for airborne, millimeter-level for terrestrial.