LiDAR (Light Detection and Ranging) technology can be used to measure an existing building by emitting laser beams and measuring the time it takes for the beams to bounce back. This information can be used to create a 3D model of the building, including its size, shape, and topography. LiDAR can also be used to detect changes in the building over time, such as structural damage or wear and tear. Additionally, LiDAR can be used to accurately measure the height of buildings, which can be useful for construction, surveying, and architectural purposes.