How Do I Position a Laser Scanner to Scan a Façade?
Correctly positioning a laser scanner is an essential prerequisite for obtaining a complete and meaningful point cloud. In the series “True Laser Scanning” we make notes on the fundamental points for excellent scanner use. In this article we cover choosing the optimal laser scanner positions when scanning oversized facades.
A laser scanner can detect only that which is visible from the scanner center. We advise our customers to “Look through the eyes of the scanner”; all you can see with your eyes is identical to what is detected by your laser scanner and shown later in the point cloud. You will quickly find that you cannot look behind objects or around corners ;).
Accordingly, it is always advisable to view your intended target from different laser scanner locations; for complex, high-detail facades it is always better to scan too much rather than too little.
Avoid horizontal shading
Consider a wall in plan view. In the example shown, you can see quickly (see green circle) that left rear corner and the left window reveal is not detected by the laser scanner. Accordingly, a further laser scanner location is required for the detection of the left jamb.
In the following picture you can see how the shaded areas are detected by the second (blue) scanning position. A large part of the facade will be detected with the second scan position, and combining the two will give you a higher density of the point cloud and thus better detailing.
Also consider vertical shadows in the laser scanner sighting
Issues of vertical shading also occur in the scanning process. Imagine the following scenario.
Using a scanner with a low elevation will throw a “shadow” onto the lower half of the window. In order to obtain a full detailed scan of the window, raise the scanner on a tripod or elevated platform until it is roughly the same height as the center of the window; this will ensure an accurate point cloud rendering.
Please take notice of our article: True Laser Scanning – Part 02 Correct Laser Scanner Resolution