Case study

Testing of laser scanning checkerboard targets - A comparison of targets

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Vergleichstest: Erkennung von Laserscanner-Zielmarken in Abhängigkeit von der Entfernung

Im Rahmen eines Vergleichs haben wir zwei der in unserem Laserscanning Europe Zielmarken Sortiment befindlichen Targets für Sie getestet. Untersucht wurden die beiden Black & White-Targets in den Ausführungen: Kleine Laserscanner-Zielmarkentafel (24 x 21 cm) und Große Laserscanner-Zielmarkentafel (45 x 42 cm). Ziel war es, herauszufinden wie sich die Erkennung der Zielmarken mit zunehmender Entfernung zum Scanner verhält. Die Auswertung erfolgte mit der Software Faro Scene, im Modus der automatischen Zielmarkenerkennung. Dabei wird in der Software einfach auf die Zielmarke (Target) geklickt und ein Algorithmus sucht nach dem Stoßpunkt der beiden schwarzen Rechtecke.

In the scope of a comparison, we have tested two checkerboard targets from our range of targets marks. We have compared two black & white checkerboard targets in the following versions: small checkerboard (24cm x 21cm) and large checkerboard (45cm x 42cm). The objective was to make out how the detection of targets behaves with increasing distance to the scanner. The analysis was made with FARO Scene software in the mode automatic target detection. That means we simply click on the target and an algorithm searches the intersection point of both black rectangles.

Test set-up

For testing the large checkerboard targets, we have chose the following set-up:

The following measurement setup was selected for testing the small checkerboard targets:

Analysis & results

Detection of large targets by use of automatic target detection works great at a distance of 12.5 meters and with 1/8 resolution. There are no results for distances of 7.5 and 10 meters available - This depends on the size of the large target. Since the "large" target is significantly larger than the "small" one, more scanning points can be found on the large target. Thus, software can detect the large checkerboards even at higher distances and average resolutions (1/5 at 35m) without any problems. It can be supposed that the large targets are visible even at distances of about 50 meters. This way, point clouds can be merged even at medium-sized distances.

The detection of small targets by means of automatic target detection works very great at a distance of 7.5 meters. Detection works for almost all selected resolutions. Only at 1/32 resolution, 7.5m distance provide too few points to determine the target's center. As might be expected, the visibility decreases with increasing distance. At a distance of 35 meters, the small target can easily be detected at 1/2 resolution.

 

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