Register point clouds using laser scanning reference spheres
In this user story, we want to find out the distance between scanner and reference spheres allowing spheres to be registered still well in FARO Scene software. Simply put: At what distance may I position my targets so that I can use them for scan registration.
We have prepared a test area of 35m length. The FARO Focus 3D laser scanner was set at 0.00m. Starting at 7.5m, reference spheres were positioned every 2.5m. About the reference spheres: The following spheres of our product range were tested: Flexi, Basic, Traveler, UltraX (diameter 0.145m each time) and XXL (diameter 0.2m). The analysis was reduced to both standard types of spheres (0.145m and 0.2m diameter).
The analysis of Flexi, Basic, Traveler and UltraX didn't reveal any significant differences. The charts below show distances/resolutions/qualities a successful registration can be expected for. (Indications for resolution and quality result from the selection options in FARO Focus 3D scanner; thus, they cannot be assigned to other scanners.)
In our measurements, all four spheres showed jus minor deviations. At a distance of up to 20m, spheres can perfectly be registered automatically (green). In the yellow section, automatic registration can still be realized but you should realize that less than 80 scan points were used for calculating the matching. You should decide situation-dependently if you want to use the reference sphere for registration or not. In the red section, teh algorithm for automatic target detection fails since too less scan points exist.
In close range, the reference sphere Basic convinces in almost all scanner settings (resolution and quality) and can be registered automatically at more than 30 meters when defaultstandard settings are chosen.
Concerning detection properties, the reference sphere Flexi is on the same level as reference sphere Basic. However, Flexi is significantly more sturdy and thus more durable than Basic.
The reference sphere UltraX is the most precise one of all three standard spheres. Most scan points for calculation matching are detected on the UltraX sphere.
The reference sphere Traveler is automatically detected in many scanner settings within up to 20 meters. The laser scanner sphere Traveler is characterized by the small pack size that is attractive especially for frequent travellers.
The laser scanner reference sphere XXL was designed particularly for large distances. That's why we didn't test a detection in less than 15 meters.