Accuracy Testing of 3D Scanners - The Dot Finding Method

There is a simple way to test a 3D scanner's accuracy that many companies have the resources to perform:

Step 1: Place a series of photogrammetry dots on a 3D-shaped object, such as a table with several blocks on it, or a chair seat, legs, and floor. The goal is to fill the 3D scanner's calibration field of view, and also fill the Z depth of the system's calibration.
Step 2: Perform a photogrammetry session on the dots using a standard photogrammetry system (this can often be performed as a service if your company doesn't have a photogrammetry system)
Step 3: Measure the targets with the 3D scanner. Most high-end/industrial 3D scanners have dotfinders. Collect only a single shot of the targets.
Step 4: Export the targets measured by the 3D scanner.
Step 5: Compare the targets measured by the 3D scanner with the same targets measured by the photogrammetry session.


WHY IS THIS A GOOD TEST? Because targets are one of the easiest things to measure in the optics world. It is a well-understood process to find white dots on a black background in the imaging processing world. The accuracy of the measured dot will almost ALWAYS be more accurate than the accuracy of the 3D scanner's surface measurement capabilities, because projected patterns will not be found as accurately as targets.

Targets represent perfect contrast on a perfectly white, Lambertian (diffuse) surface against a perfectly black, Lambertian (diffuse) surface, on a perfectly-round circle. Fringes and projected patterns, on the other hand, are much more difficult to locate in the camera image. Since the 3D reconstruction (either targets or surface) is intimately linked to how well the features are found in the camera image, the "Dot Finding Method" provides a clear window into the system's calibration.

If you would like assistance conducting a metrology study such as this, we would be happy to assist!