In the datasheet and promotional materials of common 3D depth cameras on the market, we often see two terms: accuracy and precision, expressed as “high-accuracy” or “high-precision”. On dictionary, the two terms are defined mutually, so they are easily mistaken to be the same thing. Actually, in the fields of science, engineering, and statistics, they refer to different things.
Both accuracy and precision are used in the field of measurement. Accuracy is the closeness of a measured value to a true value, while precision is the closeness of a measured value to other measured values. A good example is the measurement of a shot on target. The measurement of the results is dependent on the closeness of the shots to the bull’s eye, namely, the center of the target. As shown in the pictures below, (a) represents both high accuracy and high precision, because the shots are close to the center and each other. (b) shows high-precision but low-accuracy results as the shots are close to each other but far from the center and (c) displays the opposite. (d) shows the worst results, where both accuracy and precision are far from the center. Therefore, a measurement can be both accurate and precise, or neither, or accurate but not precise, or precise but not accurate.
It should be noted that repeatability, a concept relevant to precision, is also frequently used, particularly in descriptions of industrial-grade mechanical products. It refers to the closeness among successive measurements carried out with the same method by the same operator under identical conditions.
In 3D depth sensing, accuracy and precision are often measured at submillimeter level, used to represent the quality and stability of 3D outputs. For example, Revopoint’s Acusense 3D depth camera achieves an average accuracy of 0.5mm, and at a closer range within 0.2 meters, the accuracy can reach even higher, up to 0.1mm, better than the Realsense D400 series 3D depth cameras. For industrial-grade 3D depth camera, which strictly requires higher level of accuracy, precision or repeatability becomes a highlighted parameter, since it signifies the stability and reliability of the camera. The 3D depth camera Rayscan from Revopoint, has a depth repeatability ranging from 5μm to 50μm, enabling it to inspect intricate workpieces.