Ways to verify performance of 3D imaging instruments

Abstract

Currently work is underway to establish standards for the performance verification of 3D imaging instruments including scanners, imagers, and flash LIDAR devices. This paper discusses the figures of merit to be considered in evaluating alternative methods, and it proposes specific ranging test protocols. Experimental results are reviewed. KEYWORD LISTscanner calibration, 3D measurement, 3D imaging, E57, ranging protocol, laser tracker, laser scanner I TRODUCTIOThree-dimensional (3D) imaging instruments measure the shape and size of objects or environments in three dimensions. These instruments are increasingly important in a wide range of applications, which depends partly on the maximum range of the particular imaging instrument. Short-range 3D imaging instruments have a maximum measurement range of up to a few meters. Many of these short-range devices measure 3D position using triangulation, although other methods are used.Mid-range imaging instruments measure up to a few hundred meters, and long-range imaging instruments measure up to many kilometers. One type of imaging instrument, which may be mid-or long-range, is flash LIDAR. This type of device is similar to a digital camera except that, besides providing angular irradiance information to each pixel, it also provides each pixel with a distance value.The main type of 3D imaging system considered in this paper is the spherically based laser scanner. This type of device, which may be mid-range or long-range, emits laser light from the origin of a spherical coordinate system and projects it onto an object of interest. The light scattered by the object is picked up by an optical detection system within the instrument. The light is converted into an electrical signal that is analyzed to find the distance to the target. Angle measuring means such as angular encoders are used to measure the angle of emission of the laser beam. From the combination of angle and distance information provided by the scanner, the 3D coordinates of objects in space can be found.Currently there are no widely accepted standards for procedures to verify the performance of 3D imaging systems. The committee E57 has been formed within ASTM to develop standards for 3D imaging systems. As a first step in the development of comprehensive standards, the committee is working on the development of a ranging protocol. The ranging protocol is a test method for checking the ranging performance of a 3D imaging instrument against a manufacturer's specification. The term "ranging" in here indicates that the instrument is checked along a preferred direction, which in the case of a spherically based laser scanner is outward from the instrument origin. Ordinarily the origin of the spherically based laser scanner is the instrument gimbal point.

Performance evaluation of terrestrial laser scanners—a review

“…The group focused on test methods for ranging errors, as the ranging unit is a critical component of TLS systems and its standardization was a task that they believed was manageable in a reasonable time frame. Early progress in ranging error evaluation by committee members in this group is described in [82,[107][108][109].…”

“…Bridges [109] proposed a method that involves using a laser tracker as the reference instrument with stands placed at the desired locations, all nominally collinear with the laser tracker. Each stand holds a kinematic seat that can accommodate either the T-bracket shown in figure 15 or a flat-plate target for the TLS.…”

Performance Evaluation of Triangulation Based Range Sensors

“…In the 3D imaging domain, the definition of best practices that led to standards started less than 15 years ago [ 4 ]. Measurement accuracy and uncertainty related to the various 3D imaging systems have been reported for specific applications in a metrological laboratory with controlled conditions [ 5 ], or for practical usage in less controlled conditions, with emphasis on triangulation based range devices [ 6 ]. For Time of Flight (TOF) based devices, a specific set of tests has been reported by Bohler et al regarding both accuracy and resolution in standard conditions [ 8 ], and by Guidi et al for their use at low scanner-to-target distance [ 9 ].…”

Proposed NRC portable target case for short-range triangulation-based 3D imaging systems characterization

“…There are three positions along the longest axis of the measuring volume at three different standoff distances defined as the minimum (1), median (2) and maximum (3) distance. Another position is on the axis perpendicular to the first axis at a median standoff distance (4). The plate must also be orientated on two of the body diagonals of the measuring volume (5 and 6).…”