CALIBRATION OF THE SR4500 TIME-OF-FLIGHT CAMERA FOR OUTDOOR MOBILE SURVEYING APPLICATIONS: A CASE STUDY

Abstract

3D-cameras based on Time-of-Flight (ToF) technology have recently raised up to a commercial level of development. In this contribution, we investigate the outdoor calibration and measurement capabilities of the SR4500 ToF camera. The proposed calibration method combines up-to-date techniques with robust estimation. First, intrinsic camera parameters are estimated, which allows converting radial distances into orthogonal ones. The latter are then calibrated using successive acquisitions of a plane at different camera positions, measured by tacheometric techniques. This distance calibration step estimates two coefficient matrices for each pixel, using linear regression. Experimental assessments carried out with a 3D laser-cloud after converting all the data in a common basis show that the obtained precision is twice better than with the constructor default calibration, with a full-frame accuracy of about 4 cm. Moreover, estimating the internal calibration in sunny and warm outdoor conditions yields almost the same coefficients as indoors. Finally, a test shows the feasibility of dynamic outdoor acquisitions and measurements.