A technique for improving webcam precision in biological plant measurement

In an attempt to harness webcam technology for the biological monitoring of grassland plants, a Microsoft LifeCam-based photogrammetric system was developed for the remote capture of 3D measurements of plants. Research was necessary to determine the metric quality of this webcam imagery for photogrammetric 3D measurement. This paper presents the details of a qualitative evaluation of a LifeCam VX-3000 for indoor and outdoor photogrammetric measurement together with the results of a case study involving two common small grassland plants. In the evaluation, laboratory and in-situ principal distance (PD) determination techniques were performed, thus evaluating the significance of the latter for improving measurement accuracy in an uncontrolled environment despite the ineffective focusing of this imaging sensor. The effect of outdoor ambient temperature on the PD was investigated. Results show that sharp focusing is a problem with this webcam, as shown by the disparity of the laboratory-determined PD of various object distances. However, the determination of the PD using field images improves the measurement accuracy. Using this approach, 3D measurement accuracy of between 0Æ3±0Æ2 and 1Æ7±0Æ4mm was achieved, depending on the type of grass observed and the digitising technique used