Calculating the effect of dual-axis scanner rotations and surface orientation on scan profiles

The large volumes of point cloud data collected by a Mobile Mapping System(MMS) equipped with a laser scanner have attracted the attention of the research community, primarily towards developing automated algorithms to help when processing this data. This has resulted in insufficient attention being paid to quantifying the capabilities of these systems, and due to the relative youth of this technology there is no concrete understanding of the point density that different hardware configurations and operating parameters will exhibit on objects at specific distances. Obtaining the required point density for a project impacts on survey time, processing time, data storage and is the underlying limit of automated algorithms. Lack of understanding of these systems makes defining point density in project specifications a complicated process. We are in the process of developing a method for determining the quantitative resolution of point clouds collected by a MMS with respect to known objects at specified distances. We have previously demonstrated the effect that scanner orientation in one axis, scanner configuration and scanner operating speed have on scan profiles. We have also focused on the effect on scan profiles of the combined vertical and horizontal rotations of the scanner (dual-axis rotations) and also incorporated point spacing for planar surfaces at different scanner mirror speeds, pulse repetition rates and field of view as a function of range into our model. The subject of this paper is to investigate the effect that a dual-axis scanner rotation has on profile spacing and to design a theoretical system to calculate the angular change on profiles exhibited on horizontal and vertical surfaces for different system configurations. The second goal of the research presented in this paper is to include in our calculations a method for incorporating surfaces that are not parallel to the direction of travel or that are not perfectly vertical, such as walls facing away from the road or sloped surfaces. Profile angle impacts on profile spacing and is a major factor in calculating point density on arbitrary objects, such as road signs, poles or buildings, all important features in asset management surveys. A number of tests were designed to investigate these issues and the results show that these tests have justified our methods, but it has been made apparent that vehicle dynamics play a larger role than anticipated.