Dr Ayman F Habib
Department of Geomatics Engineering, University of Calgary, Canada
Since its inception in the early eighties, Mobile Mapping Systems (MMS) have gone through significant advances related to the acquisition hardware, processing software, and range of applications. These advances are posing new challenges to the mobile mapping community. This paper outlines the current challenges facing the mapping community in this regard
Over the past few decades, there has been a growing need for digital land-related spatial data and information to populate GIS databases for a wide range of civilian and military applications. The primary challenge for satisfying such a need is providing current, detailed, and accurate data at a reasonable price. Mobile Mapping Systems (MMS) were developed in the early eighties to do exactly that. Since its introduction, MMS have been used to map and inventory various transportation routes and utility systems. Also, they are heavily involved in data collection in support of natural resource management, decision making, and environmental monitoring activities.
MMS: Data Acquisition Systems
As mentioned earlier, a MMS is equipped with a positioning unit, which is capable of inferring the system’s location and attitude throughout the mapping mission. The purpose of the positioning unit is to directly provide the geo-referencing parameters, which describe the position and orientation relative to a global reference frame, for the other system components (e.g., the imaging unit). Thus, the positioning unit helps in reducing and even eliminating the need for external control information to indirectly geo-reference the mapping platform. The persistent development in GPS and INS technologies is allowing for the derivation of the system’s position and attitude with very high accuracy (few centimeters and few arc seconds).
Achieving the full benefit of the directly measured geo-referencing parameters depends on the quality of the calibration coefficients describing the internal characteristics of the imaging and other system components together with the spatial and rotational offsets between the individual measurement units onboard the MMS. In this regard, one needs to emphasize that the calibration of a MMS is more critical than that for traditional mapping systems based on indirect geo-referencing procedures (i.e., using external ground control points). The significance of the calibration parameters is attributed to the fact that indirect geo-referencing procedures can compensate for inaccurate calibration by modifying the estimated geo-referencing parameters to assure the best fit at the available control. On the other hand, a MMS with direct geo-referencing capabilities do not allow for any compensation to inaccurate calibration parameters.
Fig 1: (a) The two dimensional array in the focal plane of a frame camera (b) is replaced by a single linear array in a line camera.
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