The conceptual layout and data flow of a multi-sensor system for mapping applications is shown in Figure 1. The selection of sensors for such a system obviously depends on system requirements, such as accuracy, reliability, operational flexibility, and range of applications. The data acquisition module has, therefore, to be designed keeping both the carrier vehicle and the intended applications in mind. The data acquisition module contains navigation sensors and imaging sensors. Navigation sensors are used to solve the georeferencing problem. Although a number of different systems are used in general navigation, the rather stringent requirements in terms of accuracy and environment make the integration of an INS with GPS receivers the core of any sensor combination for an accurate mobile mapping system for short range applications. This combination also offers considerable redundancy and makes the use of additional sensors for reliability purposes usually unnecessary. However, the addition of an odometer type device, such as the ABS, for close-range applications may be useful for operational reasons, as for instance keeping a fixed distance between camera exposures.  Fig 1 Multi-sensor integration for mapping application The selected sensor configuration requires a certain data processing sequence. Part of the processing will have to be performed in real time, such as data compression for the imaging data and initial quality control processing for the navigation data. Most of the data, however, will immediately be stored for post-mission use. In post-mission, the data processing hierarchy is determined by the fact that all mapping data have to be georeferenced first before they can be used in the integration process. The first step is, therefore, the georeferencing of all mapping data and their storage in a multimedia data base. Although MMS can be air-based or land-based, however, the author will mainly use the land based systems to present the concept MMS for and will refer to the airborne systems where there are differences. |