VISAT: Mapping what you see
With the continued growth of urban centers all around the world, city planners are required to keep up with up-to-date geographical at a faster rate. This has led to the establishment of spatially-referenced Geographic Information Systems (GIS) for a variety of municipal applications. This information, however, is expensive to obtain by conventional methods. In addition, conventional methods supply only point solutions and are therefore not suited to support the increasingly complex requirements posed by urban centers in a timely fashion. Satellite remote sensing and aerial photogrammetry are two methods which can provide various GIS information at high rates and reasonable cost. However, with the first method, the associated accuracy is not suitable for many applications, and in the second case the near vertical field of view provides only part of the information required.
Furthermore, the type and quality of information required by the user is changing, quite often the user prefers a cartographically less perfect product (e.g. map substitute) that contains the most recent information rather than a product of very high cartographic standard but with outdated information. Also, the demand for user specific maps or data and for noncartographic products such as reports, images, graphs, and frequently asked questions are steadily increasing. For example; 3D digital maps (with landmarks; road vectors; transportation infrastructure information; etc.) that offer more visual information to make car navigation easier will soon replace the conventional 2D maps. 3D digital maps with enhanced 3D visualization will make maps even more attractive, informative and attractive, informative and interesting, supporting a new range of Internet and consumer applications.
With the advances in satellite and inertial georeferencing techniques and the readily available of digital imaging sensors, a considerable portion of GIS information can be acquired from moving vehicles. The advantage of kinematic-mode data collection is that the survey can be performed much faster and therefore more economically, whilst gathering mapped data from a new dimension – in the same plane where the data is seen and needed, or what the human eye sees.
Mobile Mapping – The venue for 3D Mapping
The concept of mobile mapping or mapping from moving vehicles has been around for as long as photogrammetry has been practiced. Early incarnations of Mobile Mapping Systems (MMS) were however, restricted to applications that permitted the determination of the mapped from existing ground control points. Fifteen years ago, advances in satellite and inertial location technologies made it possible to develop mobile mapping system differently. Instead of using ground control as reference for orientating the images, the trajectory and attitude of the imaging platform could now be determined directly. This made mobile mapping to be independent of preset ground control points. Hand in hand with this development was the change from analog to digital imaging- a change that has considerably evolved over the past years (Schwarz and El-Sheimy, 2004). As a result, mobile mapping systems have evolved from a concept of academic interest to a commercially viable industry and are currently at industry and are currently at a point where they match classical survey techniques in accuracy but far surpass in economy, speed and efficiency. These systems integrate navigation sensors and imaging sensors to determine the positions of the imaged points.. Although, the idea of mobile mapping is based on a simple concept, the real world implementation brings a lot of challenging problems. These are a product of integrating the concepts of kinematic geodesy, navigation, remote sensing, machine vision, and digital photogrammetry sciences which have been always treated separately. For more details, the reader is advised to read the article by Skaloud (1999) on mobile mapping implementation problems.
The initial trials to build a Mobile mapping system was a van for highway inventory (HI) 1983 by the University of Calgary (Schwarz et. al. 1993), however real implementation of practical systems were developed by the Centre for Mapping at the Ohio State University and the University of Calgary in the mid nineties. The University of Calgary system development objective was “A mobile mapping system that positions all visible objects of interest for an urban GIS with an RMS accuracy of 0.3 m while moving through a road corridor at a speed of 60 km/h and a maximum distance to the desired objects of 50 m. Data acquisition must be automatic and should contain real-time quality control features. Data processing, except for quality control, will be done in post mission and should have separate modules for georeferencing, image data base management, imaging, and quality assessment.” (El-Sheimy, 1996) The outcome of this project was the VISATT Van. The VISATT system – in its initial form – was notable because of the large number of imaging sensors it employed. Where previous land-based MMS were simple stereovision systems employing only two forward facing cameras, VISAT had eight cameras – permitting more flexible data collection and better imaging geometry. A new generation of the VISATT Mobile Mapping System has been developed in cooperation with Absolute Mapping Solution (AMS) which truly delivers a mobile mapping platform that integrates multisensors subsystems (See Figure 1).
In this article, an overview of the VISATT van is given. The sensors on board the VISATT are described highlighting their system functionality while providing an overview of the system’s operational mapping cycle. System deliverables and accuracy are discussed. Finally, an outlook into the future development of the VISATT including hardware, software, and applications is presented.