3D Mapping With Multiray Photogrammetry
Business-changing hardware and software innovations are being announced almost daily in the geospatial world. Although sometimes it seems like these ideas are new, in reality they are the culmination of decades of behind-the-scenes development and research. Incremental changes in each software and hardware release build on others and lead to more ways of addressing problems, often more quickly, more effectively and less expensively.
Over the past 10 years, LiDAR has become the technology of choice for deriving highly accurate terrain data and 3D models, and it is commonly used for a variety of mapping applications in markets as diverse as forestry and transportation. At the same time, the rapid adoption of digital aerial cameras and the movement toward fully digital workflows has changed aerial mapping forever. The significant improvements that have been made in the radiometry, accuracy and resolution of digital aerial data; the increased volume of data that can be collected due to the larger swath width and onboard storage; and the processing software that allows more automation to produce a variety of end products more quickly than in the past has led to the development of many new applications.
The hardware and software used to collect and process digital aerial images has evolved to the point where very dense point clouds and accurate digital surface models (DSM) and digital terrain models (DTM) can be automatically generated from multiple overlapping aerial images using multiray photogrammetry. Conceptually, multiray photogrammetry is not new; academia has been experimenting with the technology for years. The difference is that today there are cameras capable of collecting data with sufficient forward and side overlap and density to generate point clouds using highly automated workflows.
One example is the family of Microsoft UltraCam digital aerial systems and Microsoft UltraMap 3.0 workflow software. First developed in 2007 to create 3D city models for the Virtual Earth database, UltraMap is now used to support Bing Maps. Over the past five years, the functionality has been enhanced until it is feasible to reach the accuracy and detail demanded by customers in automatically generated DSM and DTM.
“Multiray photogrammetry relies on obtaining a highly redundant dataset of multiple overlapping images that allows for aerial triangulation and automated ‘dense matching’ of points,” said Alexander Wiechert, Microsoft business director. “The resulting point cloud has easily a point density of several hundred points per square meter, compared to LiDAR data that is around 10 points per square meter. The camera also has a usable swath 2.5 times wider than a scanner, and the airplane can fly faster, which makes the whole process more cost effective.”
Multiray photogrammetry is highly suitable for many applications, including national mapping and urban mapping. In many situations it is faster and less expensive than collecting LiDAR, although LiDAR technology has several other capabilities, such as vegetation penetration for forestry and utility line detection for corridor management that cannot be replicated by digital aerial cameras. The mapping community benefits from having more options to pick the most suitable data and processing method for each project.
“The convergence of digital aerial camera technology and processing software capabilities, after many years of expert development, allows us to offer new advanced products that will support expansion of the 3D mapping market,” said Jerry Skaw, director of UltraCam sales and marketing in North America. “The demand for data is only going to increase, so if we can provide a more cost-effective option while maintaining high quality, it helps everyone.”
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