1. GPSVisionTM Overview
Accurate positioning and the identification of transportation and other infrastructure (e.g., a traffic sign, the curb line) can be an immense task requiring the efficient collection of vast quantities of data. New technologies offer opportunities to greatly improve the effectiveness of mass and incremental data collection. One of the newly developed technologies for collecting infrastructure data is GPSVisionTM (Figure 1), which utilizes Navstar GPS integrated with an INS and two state-of-the-art progressive scan CCD (charge coupled device) cameras. The result is that any object that is "seen" by the sets of cameras can be precisely located using a stand-alone global coordinate system in conjunction with Lambda Tech’s advanced soft-photogrammetric mathematical model.
Fig. 1 The GPSVisionTM Mobile Mapping System
GPS provides accurate position data to the GPSVisionTM system. Because of low data rates (1Hz) and the requirement of viewing at least four satellites, the use of GPS alone is limited. In contrast, INS provides high rate position (X, Y, Z coordinates) and attitude (direction) information (100Hz), but its sensor errors tend to grow with time. By integrating GPS and INS, the accurate GPS position is used to update the INS, and the INS then produces the high rate, accurate position and attitude data of the GPSVisionTM system, even when the GPS signals are lost.
From a photogrammetric perspective, GPSVisionTM is a fix-based stereo vision system with known position and attitude provided by the GPS/INS component. Just as a person uses two eyes to determine the distance of an object, every infrastructure feature that is "seen" by the cameras can be triangulated into a three dimensional coordinate and then transferred into a global coordinate system (e.g., latitude, longitude, height).
From an application perspective, the GPSVisionTM system is used to collect digital images along highways, state roads, residential streets and/or railroads while traveling at posted speed limits. Every image is tagged with its position and attitude determined by the GPS/INS component. These georeferenced digital images are used for videolog applications. Most importantly, the stereo images are also designed to be accessed by Lambda Tech’s unique Feature Extraction Software to position visible physical features, such as curb lines, traffic signs, manholes, pedestals and building locations. In addition, the GPS/INS positioning component creates base maps of the street network for GIS base map applications.
The georeferenced digital image data and the position and attribute data of the features are stored in a simple format that can be used in standard GIS systems.
Once the processed data is loaded into the target GIS, the data is easily displayed in map format, analyzed and/or manipulated utilizing GIS database query functions. A typical client can use this data to accurately position items of infrastructure, develop base maps or view image data directly from an operator’s personal workstation in the vehicle or in the office.
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