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Using inertially-aided real-time kinematic technology as a land-based mapping tool
 Manfred D. M. Sever  Frank A. Artés Applanix Corporation, 85 Leek Crescent Richmond Hill, Ontario, Canada. L4B 3B3 Tel: 905-709-4600, Fax: 905-709-6027 Email: msever@applanix.com, artesf@applanix.com Introduction – mapping, a traditional methodology Producing detailed mapping data has traditionally been an aerial survey practice using standard photogrammetric methodology. Generating accurate cartographic data from aerial photography is a well-established technology with its roots stretching back to the last century. Using conventional survey instrumentation, such as total station technology, to locate and identify map-based information has also been used with success, but can be very time consuming. The continued drive for greater accuracy and increased productivity has always been present in the survey and mapping field, with advances in technology both hardware and software-based, making great strides in this regard. However, one fundamental remains unchanged. The ability to see the features one is trying to map often lies at the root of the accuracy issue. If the features are clearly visible on the aerial photography the chances of precisely positioning the data using today’s analytical and softcopy photogrammetric technology is virtually 100% assured. However, if feature identification is hampered by a dense vegetation canopy, or the relief displacement of tall buildings, dark shadow areas, or multi-level road and highway networks, then accurate data positioning is not possible using aerial photography alone. Land-based mapping technology is proving to be the solution to this problem. Land-based mapping for transportation planning and GIS database feature acquisition Transportation planners require current information on road location, surface condition, road centerline position, and details on the multitude of highway signage related to transportation routes. In addition, GIS professionals also require information on the placement of various utility infrastructure features, such as hydro poles, fire hydrants, manholes and drainage catchbasins etc., to help them plan, maintain and predict various scenarios based on asset location and condition. The majority of these features are often associated with dense urban environments where one is likely to encounter urban canyons, tree-lined streets with overhanging foliage, underpasses and elevated roadways. Land-based GPS positioning has been used with marginal success as a mapping data acquisition tool to accurately position planimetic features in open, unobstructed areas. Commercial users of GPS systems generally find under ideal conditions a GPS system will offer excellent positional accuracy, however, this approach remains ineffective in a dense urban environment. GPS satellite shading and dropout, the result of tall buildings blocking reception, and multipath issues generated by signals bouncing off reflective surfaces, cause stand-alone GPS systems to be completely inadequate in obtaining reliable positioning information in a downtown core area. Vehicle-mounted mobile GPS positioning is further complicated in urban or tree canopy areas as the structures that cause poor GPS reception also cause the satellites to go in and out of view, limiting a GPS receiver’s ability to provide continuous, accurate positional information. The POS LV system alternative Following a GPS dropout or phase lock outage, a typical land-based dual frequency GPS receiver requires 30 to 120 seconds of reacquisition lock before providing RTK (real-time kinematic) level accuracy. During this time period, particularly if using a mobile land-based system, the accuracy of the data generated for position determination degrades very quickly, effectively making the system unusable. An alternative land-based system designed to accurately position all difficult-to-locate cartographic features, such as those associated with mapping for transportation planning, or planimetric data-gathering for GIS databases, is now available. The Applanix POS LV system is an aided inertial navigation system designed specifically for precise position and orientation measurements for survey and vehicle control applications. The system utilizes IARTK (Inertially-Aided Real-Time Kinematic) technology, providing continuous position and attitude data under the most demanding and difficult GPS conditions. A mobile mapping vehicle equipped with the POS LV system allows the operator to generate reliable and precisely positioned map data in areas where known GPS outages are routinely encountered, such as those found in a city’s urban canyons. Mapping roads and road corridors in a modern city where highrise buildings are commonplace, or generating map data for multilevel highways, or centerline road mapping under bridges and in tunnels, present the POS LV system with little problem. Likewise, heavily forested areas and mountainous terrain, locations which are particularly susceptible to GPS outages, can be successfully mapped with a degree of accuracy previously unavailable.
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