Tuesday, September 20, 2016

By the Numbers: Positioning and Navigation


  • 4:  Number of individual positioning systems equipped on each of our 4 Mobile LiDAR systems: 1 dual antenna GPS/GNSS; 1 military-grade Inertial Measuring Unit (IMU); 1 Distance Measuring Instrument (DMI); and 1 GPS for vehicle navigation.
  • 200:  Frequency at which the vehicle’s position is updated every second (Hz).  The IMU fine-tunes initial positioning generated by the dual-antenna GPS/GNSS by combining readings attitude (pitch, yaw, roll) calculations with distance traveled (DMI) to produce an accurate position at 200 Hz.
  • 1:  Number of IMU’s onboard each Mobile LiDAR system.  One of our four IMU’s is also used by the U.S. Military as part of the guidance system of a Patriot Missile.  That system is regulated by the U.S. State Department through the International Traffic in Arms Regulations (ITAR) – needless to say, there’s a little bit of red tape to clear if we want to take that unit out of the country.
  • 12:  Number of miles of subterranean mine shafts surveyed during a previous project.  The combination of the IMU and DMI allow our systems to perform accurate collections during sustained GPS-outages using dead reckoning.  
  • 1,024:  Number of wheel rotation measurements performed every second.  Our DMIs are directly affixed to the vehicle’s wheel to ensure reliable readings. Due the inherent positional errors with GPS the DMI is not only used to indicate accurate distance traveled, but also to alert the system when the vehicle is stopped - called the "Zero Update".
  • 2:  The fluctuation in tire pressure (lbs.) which will result in inaccurate distance measurements.  During a collection, the DMI scale factor (a function of the tire's circumference) is constantly monitored and "calibrated" using other systems, including GPS.



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What is Mobile LiDAR?

Mobile LiDAR (Light Detection and Ranging) systems are comprised of vehicle-mounted lasers, cameras and GPS/INS navigation systems to capture highly-detailed and accurate three-dimensional (3D) topographic information for surveying and engineering applications. Michael Baker International became an early adopter of Mobile LiDAR technology by acquiring our first system in 2009, with further expansions in 2014 and 2015 that increased our fleet to four (4) Optech Lynx SG1 Mobile LiDAR systems. Over that period our systems have completed more than 300 projects throughout 29 different U.S. States (and multiple countries), and encompassing hundreds of thousands of miles. Our project portfolio includes applications in roadway design, 3D modeling, railroad corridors, signaled intersections, utility infrastructure, asset management, pavement condition assessment and airport infrastructure.