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.