The LiDAR uncertainty budget part III: data requirements

Part I of this series described the LiDAR georeferencing process (for one, 2D, single return scanner). Part II showed how point uncertainties are computed and why they are useful.

What hasn’t been covered so far is what data you need to do this stuff! Here is your shopping list:

Scanner data

  • Raw LiDAR ranges
  • Scanner mirror angles
  • Waveforms with times if you are going to decide range-to-returns for yourself
  • Intensity
  • anything else (RGB, extra bands, etc)

Essentially you need the full data package from the LiDAR including any corrections for mirror wobble or other sensor oddness – and a way to decode it. You also need engineering  drawings which show the LiDAR instrument’s reference point.

Aircraft trajectory data

  • GPS/GNSS based aircraft trajectory (positions in space)
  • Attitude data  (relationship between the aircraft’s orientation and some reference frame) normally collected by a ‘strapdown navigator’ – which is an inertial motion sensor (often called IMU), and often integrated with GNSS.

Hopefully you don’t have to do the work combining these yourself, but you need a high-temporal-resolution data stream of position (XYZ) and attitude (heading pitch roll, or omega phi kappa, or a quaternion describing rotation of the airframe relative to the earth). This needs to be as accurate as possible (post-processed dual-frequency GPS with preferably tightly-coupled processing of IMU and GPS observations).

Navigation instrument and aircraft data

  • Engineering drawings which show the navigation instrument’s reference point
  • The lever arm between the navigation instrument reference point and the LIDAR reference point, in IMU-frame-coordinates
  • The rotation matrix between the IMU and the LIDAR coordinate systems
  • If necessary, the rotation matrix describing the difference between the aircraft’s body frame and the IMU’s internal coordinate system (quite often, this gets simplified by assuming that the IMU frame and the aircraft frame are equivalent – but many operators still account for this – which is awesome!)
  • Any boresight misalignment information you can get (tiny angles representing the difference between how we think instruments were mounted and how they actually were mounted)

Of course, you could also just push your contractors to deliver point-by-point uncertainty or some per-point quality factor as part of the end product.

This series might have one more post, on how to deal with these data – or more accurately a tutorial on how not to. And then I run out of expertise – brain = dumped, and over to people with newer, more up to date experience.