Production of Als and RGB/CIR True Ortho Images

Production of Als and RGB/CIR True Ortho Images


Alexander Wiechert
Alexander Wiechert
Managing Director
TopoSys GmbH, germany
[email protected]

Airborne Laser Scanner Systems (ALS) are well known since years. Most of them use a kind of rotating or oscillating mirror as a mean for beam deflection. This paper presents a much more reliable and accurate concept of laser beam deflection and shows case studies of projects of so called high precision laser scanning

To calculate an elevation model from data acquired by an airborne laser scanner (ALS or Lidar) one needs to know four basic parametres (Figure 1):

  • Distance from the sensor to the ground/object
  • Sensor position
  • Sensor orientation (attitude)
  • Beam deflection

But knowing these parametres as good as possible will not automatically lead to a perfect elevation model. Due to the nature of the measurement principles, an airborne Lidar measurement is always a measurement from a random reflector which can not be repeated. So, an individual measurement is not reliable and highly reliable elevation models can only be achieved by processing a lot of adjacent measurements.

Fig 1 General Principle Of Airborne Laser Scanning (ALS)