Full-waveform ALS workshop - Georeferencing of ALS Data

Sixth Presentation

Norbert Pfeifer: Georeferencing of ALS Data


Overview:

• Multi Sensor System
• Errors
- Data driven point of view
- Components of the system
• Mathematical models for correction
- Model driven approaches
- Approaches not considering the measurement process
• Observation of discrepancies
• Examples
• Summary / Points of further discussion




Summary:

• Elevation- and planimetric-coordinates of the “original” points on the ground and upon objects are
affected by systematic errors caused by the GPS/INS/Laser scanner system. 􀃆 This leads to
erroneous georeferencing. (direct georeferencing)
• Errors may be static or dynamic and global or varying from strip to strip.
• First quality check: Computation of differences in the strip overlap
• Elevation in height alone is not sufficient
• 3D correction of exterior and interior orientation (calibration) is necessary
• Solution: ALS strip adjustment with rigorous mapping function (polar measurement and trajectory from
GPS/INS with tie patch parameters)
- Minimization of errors at autoamtically determined homologous objects (planes)
- Quality parameters (improvement of std.dev. After adjustment)
• For high precision demands (relative and absolute accuracy) ground control is required.
• Flight planning must consider cross strips and control point areas.
• Quality control is a must for each block! Graphic display of the discrepancies is a thorought check for
detecting systematic errors (excluding the datum).
• Future aims: Standardization in ALS
- GPS/IMU preprocessing
- Fligh parameters: strip overlap, flight patterns (cross strips)
- Quality of ALS data should be estimatable a priori (as for image-based AT)