Table A3.

Potential sources of error

Error sourceComments
Noise in the captured video frames
Lens distortionThe camera alignment procedure in PhotoScan determines internal camera parameters through self-calibration, which can be less effective than a laboratory-type camera calibration. A virtual set of camera locations with convergent geometry was employed to minimize this error.
Scanning distortionAlthough a high frame rate was used (60 fps progressively scanned), this type of rolling shutter means very rapid movements can be offset from one edge of the charge coupled device (image sensor) to the other.
Poor placement of the camerasParticularly important with only two cameras. The spacing and angles of the cameras relative to the slope surface can influence the accuracy of the resulting 3D measurements.
Errors in the physical measurement of the photogrammetric markersThe measurements are within <1 mm.
Errors in the placement of the photogrammetric reference markers in each of the captured video framesPlacements are within <1 mm.
Differences in lighting
Differences in surface texture