Geoscience Reference
In-Depth Information
Fig. 16 Left accuracies comparison for raw (red) and calibrated data (blue). Right true lengths
for each vector provide by photogrammetry technique
improvement of the calibrated data of around 2 mm compared to raw data accu-
racy which is 4 mm. With 50 % improvement in accuracy, this study has math-
ematically proved the reliability of self-calibration to enhance the quality of TLS
measurements.
7 Conclusions
This study has employed a dense 3D target field (138 well-distributed targets
observed from seven scanner stations) to carried out a self-calibration of the
panoramic scanner (Faro Photon 120). The adjustment results have been evaluated
through residual graphs and statistical analysis procedures. Due to the magnitude
of calculated calibration parameters are very small, the plotted residual graphs
does not indicate any existence of errors except for constant rangefinder offset
error. However, significant tests were performed and the results have shown that
two (a
0
and c
0
) of four calibration parameters are significant. To investigate the
reliability of self-calibration, comparison has been made between RMS of resid-
uals for adjustment with and without calibration parameters. The results have
showed the ability of self-calibration with improvement in precision up to 29 %.
For accuracy assessment purpose, 14 vectors (from 15 test points) were established
using photogrammetry technique. These vectors (consider as benchmark) then
were used to computed the discrepancies (or accuracies) of vectors obtained from
TLS raw data and calibrated data. Based on the results, the improvement in
accuracy from raw to calibrated data was graphically and statistically presented.
With 50 % improvement in accuracy, self-calibration was mathematically proven
as significant procedure to enhance the quality of TLS data.
