Accuracy of three-dimensional photogrammetry and cone beam computed tomography based on linear measurements in patients with facial deformities

Objectives: This study was aimed to investigate the accuracy of soft-tissue measurements obtained by two imaging modalities, three-dimensional (3D) photogrammetry and cone beam CT (CBCT) when confounded by influence factors (facial deformities and partitions). Methods: 60 wax facial models from facially deformed patients were captured by 3D photogrammetry and CBCT. 19 linear distances on each image were measured and juxtaposed to reference values attained via a coordinate-measuring machine (CMM) as the gold-standard. Paired t-tests were used to compare linear accuracy of the test and reference systems. The influence of deformities and partitions (created by dividing the face with three vertical and five horizontal lines) on the measurement errors were analyzed by independent sample t-test and one-way ANOVA. Results: Statistically significant differences were found between linear accuracy of the test and reference systems. The test values obtained by 3D photogrammetry were closer to the reference values than CBCT’s. 3D photogrammetry’s measurement errors were significantly higher in deformed areas, unlike CBCT’s. Both systems reported significantly lower errors within partitions 8 and 13 compared to other partitions; for CBCT, aside from partitions 8 and 13, the differences in the errors for partitions 6 and 10 were significant compared to partitions 8, 12, 13, 14. Conclusion: 3D photogrammetry showed a higher linear accuracy than CBCT in patients with facial deformities due to protuberances. Facial reconstruction by both test modalities was significantly influenced in different facial partitions, but facial deformities extensively affected the results from 3D photogrammetry.

Height Evaluation and Linear Accuracy of Digital Level, Total station, GPS and Orthophoto

In this research, Digital level (DL), Total station (TS) and GPS were used to assess accuracy and precision of the height component. Field observations were implemented in two tested areas. A reference network which consisted of 34 points on area1 and 10 control points on area2 which had been observed five times using Digital level, RTK-GPS and Total station (TS) where Digital level was considered as a base for comparison. Several known control points were used as check points to evaluate the accuracy of measurements. According to the obtained results, TS and GPS-RTK measurements were compared with the adjusted reference points measured by precise Digital level (DNA 03). Around ±15 mm standard deviation for TS and ±13.5 mm for GPS were achieved. Linear accuracy of TS, GPS, and orthophotos measurements from Vossing German Company were also investigated in regular features within the same tested areas. The actual lengths were measured with steel tape up to a millimeter accuracy and were considered as being a base for comparing. The maximum deviation 22mm accuracy has been obtained in area2 and 12 mm in area1. The study shows that the extracted features from orthophotos had less accuracy in hilly regions due to relief displacement whereas they were more accurate in gentle slopes.

Accuracy Test of Laser Tracker under Condition of Air Turbulence

Laser tracking for interior industrial metrology is discussed. In this work, the effects of air turbulence on the angle of laser wave propagation is analyzed in the absence of the effects associated with other meteorological parameters (pressure, humidity) and particulate pollutants (dust, smoke). This analysis establishes the effectiveness of laser tracking under turbulent air conditions and quantification of deviations in the angular and linear accuracy from those provided by the manufacturer. An experimental setup and associated measurement method to determine the turbulence structure coefficient are described. It was found that turbulent air conditions resulted in a radical decrease in measurement accuracy. The reduction in accuracy was evidenced by a decrease in power and an increase in standard deviation of the laser beam, as well as a decline in the angle and distance measurement precision. The experimental measurements show a high correlation to predicted values.