Since the coordinate system in both photogrammetric and tacheometer measurements was the same (the same control points with the same coordinates were used), it was easy to match the surfaces created from the point clouds obtained by the photogrammetric and tacheometer measurements (Fig 7).
Judging from the cut section shown in figure 8, it might be stated that maximal deviation of the photogrammetricaly obtained point cloud compared to the one obtained by the tacheometer measurements does not exceed 2 mm (taking the largest area of deviations).
* High accuracy of measurements; the stated accuracy of the tacheometer used was 3 mm (though for normal laser scannersit seldom exceeds 4 mm);
* Despite the differences in the principles of measuring a single section of wing with the two different measurement methods, the deviations between the two methods did not exceed 2 mm, which is in the range of accuracy of method (tacheometer scanning) considered as the reference one.
* Instruments such as electronic tacheometers are widely used in geodesy, building construction, and other branches of industry, and they are therefore quite available.
The resulting calculated deviations of tacheometer readings are shown if Fig.
Still there can be noticed a tendency for decrease of the accuracy towards the limits of the measurements (-10[degrees] and 12[degrees]), which is quite common for the tacheometers both due to the errors of collimation at steep angles and the principle of action of vertical angle encoder of the tacheometer though more tests should be performed at that item too.
The calibration of accuracy of vertical angle measurement of Trimble 5503 tacheometer was performed using 1 m precise linear scale positioned at a distance of 2.4215 m to the instrument to be calibrated.
Similar method of angle measurement calibration could be implemented for all angle measurements, both vertical and horizontal of collimated instruments such as theodolites, tacheometers, etc.