Two kinds of survey were done: Lab Survey and Field Survey. In the lab survey three different surfaces were scanned: flat (black and white poster), spheres (50 mm diameter) and gravel (40 mm to 60 mm of average diameter - D50). The laboratory “study area” was inside a
tray 1 m x 1 m able to contain gravel or artificial spheres. The tray was scanned for each sample and subsequently, through Cyclone software a square of 0.80 m x 0.80 m was extracted and subsequently analysed. This reduction in the area of analysis was necessary to avoid boundary influence (of the tray) in the final results. The field surveys were on two different patches 1m x 1m of the Feshie River. As for the lab experiment the patches were reduced to 0.80m x 0.80 m. A geo-orientation of each TLS scan was introduced to allow the comparison of the same surface among the different scan repetitions. Targets and an Imaging Station were used to allow the geo-orientation of the TLS clouds.
The TLS experiments are divided into two main types: range experiments and moving experiments. The first kind compares the DEMs of the same surface derived from different scan distances, whereas the second one compares the results of the same surface from different scanner and control targets dislocation.
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RANGE EXPERIMENTS
The range experiments are divided into vertical and horizontal experiments. In this analysis the scanner and the control targets were fixed, whereas the angle of incidence changed from normal to oblique from the first to the second kind of survey.
FIXED SCANNER,FIXED CONTROL TARGETS, NORMAL ANGLE OF INCIDENCE
Flat and sphere surface: 10 scans of the same patch at different distance: 10 m, 15 m, 20 m
The results of this experiment are useful to analyse the loss of detail in relation to the distance and identify a threshold distance to have a good roughness estimation. The maximum distance to use depends on the type of TLS used (short or long range). The vertical disposition of the surface allows not to have effects of the angle of incidence.
The flat surface used was 1/2 black and 1/2 white to verify the effects of different colour intensity (Figure 29). FIXED SCANNER
FIXED CONTROL
Figure 29. Normal range experiments.
FIXED SCANNER,FIXED CONTROL TARGETS, OBLIQUE ANGLE OF INCIDENCE
Flat, spheres, gravel surface and Feshie patches: 10 scans of the same patch at different
distance: 5, 10, 15 m, 20 m. The results of this experiment could be useful to analyse the loss of detail in relation to the distance and identify a threshold distance to have a good estimate of roughness. The maximum distance to use depends on the TLS model (short or long range). The horizontal disposition of the surface allows to quantify the effects of the angle of incidence through comparison with the scan of the same surface in a vertical disposition (normal angle of incidence). The flat surface used was 1/2 black and 1/2 white to verify the effects of different colour intensity (Figure 30).
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FIXED SCANNER
Figure 30. Oblique range experiments.
MOVING EXPERIMENTS
The moving experiments are divided divided into moving targets, moving TLS and moving both. In this experiment the scanner and the control targets were moved whereas the range and the angle of incidence was fixed.
RANDOM ERROR :FIXED SCANNER,MOVED CONTROL TARGETS
Flat, spheres, gravel surface and Feshie patches: 9 TLS surveys at 10 m of horizontal
distance. The TLS was in the same positions, but the control targets relocated randomly and the scans registered individually before comparison (Figure 31).
FIXED SCANNER MOVED CONTROL
Figure 31. Targets moving experiments.
These experiments, could be useful to quantify the random errors due to relocating the scanner, the control targets and the registration process.
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SCENE ERROR :MOVED SCANNER,FIXED CONTROLS
Flat, spheres and gravel surface: 10 TLS surveys at 10 m of horizontal distance. The TLS
was in a random position, the control targets in the same positions and the scans registered individually before comparison (Figure 32).
MOVED SCANNER FIXED CONTROL
Figure 32. Scanner moving experiments.
The use these types of surface, it is important to analyse errors on different degree of roughness. This experiment can be useful to identify some rules of TLS positioning in relation to the roughness degree.
RANDOM AND SCENE ERROR:MOVED SCANNER,MOVED CONTROLS
Flat, spheres, gravel surface and Feshie patches: 10 TLS surveys at 10 m of horizontal
distance. The TLS was in a random position and also the control targets in a random position for each scan. Individual scans registration before comparison (Figure 33).
MOVED SCANNER MOVED CONTROL
Figure 33. Scanner and targets moving experiments.
N.B. The internal set up (density, speed, etc.) of the TLS must be the same for all the experiments.
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EXPERIMENTS SUMMARY
The different experiments carried out can be summarized as shown in table 2, while Figure 34 shows the different kinds of surfaces.
Table 2. Different kind of experiment carried out with different surface: Flat, spheres, gravel, Feshie patch 1
and Feshie patch 2.
Gravel Spheres Flat
Range Feshie Patch 1 Feshie Patch 2 Feshie
Figure 34. Surfaces scanned.
FLAT SPHERES GRAVEL FESCHIE P1 FECHIE P2
10m NORMAL ANGLE OF INCIDENCE 20 10 - - - 30
15m NORMAL ANGLE OF INCIDENCE 10 10 - - - 20
20m NORMAL ANGLE OF INCIDENCE 10 10 - - - 20
5m OBLIQUE ANGLE OF INCIDENCE - - - 10 10 20
10m OBLIQUE ANGLE OF INCIDENCE 10 10 10 10 10 50
15m OBLIQUE ANGLE OF INCIDENCE 10 10 10 10 10 50
20m OBLIQUE ANGLE OF INCIDENCE 10 10 10 10 10 50
FIXED SCANNER, MOVED TARGETS 10 - 9 - - 19
MOVED SCANNER, FIXED TARGETS - - 9 - - 9
MOVED SCANNER, MOVED TARGETS - - 9 10 10 29
TOTAL 80 60 57 50 50 297 TOTAL SURFACE EXPERIMENTS R A N G E EX P ER IM EN TS M O V IN G EX P ER IM EN TS
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