Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...
Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ... Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...
64 3. Calibration of Terrestrial Laser ScannerTable 3.14: Error of the horizontal axis derived by measurements in two faces to targets installed at different verticalangles.Setup Point Number Vertical Anglev [°] Error of Horizontal Axis i [°]1 1 15 -0.0832 64 -0.0643 86 -0.0484 112 0.0515 140 0.0016 164 0.0052 1 54 0.0342 72 0.0043 81 -0.0524 114 0.0865 145 0.067pecially regarding the eccentricity. A conceivable eccentricity may influence the interpretation significantly.The experimental setup has to be improved so that with different constant vertical directions and growingranges, the investigation has to be repeated.The setup for the examination of the collimation axis mayprovide some indications, with the difference that the lines of sight do not run horizontally but vertically.3.5 Non-Instrumental ErrorsLaser scanning technology is based on performing measurements on various kinds of objects.Since theuse of prisms isnot necessary, nor recommended, the distances to be measured are affected by severalparameters, such as the intensity of the reflected laser beam, the angle of incidence, surface properties,e.g.colour and roughness, multipath, speckle effects, etc. In the following, some of these parameters arediscussed and investigated.3.5.1 Intensity of Laser BeamThe intensity of the reflected laser beam is of importance since the amplitude of the received signal iscorrelated with the quality of the detecting range. The better the signal-to-noise ratio, the better the deter¬mination of the distance. The intensity (I) is influenced by three parameters:• the range d(I~jp),• the reflectivity of the object, and• the angleof incidence.Figure 3.37 shows the development of the intensity relative to a maximum. The upper figure indicatesthe relation between the range and the intensity for different reflectivity values. The longer the range andthe lower the reflectivity of the object, the less the intensity. The lower figure presents the intensity of atarget with a reflectivity of 90 % and shows that the intensity also decreases systematically. For example,the intensity line of the target with a reflectivity of 20 % corresponds to the intensity line to a target with areflectivity of 90 % and an anglevalues and low angles of incidence.of incidence of 30 °. Theintensity worsens with respect to low reflectivity
3.5 Non-Instrumental Errors 651 o08&06vic0)I 0402001 008v>c0)I 0402°°0 5 10 15 20 25 30 35 40 45 50range [m]Figure 3.37: Intensity of reflected laser beam. Influence of the reflectivity (top) and influence of the angle of incidence(bottom).The relative intensity values in Figure 3.37 do not match the given reflectivity values of the targets. Upto 5 m, the white target shows a relative intensity of « 93 %, the grey target shows a relative intensity of« 52 % and the dark grey target shows a relative intensity of « 38 %. Thus, the given reflectivity valuesindicate system-related reflectivity values more than absolute reflectivity values.Concerning the intensity of laser light, the speckle effect also has to be considered. Specklesare based onvariations of the intensity of coherent laser light produced by the interference of the diffuse scattered lighton rough surfaces with the incident light.This means the intensity of the reflected laser light can varydepending on the intensity of rough surfaces and can be affected by speckle effects.3.5.2 Angle of IncidenceThe angle of incidence is defined as the angle between the incident laser beam and the tangenton the surfacefrom which the laser beam is reflected. Generally, the angle of incidence can be measured in two directions,horizontally and vertically. An angle of incidence of 90 ° describes a laser beam hittingobjectat a normal.the surface of theThe angle of incidence influences the distances to be measured in two different ways.On one hand, thecenter of reference for the distance is shifted because the footprintof the laser beam varies from a circularform to an elliptical form. On the other hand, the footprint of the laser spot increases and covers a largerarea. The reference point for measuringthe distance is shifted and not well-defined because of the distortionof the footprint. Thus, the distance has a systematic offset leading to a false range between objectand laserscanner. Furthermore, the noise of the distances increases with a decreasing angle of incidence because theintensity of the reflected laser beam decreases and the footprint of the laser beam enlarges.
- Page 24 and 25: 14 2. Components of Terrestrial Las
- Page 26 and 27: 16 2. Components of Terrestrial Las
- Page 28 and 29: 18 2. Components of Terrestrial Las
- Page 30 and 31: 20 2. Components of Terrestrial Las
- Page 32 and 33: 22 2. Components of Terrestrial Las
- Page 34 and 35: 24 3. Calibration of Terrestrial La
- Page 36 and 37: 26 3. Calibration of Terrestrial La
- Page 38 and 39: '28 3. Calibration of Terrestrial L
- Page 40 and 41: 30 3. Calibration of Terrestrial La
- Page 42 and 43: 32 3. Calibration of Terrestrial La
- Page 44 and 45: "[m] of system 90%) 3540 distance b
- Page 46 and 47: !36 3. Calibration of Terrestrial L
- Page 48 and 49: 138 3. Calibration of Terrestrial L
- Page 50 and 51: 40 3. Calibration of Terrestrial La
- Page 52 and 53: 42 3. Calibration of Terrestrial La
- Page 54 and 55: 44 3. Calibration of Terrestrial La
- Page 56 and 57: 46 3. Calibration of Terrestrial La
- Page 58 and 59: 48 3. Calibration of Terrestrial La
- Page 60 and 61: 50 3. Calibration of Terrestrial La
- Page 62 and 63: 52 3. Calibration of Terrestrial La
- Page 64 and 65: 54 3. Calibration of Terrestrial La
- Page 66 and 67: 56 3. Calibration of Terrestrial La
- Page 68 and 69: Inormal axis,intersectionpoint axis
- Page 70 and 71: 60 3. Calibration of Terrestrial La
- Page 72 and 73: 62 3. Calibration of Terrestrial La
- Page 76 and 77: j/-*'.-,•66 3. Calibration of Ter
- Page 78 and 79: 68 3. Calibration of Terrestrial La
- Page 80 and 81: 70 3. Calibration of Terrestrial La
- Page 82 and 83: 72 3. Calibration of Terrestrial La
- Page 84 and 85: 74 4. Static Laser Scanning4.1.2 Mi
- Page 86 and 87: 76 4. Static Laser ScanningOptical
- Page 88 and 89: 78 4. Static Laser Scanningmaximum
- Page 90 and 91: 80 4. Static Laser Scanningand gene
- Page 92 and 93: 82 4. Static Laser Scanning• Ther
- Page 94 and 95: 84 4. Static Laser Scanning4.3.3 NU
- Page 96 and 97: 86 4. Static Laser Scanning
- Page 98 and 99: 88 5. Kinematic Laser Scanningmirro
- Page 100 and 101: 90 5. Kinematic Laser ScanningThe a
- Page 102 and 103: 92 5. Kinematic Laser Scanninghas a
- Page 104 and 105: '94 5. Kinematic Laser Scanningbeam
- Page 106 and 107: —96 5. Kinematic Laser ScanningTa
- Page 108 and 109: ''iI98 5. Kinematic Laser ScanningA
- Page 110 and 111: 40323 o.o; 50545 aT [jjs] 1.0().2 S
- Page 112 and 113: 102 5. Kinematic Laser Scanning5.3
- Page 114 and 115: —1.104 5. Kinematic Laser Scannin
- Page 116 and 117: propagationresults series Taylorter
- Page 118 and 119: 108 5. Kinematic Laser Scanningonly
- Page 120 and 121: cf.aroundframe regardingsetupusinga
- Page 122 and 123: 112 6. Applications of Terrestrial
64 3. <strong>Calibration</strong> <strong>of</strong> <strong>Terrestrial</strong> <strong>Laser</strong> <strong>Scanner</strong>Table 3.14: Error <strong>of</strong> the horizontal axis derived by measurements in two faces to targets installed at different verticalangles.Setup Point Number Vertical Anglev [°] Error <strong>of</strong> Horizontal Axis i [°]1 1 15 -0.0832 64 -0.0643 86 -0.0484 112 0.0515 140 0.0016 164 0.0052 1 54 0.0342 72 0.0043 81 -0.0524 114 0.0865 145 0.067pecially regarding the eccentricity. A conceivable eccentricity may influence the interpretation significantly.The experimental setup has to be improved so that with different constant vertical directions <strong>and</strong> growingranges, the investigation has to be repeated.The setup for the examination <strong>of</strong> the collimation axis mayprovide some indications, with the difference that the lines <strong>of</strong> sight do not run horizontally but vertically.3.5 Non-Instrumental Errors<strong>Laser</strong> scanning technology is based on performing measurements on various kinds <strong>of</strong> objects.Since theuse <strong>of</strong> prisms isnot necessary, nor recommended, the distances to be measured are affected by severalparameters, such as the intensity <strong>of</strong> the reflected laser beam, the angle <strong>of</strong> incidence, surface properties,e.g.colour <strong>and</strong> roughness, multipath, speckle effects, etc. In the following, some <strong>of</strong> these parameters arediscussed <strong>and</strong> investigated.3.5.1 Intensity <strong>of</strong> <strong>Laser</strong> BeamThe intensity <strong>of</strong> the reflected laser beam is <strong>of</strong> importance since the amplitude <strong>of</strong> the received signal iscorrelated with the quality <strong>of</strong> the detecting range. The better the signal-to-noise ratio, the better the deter¬mination <strong>of</strong> the distance. The intensity (I) is influenced by three parameters:• the range d(I~jp),• the reflectivity <strong>of</strong> the object, <strong>and</strong>• the angle<strong>of</strong> incidence.Figure 3.37 shows the development <strong>of</strong> the intensity relative to a maximum. The upper figure indicatesthe relation between the range <strong>and</strong> the intensity for different reflectivity values. The longer the range <strong>and</strong>the lower the reflectivity <strong>of</strong> the object, the less the intensity. The lower figure presents the intensity <strong>of</strong> atarget with a reflectivity <strong>of</strong> 90 % <strong>and</strong> shows that the intensity also decreases systematically. For example,the intensity line <strong>of</strong> the target with a reflectivity <strong>of</strong> 20 % corresponds to the intensity line to a target with areflectivity <strong>of</strong> 90 % <strong>and</strong> an anglevalues <strong>and</strong> low angles <strong>of</strong> incidence.<strong>of</strong> incidence <strong>of</strong> 30 °. Theintensity worsens with respect to low reflectivity
Change language