Attending over 300 conferences in the past seven years, and talking to thousands of surveyors, a trend has become increasingly evident concerning the major players in the 3D world. I am not referring to the premier technology sharing conferences such as ILMF, SPAR and the ESRI User Conference as they are indeed cutting edge. The key players I refer to have a different acronym – PLS, Professional Land Surveyor. Not to diminish the role of the architect, engineer or scan technicians and manufacturers, what consistently comes to the forefront is in order to reach a certain level of accuracy it comes down to control, control, and control.
For mission planning, documentation, and data extraction obtaining a seamless, highly accurate deliverable is dependent on the spatial recognition applied by the surveyor to the project. Leica enhanced the value of control with the introduction of the fieldPro (AutoCAD plug in) in 2006. I have seen this product used as a powerful control tool in nuclear power plants and million square foot architectural projects. Riegl LMS VMX-250 compact mobile scanning solution sees success in its point calibration tools in RiProcess software.
The I-94 and I-696 interchange in Detroit, MI was collected on February 10, 2011. The temperature was 12⁰ F with a wind chill of 0⁰F, which made for a cold collect of some amazing mobile LiDAR data for Survey Solutions Inc. of Standish, MI using a new VMX-25. The project area consisted of a little over 3 miles scanned twice for complete coverage of the three lanes of traffic. The collection speed was 50 mph and the area had 12 overpasses along the length of the project, making for some difficult GPS sections in the real-time trajectory.
The raw LiDAR data was just under 4GB of data and the processed data is under 50 GB for all LAS and processed LiDAR files. The average to all control visible in the LiDAR is 0.210 ft unadjusted data and 0.01ft after adjustment.
Control Point
Raw Scan Elevation (ft)
Elevation (ft)
DZ RAW
DZ Adj.
100
462.539
462.356
0.184
0.020
101
SNOW
102
SNOW
103
470.233
470.052
0.180
0.023
104
471.798
471.647
0.151
0.007
105
470.935
470.781
0.154
0.003
106
469.219
469.012
0.207
0.043
107
466.827
466.673
0.154
-0.010
108
463.934
463.766
0.167
-0.003
109
462.234
462.083
0.151
-0.020
110
463.297
463.127
0.171
0.003
111
467.241
467.110
0.131
-0.010
112
470.322
470.108
0.213
0.075
113
472.037
471.854
0.184
0.016
114
473.652
473.451
0.200
0.010
115
474.764
474.478
0.285
0.069
116
470.233
470.013
0.220
0.026
117
464.314
464.091
0.223
-0.007
118
459.501
459.350
0.151
-0.016
119
462.835
462.621
0.213
0.007
120
468.888
468.688
0.200
0.000
121
472.523
472.297
0.226
0.020
122
474.078
473.885
0.194
-0.033
123
475.121
474.865
0.256
0.033
124
473.087
472.828
0.259
0.036
125
468.346
468.110
0.236
0.033
126
464.636
464.416
0.220
0.010
127
463.219
463.038
0.180
0.000
128
463.757
463.520
0.236
0.003
129
466.988
466.752
0.236
0.013
130
472.106
471.834
0.272
0.052
131
SNOW
132
482.546
482.362
0.184
-0.052
133
487.103
486.860
0.243
-0.020
134
490.531
490.272
0.259
-0.003
135
493.665
493.379
0.285
0.016
136
496.375
496.073
0.302
0.003
Average (ft)
0.210
0.010
Standard Deviation (ft)
0.044
0.026
Courtesy Riegl USA
Terrametrix, a 3D terrestrial mobile LiDAR scanning service provider uses TerraMatch which works inside Bentley’s MicroStation to achieve their survey grade accuracies. In fact, Terrametrix took testing of their accuracy to the extreme with it’s StreetMapper system at a CalTrans test area. The registered point cloud data was then compared to the 1500+ control points provided by Caltrans. An RMS error of 0.022’ was achieved.
Surveyor’s continually tell me that the mobile scanning technology is taking away their work. They are worried about the risk longevity of their profession. “You are replacing the surveyors.” Well, despite the arguments maybe… yes… in part when it comes to the scan world… but in a new revised way. True, accuracy with 3D laser scanning, whether static or TMLS, is dependent on control, but it is the spatial recognition and the ability to know how to place the control that is the key to the longevity of the profession in the 3D scan world. It is also the key to accuracy. Don’t let anyone tell you otherwise.
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For mission planning, documentation, and data extraction obtaining a seamless, highly accurate deliverable is dependent on the spatial recognition applied by the surveyor to the project. Leica enhanced the value of control with the introduction of the fieldPro (AutoCAD plug in) in 2006. I have seen this product used as a powerful control tool in nuclear power plants and million square foot architectural projects. Riegl LMS VMX-250 compact mobile scanning solution sees success in its point calibration tools in RiProcess software. 
