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 12 F with a wind chill of 0F, 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 Bentleys MicroStation to achieve their survey grade accuracies. In fact, Terrametrix took testing of their accuracy to the extreme with its 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.
Surveyors 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. Dont let anyone tell you otherwise.