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Home   LiDAR News     

Marketing Accuracy … Under Control Print E-mail
Written by Cyn Rene' Whitfield   
Friday, 01 April 2011

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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