An Introduction to Laser Scanning - Part 3: Mobile mapping and accuracy challenges
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Transcript of An Introduction to Laser Scanning - Part 3: Mobile mapping and accuracy challenges
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AN INTRODUCTION TO LASER SCANNING
PART 3 – MOBILE MAPPING AND ACCURACY
CHALLENGES
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MOBILE MAPPING• SURVEYING FROM A GROUND BASED MOVING VEHICLE• COMBINING NAVIGATION DATA WITH LASER SCANNER DATA TO FORM A
POINTCLOUD
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WHY MOBILE MAPPING?• FAST
• QUICK TO MOBILISE AND MAP• LOWER OPERATING COSTS
• CHEAPER THAN CONVENTIONAL SURVEY• SAFE
• MINIMISES SURVEY STAFF ON THE HIGHWAY• HIGH RESOLUTION
• HIGH LEVEL OF DETAIL ON THE PAVEMENT AND STRUCTURES• FLEXIBLE
• CAN BE USED ON MANY DIFFERENT TYPES OF PROJECTS
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MMS COMPONENTS• NAVIGATION
• INERTIAL NAVIGATION SYSTEM (INS)• GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)• DISTANCE MEASUREMENT INDICATOR (DMI)
• LASER SCANNER(S)
• CAMERA (OPTIONAL)
• MOUNT
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MAINTAINING GOOD ACCURACY• UNLIKE AIRBORNE LIDAR, MOBILE MAPPING SYSTEMS SUFFER FROM LOSS OF GNSS
• WITH NO GNSS, TRAJECTORY ACCURACY DECREASES EXPONENTIALLY OVER TIME DUE TO IMU INACCURACIES• HIGHER GRADE IMUS WILL MINIMISE THESE ERRORS• FOG IMU MORE SUITABLE FOR CHALLENGING GNSS ENVIRONMENTS
• A DMI WILL HELP IMPROVE ACCURACY WHEN GNSS IS NOT AVAILABLE
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IMU ERROR OVER TIME – MEMS V FOG
0 50 100 150 200 250 300 3500.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
MEMS 3D Positional Error over Time30 60 120 180 240 300
Time
3D E
rror
(m)
0 50 100 150 200 250 300 3500.00
0.10
0.20
0.30
0.40
0.50
0.60
FOG 3D Positional Error over Time30 60 120 180 240 300
Time
3D E
rror
(m)
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INS COUPLING• COUPLING IS A TERM USED TO DESCRIBE HOW THE INS AND GNSS INTERACT WITH EACH
OTHER IN ORDER TO IMPROVE ACCURACY
• LOOSELY COUPLED• THE POSITION AND VELOCITY FROM THE INS AND GNSS ARE COMBINED TO FORM A
TRAJECTORY• ALL MMS’ WILL HAVE AT LEAST A LOOSELY COUPLED INS
• TIGHTLY COUPLED• ALSO COMBINES THE GNSS RAW MEASUREMENTS WITH THE INS, THEREFORE ALLOWING GNSS
POSITION UPDATES WITH FEWER THAN FOUR SATELLITES• DEEPLY COUPLED
• AS TIGHTLY COUPLED BUT INFORMATION IS ALSO PASSED FROM THE INS FILTER TO THE GNSS FILTER, WHICH ENABLES FASTER GNSS SIGNAL REACQUISITION
• DIA+• AS LOOSELY COUPLED BUT INFORMATION IS ALSO PASSED FROM THE INS FILTER TO THE GNSS
FILTER, WHICH ENABLES FASTER GNSS SIGNAL REACQUISITION
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COLOURED POINTCLOUD
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DO YOU WANT TO KNOW MORE ABOUT MOBILE MAPPING?
IF SO, GO TO WWW.3DLASERMAPPING.COM/STREETMAPPER
UK: +44 1949 838 004South Africa: +27 12 940 0515Australia: +61 (0) 8 9261 7703North America: +1 720 214 3554