What is 3D mobile laser mapping and how does it work? What considerations need to be made when looking at the accuracy of a mobile mapping system? This presentation talks about mobile mapping systems and accuracy. If the accuracy of the data you want to capture is important to you, what do you need to look out for or ask about? If you would like more information about mobile mapping systems please get in touch - info@3dlasermapping.com or go to our website www.3dlasermapping.com/streetmapper

1. AN INTRODUCTION TO LASER SCANNING
PART 3 – MOBILE MAPPING AND
ACCURACY CHALLENGES

2. MOBILE MAPPING
• SURVEYING FROM A GROUND BASED MOVING VEHICLE
• COMBINING NAVIGATION DATA WITH LASER SCANNER DATA TO FORM A POINTCLOUD

3. 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

4. MMS COMPONENTS
• NAVIGATION
• INERTIAL NAVIGATION SYSTEM (INS)
• GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)
• DISTANCE MEASUREMENT INDICATOR (DMI)
• LASER SCANNER(S)
• CAMERA (OPTIONAL)
• MOUNT

5. 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

6. IMU ERROR OVER TIME – MEMS V FOG
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
0 50 100 150 200 250 300 350
3DError(m)
Time
MEMS 3D Positional Error over Time
30 60 120 180 240 300
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0 50 100 150 200 250 300 350
3DError(m)
Time
FOG 3D Positional Error over Time
30 60 120 180 240 300

7. 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

8. COLOURED POINTCLOUD

9. DO YOU WANT TO KNOW MORE ABOUT MOBILE
MAPPING?
IF SO, GO TO
WWW.3DLASERMAPPING.COM/STREETMAPPER
UK: +44 1949 838 004
South Africa: +27 12 940 0515
Australia: +61 (0) 8 9261 7703
North America: +1 720 214 3554