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Mapping grade vs. survey grade
Managing expectations of mobile mapping systems
Dr Graham Hunter
Global 3D Laser Mapping Solutions
StreetMapper 3D Scanning Solutions LiteMapper & Terrasolid SiteMonitor for Mine Surveying
Innovative solutions
Over 12 years experience
Global technical support
What is a mobile mapping system?
Laser scanner Laser scanner
GPS antenna IMU
GPS/INS & Power supply
Control PC
Camera PC
Camera (one behind each scanner)
Mount StreetMapper offers flexibility in selecting mounts
StreetMapper 360 Mount
• Lifting platform
– Safety of staff + security + environmental protection
StreetMapper Portable Mount
Can be easily relocated around the world
What data does StreetMapper produce?
Coloured Point Data
Point Data + Images
CAD/GIS software Feature extraction software
Vector map/survey data Rapid 3D visualisation
Situational awareness (military intelligence)
Asset database
Mobile mapping quality
Survey grade vs. mapping grade
Survey grade 1cm
Mapping grade 100cm
High accuracy Low accuracy
High cost Low cost
Typical survey-grade specification
Error Budget (in order of importance)
1. Navigation – position
2. System calibration
3. Laser range noise
4. Navigation - attitude
Requirements for best accuracy
GNSS + Inertial Navigation
Post-processed GNSS
GNSS base station within 20km
Inertial aid to GNSS solution
Ground Control Points
IMU error with no GNSS
0
0.05
0.1
0.15
0.2
0.25
0.3
0 1 2 3 4 5
Deg
rees
Time (minutes)
SG_Gyro
SG_Drift
MG_Gyro
MG_Drift
Heading and elevation drift
2m
Elevation errors
What are the important issues?
GNSS visibility
- or what to do when GNSS is not visible
Mission planning – GPS visibility
Number of Satellites vs. time
INS Position RMS vs. time
• System estimation of positional error
INS Position RMS vs. time
• System estimation of positional error
Forwards and backwards processing
Direct Inertial Aiding I
Direct Inertial Aiding – No of satellites
Direct Inertial Aiding – Test site
Direct Inertial Aiding
GPS vs. GPS & GLONASS
GPS only
GPS & GLONASS
GPS vs. GPS & GLONASS
IMU Performance
INS solution based on
GPS only compared to
GPS/GLONASS
Calibration
Calibration
Before corrections, mismatch= 0.321m After corrections, mismatch= 0.007m
Before
After
GCP – Ground Control Point
Good Placement
Good Contrast
Strategy: Good GNSS: 1 every 500m Poor GNSS: 1 every 250m
Why use GCPs?
- To check accuracy - To improve accuracy
GCP – What can be used?
Existing Road Markings
Create your own GCP markings
GCP – To correct data
GCP in data
Use GCP to control the data
Average error before control = 3 cm Average error after control = 1 cm
TerraMatch can locate the targets in the pointcloud and correct for xyz
How to present system performance
City Model Accuracy Tests - Stuttgart
• Undertaken by Institute for Photogrammetry (ifp), Universität Stuttgart, Germany
• Compare to 3D model of City Surveying Office of Stuttgart
• 35 minutes surveying
• 18km survey
Navigation Accuracy
• Number of satellites along the route
• Estimated horizontal accuracy along the route
What can I do with a mapping grade system
Clearance / clash detection
Bridge Heights
• Plots lowest bridge height for each lane boundary
Asset Management
What can survey grade can do?
Survey Grade Mapping Grade
• Clearance / Clash detection • Bridge Heights • Asset Management • Railways (inc. Cuttings) • Tunnels • City Centres (Urban Canyon) • Race Track modelling • Highways (As built surveys)
• Clearance / Clash detection • Bridge Heights • Asset Management • Railways (inc. Cuttings)
Point Cloud to CAD
Key conclusion
• Understand your system performance in areas of poor GNSS
Thank You
Any questions?
3D Laser Mapping Ltd. Unit 1, Moorbridge Court
Moorbridge Road East
Bingham, Nottingham
NG13 8GG, UK
T: +44 (0) 870 442 9400
F: +44 (0) 870 121 4605
W: www.3dlasermapping.com
IGI mbH Langenauer Str. 46
57223 Kreuztal
Germany
T: +49 2732 5525-0
F: +49 2732 5525-25
W: www.igi-systems.com
