Surveying by motion tracking:
modelling 3D subterranean landscape
from video imagery
Anna Mason, David Mountain and Jonathan Raper
Study Areas
1. Requirements
3. Field Work
2. Equipment Tests
Conditions a caver might experience…
Dirty
Wet
Dark
Confined
Foggy
Camera Tracking and Line Surveying
Bullet camera
Line Survey
Records:
1.
Cave passage dimensions
2.
3D shape for vertical and
horizontal transects
3.
Reliable visual reference
Records:
1.
Absolute distance, bearing and
inclination
2.
Vertical and horizontal
dimensions
3.
Field sketches of shape
Camera tracking with 2D3’s Boujou4
Calculates optimal estimates of camera rotation and movement
in relation to objects as they are tracked throughout an
image sequence
Offers:
1. Automatic tracking or interactive tracking
2. Tracking with environmental markers or without
Cluster of 3D points on a marker
Data captured using bullet camera & Boujou4,
Chislehurst Caves
b)
2D view
a)
Bend caused by correction
of lens distortion
2D Feature Tracking
3D view
c)
User defined
coordinate
plane
Gap indicating a
passage junction
Camera tracking might not always be effective
Smooth curved surface
If there are few points for a corner
detection algorithm to detect
Could use:

Scene manipulation before
filming

Interactive feature tracking eg.
POIs, survey data, CAD model

Camera information

Colour correction of imagery –
not recommended, but may
make difficult imagery useable
How can you tell?

Spikes
Noisy camera path
Cameras in odd places
Not good


Virtual camera positions
do not reflect the real
world camera’s true
direction or path travelled
Noisy camera path
High reprojection errors
Camera tracking using Boujou4
c)
Start
point
First Frame
Last frame
Camera path
Camera path follows the direction and path the real
world camera travelled.
Camera path noise realistically reflects the terrain
3D Polyface Meshes
a) 3D view of a mesh in Boujou4.
b) The same mesh mapped to the
line survey results (red and blue
lines) in GIS.
3D modelling, Chislehurst Caves
Results


Upwood
Air Shaft
Highclere
Air Shaft

0
0.06
0.12
0.18
KM
© Crown Copyright Ordnance
Survey 2008
Mine passage connecting Upwood Shaft
to Highclere Shaft at Chislehurst, Bromley
Scale differences range
0.2cm to approximately
20.3cm.
Mean of four
measurements was
13.3cm.
Within 10-15% of the
exact measurements
suggested as acceptable
when sketching cave
passage shape (Day,
2002).
Cave survey sketches
Vs 3D meshes
Club Rooms,
Chislehurst
Air Shafts,
Chislehurst
Gaping Gill,
North Yorkshire
Field
Sketches
Vertical
Cross
Sections
Shallow half ellipse Arched ellipseTypical star shaped phreatic
cave morphology
Study Areas
1. Requirements
3. Field Work
2. Testing Equipment
Camera Tracking and Line Surveying
Line Survey
Bullet camera


Records 3D shape for vertical
and horizontal transects
Reliable visual reference

Records absolute distance,
bearing and inclination
measurements
Accurate representation of shape
Accurate measurement of dimensions /volume
Accurate measurement of relative scale
Benefits to GIS and Caving


New source of 3D data
Low cost accurate surveying
technique compatible with




GIS, CAD
Animation, AR, VR and
Visualisation software
Further Studies


Camera tracking research, eg.





Exploration rovers in
hostile environments
Robotic surgery
Navigation
Animation
Virtual TV

Comparison with laser ranging
and finding equipment
Compatibility with cave surveying
software
Test more equipment, eg.
infrared
Limitations
Image Quality
Camera lens and light must be
tailored to fit the scene:

References

6mm fixed lens and 6degrees
Scale must be defined by the user

Use h or d or a marker

Optimal camera moves create
parallax

Dolly rather than pan
Tracking corners

Begin/end with survey stations
Price ?

DAY, A.J., (2002) Cave Surveying – A
guide to the equipment, techniques and
methodology of the BCRA system, Cave
Studies Series No.11. Buxton, UK: British
Caving Research Association (BCRA)
DOBBERT, T. (2005) Matchmoving: The
invisible art of camera tracking, Sybex
Inc., Alameda, CA
HARTLEY, R. and ZISSERMAN, A. (2004)
Multiple View Geometry in Computer
Vision (Second Edition), Cambridge, UK:
Cambridge University Press
Acknowledgements
BCRA, 2D3, David Mountain and Jonathan Raper (City University), John Farrer
(Peak Cavern), Terry Hunt (Chislehurst Caves), Craven Potholing Club (Peak
Cavern), Adam Evans, Rod Legear, Paul Chambers
Thank you