1. SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
‘Structure-from-Motion’: A high resolution, low cost photogrammetric tool for geoscience applications
Matt Westoby
Supervisors: Prof N F Glasser1, Prof J Brasington2, Prof M J Hambrey1, Prof J M Reynolds3
1Centre for Glaciology, IGES, Aberystwyth University
2University of Canterbury, Christchurch, NZ
3Reynolds International Ltd, Mold

2. ∘ Passive: stereo imagery ∘ Active: SAR, LiDAR Total station, TLS
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Introduction Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
• Traditional / contemporary methods for DTM/DEM generation:
∘ Passive: stereo imagery
∘ Active: SAR, LiDAR
Total station, TLS
• Often prohibitively expensive
• Portability issues in remote areas
Thus an identifiable need for an effective, portable and affordable alternative for obtaining high-resolution topographic data, at a range of scales.....
Aerial or spaceborne platforms
Ground-based

3. ‘Structure-from-Motion’ (SfM) photogrammetry
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example applications Comparison with TLS Discussion & summary
‘Structure-from-Motion’ (SfM) photogrammetry
‘Structure’ - structure to be reconstructed
‘Motion’ multiple camera baselines
Key problem addressed is the fully-automated estimation of camera pose, and determination of 3D location of matching features in multiple photographs, taken from different angles/perspectives, WITHOUT the need for manual control point identification.

4. SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example applications Comparison with TLS Discussion & summary
Popularised in past ~2-3 years through Microsoft’s web-based PhotoSynth application:
3D Panoramic
Sparse point cloud

5. Clustering views for MVS (CMVS) (Furukawa et al., 2010)
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example applications Comparison with TLS Discussion & summary
Key software / algorithms:
Scale Invariant Feature Transform (SIFT) (Lowe, 2004)
‘Bundler’ (Snavely, 2004) - sparse PC reconstruction
Clustering views for MVS (CMVS) (Furukawa et al., 2010)
Patch-based MVS (PMVS2) (Furukawa & Ponce, 2009)

6. Dig Tsho glacial lake / moraine dam complex
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
Dig Tsho glacial lake / moraine dam complex
Khumbu Himal

7. Dig Tsho glacial lake / moraine dam complex
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
Dig Tsho glacial lake / moraine dam complex
Photo: ICIMOD (2010)
Photo: TJ Peters (1982)
Photo: M. Westoby (2010)

8. GCP network established (35 yellow targets) - dGPS
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
GCP network established (35 yellow targets) - dGPS
1649 (ground-based) photographs taken across the moraine using consumer-grade camera (Panasonic DMC-G10) and used as input to Bundler, CMVS, and PMVS2
Bundler output (sparse point cloud) n = ,920
PMVS2 output (dense point cloud) n = 22,635,855
Transformation from relative to real-world (UTM) co-ordinate system performed by manual identification of GCPs in point cloud and shift-scale-rotate using centroid locations

9. SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary

10. Dam breach profiling A B A B C C Lake Flow
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
Dam breach profiling
SRTM
SfM A
Lake B A B C
Flow C
Image courtesy of GeoEye®

11. Quantification of moraine volume removed by outburst flood:
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
Quantification of moraine volume removed by outburst flood:
Post-flood geometry
Estimate of volume eroded by Vuichard and Zimmerman (1987) - ~900,000 m3
Estimate of volume eroded using SfM + DEM interpolation ,380 m3
Reconstructed

12. Estimate of water volume released (SfM) - >6.2 x 106 m3
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic principles Workflow Example application: Dig Tsho Comparison with TLS Discussion & summary
Post-flood shoreline
Pre-flood shoreline
Estimate of total volume of lake (Vuichard + Zimmerman, 1987) x 106 m3
Estimate of water volume released (SfM) >6.2 x 106 m3

13. Constitution Hill, Aberystwyth, UK
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
Constitution Hill, Aberystwyth, UK
Photograph
Sparse data
(Bundler)
Dense data
(PMVS2)
Photograph
SfM

14. SfM vs. TLS – Constitution Hill, Aberystwyth, UK
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
SfM vs. TLS – Constitution Hill, Aberystwyth, UK
TLS
SfM
11.5 x 106
points
11.3 x 106
points
TLS
SfM

15. SfM vs. TLS – Constitution Hill, Aberystwyth, UK
SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
SfM vs. TLS – Constitution Hill, Aberystwyth, UK
92,500
Aerial photograph
Point density (m2)

16. SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
zdiff (m)

17. SfM: a high resolution, low cost photogrammetric tool for geoscience applications AGU Fall Meeting 2011
Overview Basic Principles Workflow Example applications Comparison with TLS Discussion & summary
Discussion / Summary
∘ Operates under same basic principles as stereoscopic photogrammetry, though multiple photos (1000+) used as input
∘ Software/algorithms freely available – no need for expensive photogrammetry packages (+training)
∘ Extremely portable – consumer-grade digital camera, GPS, and GCP targets
…thus well suited for rapid, high-resolution micro- and meso-scale terrain reconstruction in remote areas – e.g. moraines, debris-covered glacier surfaces
∘ Comparison with TLS data reveals minimal differences across majority of test site
∘ Main disadvantage – struggles with homogeneous terrain – e.g. snow, grass, sand
∘ Flexibility – ground-based data collection presented, though photo acquisition from low-altitude aerial platforms (UAVs, blimps, kites) far more effective for covering large areas – e.g. Debris-covered glacier surface, floodplains
Thank you.
Acknowledgements:
Field assistance:
John Balfour
Pippa Cowley
Sam Doyle
James Hickman
Heidi Sevestre
Mark Smith
Colin Souness
Summit Trekking Ltd, Kathmandu
Financial support:
NERC Open CASE Award
Aberystywth University
Reynolds International Ltd.