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Structure from Motion (SfM)

from K. Mankoff …A newish class of algorithms that have been classified under the name “structure from motion” or SfM. While these algorithms have been in use in the robotics / computer science / other domain for over a decade (Microsoft released an implementation titled “PhotoSynth” several years ago), they have not yet been widely used in the Earth Science domain. This is changing.

Three papers have come out in the past few months introducing SfM to Earth Scientists, providing case studies:

http://dx.doi.org/10.1002/esp.3366
http://dx.doi.org/10.1016/j.geomorph.2012.08.021
http://dx.doi.org/10.1029/2011JF002289

from Adam Steer …

1. It is possible to make 3D models using photographs using freely
available software (eg SfM toolkit, bundler, CMVS, PMVS), but packages
like Photoscan (mentioned by Matt) are vastly easier to use and
contain already the tools required to geolocate your point cloud, and
do some error analysis. I’ve built both an implementation of
bundler/CMVS/PMVS in Ubuntu Linux, attempted to install and run
SfMtoolkit in Windows 7, and managed to get my hands on Photoscan for
Linux. I don’t use bundler-> CMVS or SfMtoolkit anymore. One key
reason is that I can give photoscan apriori image coordinates for use
in its bundle adjustment, and get some ideas about predicted vs
adjusted camera positions (error). The other is that I don’t have to
chase *nix libraries for every new build.

2. On the down side, SfM algorithms struggle a little on ice, since
they rely on inhomogeneous imagery to work with. It is very easy to
make models of say, Antarctic stations. It is not very easy to make
great models of sea ice unless there are lots of features and the
light is good. Mountain glaciers or snowpacks on sunny days, however,
should provide great subjects!

jboxtimelapse1

EIS comes to Geografisk Institut, Københavns Universitet

During an invited lunchtime presentation, I will begin the process of assembling a team of students to analyze Greenland EIS data.

Title Extreme Ice Survey lapse cameras measure Greenland glacier changes

Abstract Beginning in 2007, the Extreme Ice Survey (EIS) installed 12 cameras beside 7 of the largest West Greenland glaciers. By 2009 EIS had captured extremely dynamic images that, especially when animated, teach us a tremendous amount ice-climate interaction and motion dynamics. In 2010, we published a scientific article[1] documenting a technique deriving glacier motion from single camera views. In this process, we developed and documented the software. By 2011, 3 new EIS rigs were installed by GEUS glaciology field workers at 3 new sites. Today, we stand ready to tap into the archive of photos, to apply our software and expand what we do. Let’s assemble a team of students to analyze the data with the help of Jason Box and James Balog. We’ve been only scratching the surface of the tip of the iceberg. Discoveries are within reach and include the possibility of more Greenland field work. We just have to take the next steps.

[1]  Ahn, Y. and J.E. Box, 2010: Glacier velocities from time lapse photos: technique development and first results from the Extreme Ice Survey (EIS) in Greenland, J. Glaciol., 56(198), 723-734. PDF