Transcript Document

RIMM-CAPP
(Ripple Mark Mapping – Camas Prairie Project)
Katie Roskilly, Ed Kleinsasser, Fred Bunt
Sean Lodmell
Dept. of Physics and Astronomy, University of Montana
Hellgate High School, Missoula, MT
Introduction
Image Processing Methods
The focus of this project is on the integration of a threedimensional camera system and a tethered balloon to attain
stereoscopic photographs of the prominent glacial ripple marks in
Camas Prairie Montana. Salish Kootenai College has collaborated
with and has been instrumental in securing land permissions
needed for the project.
Our objective
with the UM-BOREALIS tethered balloon is to create a three
dimensional image for a digital elevation model (DEM) of these
ripple marks left over from Glacial Lake Missoula. In 2011
stereoscopic images were taken in the area, but at too low
resolution and did not achieve the desired geospatial accuracy
and precision of ±.5 feet.
Mapping
these ripples will provide useful and new data to geologists
reconstructing past global scenarios as well as interdisciplinary
scientists modeling fluid flow. Furthermore, as our imaging
capabilities stretch further into space the use of digital elevation
models (DEM) as a comparison model to the mapping of other
planets, particularly Mars, has become a necessity.
This
poster will outline previous work done on the project and future
enhancements to be initiated this summer.
Two main software programs will be used to process the images from the
camera system, Photosynth and ArcGIS.
Imaging Methods
The camera system consists of two Casio EX-H20G, 14.1
megapixel cameras mounted to a tethered balloon. A converging
axis will be implemented to obtain low post-production three
dimensional images.
A circuit will be wired to both cameras to allow remote
shutter to ensure proper image capture timing. Remote image
monitoring will be implemented to ensure the proper range of
photographs are taken on every flight.
The camera system will be leveled using a Picavet
suspension equipped with PeKaBe ball-bearing blocks. The
suspension consists of a rigid cross suspended below the balloon
from two points. A single line will be threaded several times
through eye-hooks connected to pulleys allowing the weight of the
rig to settle naturally to a level position.
The two cameras will take images at 60% overlay. To get a
map scale of 1 inch: 600 feet, with a camera of focal length 24240mm, the tether would have to be about 40 feet above ground
level.
We will us at least 9 ground control points, GCPs, in our field
of view. To calculate field of view we use optical formulas. For
these we need image size, d, and this could be defined by the a
flat panel screen we use to identify GCPs in the image, as well as
angle of view from the camera lens (see Image Processing
Methods).
The size of individual GCPs will be 6X8 foot tarps to create
a 3X3 grid and have 40 foot spacing between GCPs. The GCPs
must also be contrasting colors in order to be seen in the later
generated point cloud. The GCPs will be used to assist in bringing
our arbitrary coordinate grid, generated by Photosynth, into real
world coordinates.
•Photosynth: Photosynth uses an algorithm to remove photos it determines as
outliers, chooses points of interest in photos and match them to the same
points on other photos, and creates a 3D point cloud. A point cloud is simply a
set of vertices in space that represent the surface of a desired object. An
arbitrary coordinate grid will be assigned to ground control points in the
overlaid images. This process requires about 800 photos. This number of
photos is required by Photosynth to find matching features in at least
three separate photos taken from different locations and to limit angles
between photos, about one photo every 25 degrees, to make the synth work
better.
.
•ArcGIS: Once the 3D point cloud is generated from the overlay, the points are
put into ArcGIS. This program transforms our point cloud into real world
coordinates and creates our DEM. This system will be replicable at a fairly lowcost, minimal production level, lending to the possibility of use by other learning
institutions or scientific facilities.
Figure 1: Tethered balloon photographed from
ground.
Figure 3: Point cloud overlaid on Bing map of area.
Figure 4: Photosynth point cloud from August 2011 launch.
Acknowledgments
Figure 2: DEM above from point cloud displayed
to the right.. Pink is a lower elevation than green.
Approximate location of this area is 47.5365
latitude and -114.607 longitude with an average
elevation of about 3000 feet. The DEM is
currently displaying an arbitrary coordinate
system and should be projected to a known
coordinate system for mapping purposes.
Jennifer Fowler, University of Montana, Flight Director UM-BOREALIS
Mindy Mason, BLM Geologist
Dr. Marc Hendrix, University of Montana Geosciences Department
Jill King, Project Videographer
Jim Sheldon, Ice Age Floods Institute ,Lake Missoula Chapter President