GeoVantage Displays Evolutionary Technology, Revolutionary
By Senior ANN Correspondent Kevin R.C. "Hognose" O'Brien
Take one airplane, four
Sony surveillance cameras, some cheap photographic filters, a large
helping of software wizardry made possible by Moore's Law, and
prepare over New England Yankee ingenuity as interpreted by a team
from all round the world. What do you get?
Precision georeferenced imagery -- in very near real time.
That's the promise of GeoVantage, Inc. of Swampscott, Mass, which
is delivering aerial photos that are extremely accurate and that
have location and terrain data embedded right in them, for the
benefit of customers in a variety of industries including forestry,
agriculture, urban planning and environmental management.
Aero-News was there at General Aviation Services at John
Mountain Field in Beverly, Mass, (KBVY), when GeoVantage held an
open house and demonstration of its advanced technology, on "GIS
Day": November 17, 2004.
GeoVantage's technology is evolutionary: they used COTS
(commercial off the shelf software), generic hardware, and common
electronic components to the maximum extent possible, and only
wrote their own stuff where it was needed to glue these disparate
pieces together. They also don't break new ground in the idea of
using overhead aerial imagery to examine things on the ground:
that's why the world's armies all got air-minded in 1914. But their
concept is revolutionary in several ways: in the way they have
automated the system, simplified the process, squeezed cost out and
-- most vitally
-- shortened the loop between the desire for imagery and the
delivery of accurate, precision imagery that can be used in
geographic information systems (GIS). Nobody ever had a really
good, really accurate system that can be flown in a light
single-engine plane and produce accurate imagery in near-real time.
Precision imagery, fast, has been the domain of massively
expensive, classified DOD programs -- not delivered via general
aviation to commercial end users.
The Airplane End
GeoVantage's Andy Lee was there with his yellow and white Cessna
Cardinal. Andy's Cardinal is fairly stock, except... except for the
small window in the bottom of the baggage compartment. It's an
STC'd camera window. But the camera in it is unlike any you have
Instead of one lens, it has four. "Regular Sony surveillance
Andy explains with a wry grin. New England Yankees still think
frugality is a virtue. Each lens has a filter on it: one is
near-infrared, the other three are Red, Blue, and Green. The
software will combine the images to provide color or IR images,
each of which has its uses. The four cameras are connected by
FireWire (IEEE 1393) to a hub, and into a computer that's placed in
the back seat of the Cardinal, running custom software on Windows
XP. A look at the camera with its sleek cover off reveals that it
is pretty much a breadboard project. Hey... is that duct tape?
"No," Andy deadpans. "We call that 'NASA Tape.'"
As anyone who's ever done aerial photography knows, a given
focal length at a given altitude will yield a specific scale. Most
GeoVantage missions are flown at 8000 ft. which produces a
resolution of one meter per pixel or 4000 feet, which produces
0.5m/pixel images, and other resolutions are available in similar
proportion. The resolution required depends on the intended use of
the images, balanced with the cost of the air mission -- naturally
you only cover half as wide a swath at the lower altitude/higher
resolution, so you have to fly more.
The camera is only part of the system, of course. Anyone can
take aerial imagery, and even scaled aerial imagery is pretty
straightforward. But the georeferencing is supplied by GPS.
Differential GPS is used, as in other very-high-precision
applications such as surveying; in DGPS a ground station at a
surveyed, fixed location receives and measures GPS deviations and
transmits corrections. This is the same principle (although not the
exact same technology) used in aviation's WAAS.
The GPS data not only records the information about the movement
of the plane, it compares it to a plot that was established during
preflight planning. To make a course plot, GeoVantage can use as
little as the GPS grids for the four corners of the intended image
area. Once coordinates for the area of interest are recorded,
GeoVantage establishes a course plot. The course plot establishes
the intended course, including turns and straight legs, that the
pilot must fly in order to achieve the necessary coverage. To
ensure complete coverage, there's a lot of overlap; only the 20% in
the center of each image that makes up the mosaic will be unique to
The course plot is part of the flight plan that is loaded into a
removable hard drive, and thence into the airplane. The pilot flies
the mission as plotted -- an indicator called the Steering Bar sits
atop the dash, and shows the pilot the extent that he has deviated
from the programmed course, almost like a localizer needle. If he
gets too far off the course, or gets out of the parameters for
which the software can correct the camera automagically shuts
At all times the computer unit in the aircraft is recording not
only the images but also the movement of the aircraft on its
removable hard drive. The GPS is only one source of data about the
aircraft movement -- an Inertial Measurement Unit or IMU also
tracks the plane's flight.
The resulting computer file contains differential GPS location
and speed information, but also data about the airplane's pitch,
yaw, and roll, sampled 125 times a second. This will be used to
correct for aircraft movement when the image is stitched and
All this capability is amazing, but Andy set it up in the
Cardinal in a few minutes: the equipment is all portable, and the
only modification to the aircraft is the camera window, commonly
done by STC or 337. The roomy Cardinal with its yawning doors makes
it easy to load, and to use, the system, but the lightweight,
portable system is easily adapted to any aircraft that has an STC'd
photo door or window. The greatest amount of the wizardry takes
place without direct human interaction.
The camera automatically turns itself on and off, and sets
exposure automatically. The challenge to the pilot is primarily to
fly the plotted course with the greatest possible precision and not
to exceed the parameters that would abort photography and require a
To Be Continued...