The Washington State Department of Natural Resources (WADNR) manages
more than 5.3 million acres of state-owned land for the people of
Washington. Of these, more than 3 million acres of trust lands were
received from the federal government at the time of statehood on Nov.
11, 1889. WADNR’s main goal is to provide leadership in creating a
sustainable future for the trusts and citizens of the state, and to
oversee development of state lands, with respect for natural resources
and the surrounding environment. It was natural, therefore, for the
department to exploit the benefits of digital photogrammetry.
Meeting the Challenge
Unlike many states, Washington has retained most of its trust lands to
provide a continuous flow of income to build public schools,
universities, community colleges, prisons, and state institutions such
as mental hospitals and the state’s Capitol building. With these trust
lands came the responsibility of managing them in perpetuity. As a
result, WADNR is always looking for better tools to help with its
resource management tasks.
Since the early 1970s, WADNR has been producing topographic maps, line
maps and orthophotos to record land changes and manage the state’s
natural resources more effectively. From 1973 to 1980, WADNR used
contract services for flying, ground control and orthophoto negative
production, with remaining work done in-house. In 1981, working with the
U.S. Geological Survey on a cooperative ortho project, WADNR acquired
its first aerial triangulation equipment and software. From 1981 to
1991, WADNR’s aerial triangulation process included manual searches for
established ground control using old U.S. Coast and Geodetic Survey (USCGS)
data, log book descriptions, and other state and county control when
available. WADNR also used analog point marking methods, measurement on
comparators and analytical plotters, and digital analytical block
adjustment—all of which took approximately two hours per photo to
complete.
In 1991, the manual search for ground control was supplemented with
expensive survey grade (centimeter accuracy) Global Positioning System
(GPS) equipment. Then in 1994 new, less expensive, hand-held,
resource-grade (sub-meter) GPS units were acquired to establish
coordinates on well-defined, photo-identifiable features. Therefore, it
was no longer necessary to search through old USCGS data for photo
control points. GPS yielded a solid, well-distributed, resource-grade
control net in the same amount of time or less.
Meanwhile, WADNR wanted to increase both
productivity and accuracy, and at the same time was moving to the
use of airborne GPS and, more recently, airborne inertial
measurement units. With the introduction of digital photogrammetric
methods, the agency soon reaped benefits such as automatic point
measurement, instant resetting of models to make additional
measurements, and digital orthophoto generation. Full digital
processing soon became the norm for most image processing and
resource data collection. By 1995, WADNR had acquired its first
digital photogrammetric workstation, running BAE Systems’ SOCET SET
software.
Digital Advantages
Before implementing digital photogrammetric workstations, WADNR
processed only 500 to 600 high-altitude black-and-white images per
year to generate hard-copy orthophotos. Now, using SOCET SET, with
its full digital image processing capabilities, WADNR has the
capacity to process more than 2,500 color images into digital color
ortho-photos annually, with approximately four times better
geometric accuracy. One of the benefits is that the higher
productivity enabled WADNR in 2000 to change from 1:63,360 to
1:32,000 photo scale to achieve better precision. To ensure that its
specifications are always met, WADNR prefers to use minimal ground
control to drift correct aerial triangulation block adjustments
rather than airborne GPS/IMU on its own. Typical triangulation rates
per image with SOCET SET are around 10 times faster than the
analog/analytical approach of the early 1990s.
“We have become significantly more efficient in our land-use
management practices because of advances in digital triangulation
processes,” says Dick Petermann, a WADNR photogrammetrist. “With 10
years of experience using digital triangulation, our technicians
utilize airborne GPS together with minimal ground control along with
larger photo scales to satisfy specifications. Triangulation times
per image are vastly improved. The results are used in our flowline
to generate digital orthophotos.”
WADNR was the first U.S. customer to use the SOCET for ArcGIS module
of SOCET SET, introduced in January 2005. WADNR technicians use
SOCET for ArcGIS to update the information in legacy shapefiles
annually. SOCET for ArcGIS is a SOCET SET module that adds a stereo
digitizing capability to all levels of ESRI Inc.’s ArcGIS software,
allowing 3-D information to be captured into 3-D shapefiles as well
as personal and enterprise geodatabases. Now foresters in the WADNR
photogrammetry group can complete additional tasks, such as forest
inventory and typing, allowing users with little or no
photogrammetry experience to maintain the extensive geodatabase more
efficiently, with increased accuracy and productivity.
Using software and equipment that costs one fourth of traditional
stereo plotters, WADNR has improved triangulation times per image
tenfold and geometric accuracy fourfold. The flexibility of using
digital images with SOCET for ArcGIS software also has increased the
use of aerial photography for GIS applications, forest resource
inventories, kelp beds and riparian monitoring, offering useful new
capabilities for WADNR to collect and update features in the ESRI
environment. Moreover, resource managers who have never used true
photogrammetric tools before find that they can use this new
technology to manage the state’s resources more effectively.
