January 2012
Clemson University, Duncan-Parnell and Trimble’s Most
Advanced Technologies Are Helping Preserve Historic Fort Sumter
More than 180 years after its construction, and 150
years after the famous shot that started the U.S. Civil
War, Fort Sumter is once again at the forefront of a
battle. This time around, the enemy is nature, and the
loyal troops defending the fort aren’t depending on
cannons and masonry walls. Instead, they’re relying
on highly-sophisticated 3-D scanning and surveying
technologies from Trimble and Duncan-Parnell, as well as
decades of experience and extensive data processing.
The “soldiers” in this battle are surveying professionals
from Clemson University, and their mission is to help
preserve one of America’s most significant historic landmarks. The methodology they have chosen for this effort
may ultimately establish a new standard for monitoring
sensitive historic and archeological sites.
A storied history.
Sitting on a man-made island of granite and sea shells at the
mouth of the Charleston, SC harbor, Fort Sumter originally had
walls 8 to 12 feet thick and 50 feet high. On April 12, 1861,
Confederate batteries fired on the fort from the surrounding
shorelines. The next day, the Union garrison occupying the fort surrendered, and the U.S. Civil War was underway. Later, in August
1863, a Federal bombardment began that ultimately reduced the
massive walls to rubble. By the time the war ended, Fort Sumter
was in ruins.
In 1898 the Spanish-American War produced a renewed interest
in the site, and a huge concrete battery was constructed in the
center of the old fort, where it remains today. During World War
I a small garrison manned the battery’s two twelve-inch rifles, and
during World War II, two antiaircraft guns were installed, although by then the fort was primarily a tourist attraction. In 1948,
Fort Sumter became a U.S. National Monument administered by
the U.S. National Park Service.
A national treasure threatened.
Because of its location and construction, Fort Sumter National
Monument is subject to many natural destructive forces. The island
is known to be slowly sinking, and the fort’s walls now sit barely
above sea level during high tide. The fort’s northern flank faces
the Port of Charleston’s main shipping channel, where frequent
traffic generates moderate wave action. The tides and wind also
work together to keep much of the exterior wall surface perpetually
damp. For historians, archeologists and preservationists alike,
these threats to Fort Sumter are serious matters.
To better understand the situation, in 2011 a multi-year project
was launched with the goal of assessing the structural integrity
of the fort, instituting a structural health monitoring program, and
accurately measuring the fort in order to establish a benchmark for
future comparisons. If measurements in subsequent years were to
show that the fort is deteriorating too rapidly, additional preservation measures could be considered before it’s too late.
Measuring tasks for the project are being led by Clemson
University’s Peter Messier, with support from a graduate student
and three former students who are now licensed practitioners,
and several of the university’s departments. Scanning and survey
instruments are all products from Trimble Navigation, Ltd., while
scanning assistance and comprehensive support is being provided
by Duncan-Parnell. (continued on next page...)
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Y O UR T R I MBL E SURV EY C O N N E C TIO N
I N THE CAROL INAS AND G E O R GIA
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the fort’s components over time. Stainless-steel threaded rods
were permanently installed for the wall monitoring points. When
measurements are conducted, custom-built targets are mounted
on each rod. For protection, these rods are topped with stainlesssteel acorn nuts when not in use.
Other preparation work included taking core samples from a
handful of gun casements. By determining the exact make-up of
the wall material, the team will be better able to predict movement once the 3-D model is completed in the months ahead.
Project scope.
From the start, the challenge was daunting: how to measure
every aspect of a 180-year-old fort (on a man-made island in an
active harbor), to determine whether it is moving from one year
to the next, all with millimeter-level accuracy. In the summer of
2011, the project team developed an ambitious plan that would
include:
• Establishing control and monitoring points
• Conducting numerous precise measurements
• High-resolution 3-D scanning of the entire fort
• 3-D modeling of six gun casements
Peter and his students would be responsible for establishing all
control/monitoring points, conducting all measurements and
many other details. Duncan-Parnell’s Dan Bonenfant would be
responsible overseeing the scanning operation and processing
data. And additional Clemson engineering resources would
develop the 3-D model.
Preparation work.
With a plan in place, the team started by locating SC State
Plane Coordinates to determine an absolute position for Fort
Sumter. Static GPS measurements were taken on two different
days at different times to help ensure accuracy. Five primary
control points were established, including three on the surrounding shorelines and two on the fort itself. These will provide a
basis for monitoring long-term movement of the island, and allow
the team to isolate the fort’s control points from the island.
In order to determine absolute elevation over
time, a deep benchmark was established
outside the fort’s walls by the South Carolina
Geodetic Survey. A stainless steel rod was
driven to refusal (approximately 70’), making
it independent of any vertical movement of
the fort or island. So even if the island exhibits
sinking, the rod will remain at the same elevation.
In order to track any movement of the
fort, 96 permanent monitoring points
were established along the top of
the walls and inside some of the gun
casements. These will provide precise
definition and stability for measuring
Y O UR T R I MBL E SURV EY C O N N E C TIO N
I N THE CAROL INAS AND G E O R GIA
The measuring process commences.
As summer drew to a close, baseline measurements of Fort
Sumter began. The team started by running a 3-D traverse
circuit along and very near the outside perimeter of the fort, and
another through the fort’s interior. Moving forward, this would
provide both horizontal and vertical control for terrestrial scanning
stations, and tie all scanning into one unified coordinate system.
Due to a desired accuracy tolerance of +/- 1 to 2 millimeters,
this process was very time consuming to set up and measure.
Next up was one of the more challenging aspects of the project:
scanning the fort’s northern and northeastern exterior walls. These
walls are particularly difficult to scan due to the large boulders at
the base of the walls, and a 3 to 4 hour window of opportunity
for scanning centered around low tide. At high tide, the area
is inaccessible, and at all times, it is dangerous work. The
team relied on rock climbing gear for protection, with spotting
provided overhead from the top of the fort’s walls.
A Trimble® CX™ 3D Scanner was
used to scan sections of the walls at
extremely high resolutions. During
post-processing, these scans will be
overlaid to create what amounts to a
seamless image of the fort. Although
lower resolution scans may have
been suitable for 3-D modeling purposes, the higher-res scans
will provide comprehensive data for future analyses. They also
provide an astonishing amount of surface detail, down to tiny
cracks in individual bricks. This same scanning approach was
employed inside the fort as the gun casements were scanned.
With the approach of Thanksgiving and winter weather, the team
shifted its focus to the remaining two primary measuring exercises
for the project:
• Precise level circuit to the wall monitoring points
• Precise radial survey to the same points
Both of these measuring procedures were conducting using the
industry’s most advanced robotic total station, the Trimble S8,
and the Trimble DiNi® precise digital level with invar staff.
The level circuit provides precise elevations for each of the
monitoring points that were installed along the top of the fort’s
walls. When compared to the results of future measurements, it
will be possible to determine if the fort is experiencing any vertical structural deformation over time. The level circuit originated
at, and closed back to, the deep benchmark buried earlier. It
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It’s Winter Tune-Up Time!
required multiple runs due to various constraints, as well as data
reduction, analysis and computations.
The radial survey provides a method of analyzing any horizontal
structural deformation of the walls over time. Precise horizontal
positions (x, y) were determined based on back-sights to the three
precise shore points located 1.1 to 1.3 miles away. Because
of obstructions, two eccentric observation stations on the roof of
the battery were required. Special procedures, data reduction,
analysis and computations were also required.
The team presses on.
The Fort Sumter measuring and monitoring project is well
underway, but there is still much to be done. As of this writing,
the initial round of monitoring measurements have been taken,
and a sizeable number of 3-D scans have been captured. Still
ahead lie the remaining scans, data processing, development
of the 3-D model, and more. Additional progress reports will be
published on a regular basis. For the latest updates and more
photos of the project, visit http://blog.duncan-parnell.com/.
Has it been a while since your last “Clean and
Calibrate”? If so, it's time to take your instrument
to the nearest Duncan-Parnell location to have it
tuned-up before the season gets started in earnest.
Or if you prefer, you can ship your equipment
directly to one of our service centers listed below.
Before shipping, please make sure your device is
packed properly and insured.
Our Winter Tune-up includes all adjustments to
bring your equipment back to factory specs:
• Inspection of the device
• Calibration & complete cleaning
• Firmware & software checks 1
• Internal battery inspection and replacement
if required 2
• New Screen protector where applicable
Charlotte Service Center
Survey, Construction, Mapping & Layout Equipment
For Estimates Call:
Blain Vanderhoof, 1-800-849-7708
Shipping Address:
Duncan-Parnell Service Dept.
900 South McDowell Street, Charlotte, NC 28204
Morrisville (RTP) Service Center
Mapping Equipment
For Estimates Call:
Scott Stephenson, 1-800-353-7392
Shipping Address:
Duncan-Parnell Service Dept.
1208 Copeland Oaks Dr., Morrisville, NC 27560
1
Above: a composite image created by combining
multiple scans of several gun casements
Toll Free: 1-800-353-7392
2
Additional charges may apply if a software/firmware upgrade
is required/requested for the device and is billable by the
manufacturer.
Additional charges for parts may apply and will be included in
the estimate.
duncan-parnell.com
January 2012
In This Issue
• Special Feature Article:
Clemson University,
Duncan-Parnell and
Trimble’s Most Advanced
Technologies Are
Helping Preserve
Historic Fort Sumter
• Winter Tune-Up Time for Surveying Equipment
YOUR TRIMBLE SURVEY CONNECTION
IN THE CAROLINAS AND GEORGIA
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Special feature article inside: Clemson University,
Duncan-Parnell and Trimble’s Most Advanced
Technologies Are Helping Preserve Fort Sumter.
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