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Digital Close-Range Stereophotogrammetry for Heritage Recording The Impact of Responsible Measurement

May 15, 2004

PREFACE
The loss of or damage to an object’s fabric, whether
from benign neglect or catastrophic events, is always
unfortunate. But all too often it is a finality – especially if
no accurate records exist of the object prior to its damage
or destruction. If, on the other hand, a structure had
been previously recorded using the principles of digital
close-range stereophotogrammetry, that structure could
be restored with unparalleled accuracy and precision at
any time in the future.
The benefits of recording with digital close-range
stereophotogrammetry are the result of replacing field
measurements with image measurements. This removes
the need to physically access each point at which a measurement
is required. In short, if one can see it, the exact
location can be determined from the photography. The
major benefits are:
BY PETER BELDEN TRIEB
AND DON KILPATRICK
ABSTRACT
Heritage buildings are often the sole providers of specific historical
knowledge unavailable elsewhere. Responsible treatments to these
structures can be achieved only through a thorough understanding of
their history and construction, allowing future generations to be stewards
to their present-day care. Buildings are recorded to interpret,
understand, and explain their history, construction, evolution, and decoration.
These irreplaceable members of our built environment need to
be recorded before any work takes place – particularly the development
of any conceptual treatments or specifications. This paper will discuss
the methods and advantages of using digital close-range stereophotogrammetry
for heritage building recording and data collection.
Respecting and caring for our true clients – our built heritage – in a way
that sensitively addresses the goals and needs of the building’s owners
and caretakers will provide the stewards of our architectural heritage
an even more effective means to record the present, understand the
past, and plan for the future.
NO V E M B E R / D E C E M B E R 2004 I N T E R FA C E • 1 3
DIGITAL CLOSE-RANGE
STEREOPHOTOGRAMMETRY
FOR HERITAGE
RECORDING
THE IMPACT
OF RESPONSIBLE
MEASUREMENT
• Permanent archival record.
Stereophotography is an extremely
valuable archival resource in its own
right. It provides much more information
than conventional pictorial
photography and leaves open the
possibility for future assessment.
The photographs may be used either
for monitoring or for the generation
of data. In addition to the future
production of line drawings, rectified
photography,1 orthophotography,2
and solid models,3 photogrammetry
also provides a photographic (and
very often stereoscopic) documentation
of objects. Properly cared for,
these photographs are the permanent
archival building record for
future generations.
• Noncontact and nonintrusive
method. The method is generally
much safer than methods of hand
survey, owing to its noncontact
nature. It is essentially a form of
remote sensing and is akin to
Nondestructive Testing4 (NDT) as
widely recognized in the architectural
conservation field. Noncontact
measurement is very often desirable
with archaeological objects; for
example, cave paintings, delicate
artifacts, mummies, and so forth.
• Cost effectiveness. This benefit, of
course, depends on the requirements
of the conservation project in
general, and the parameters of the
recording process in particular. But
for detailed work, this method is
usually very competitive against
others. For highly complex structures,
it is the most economic means
of recording, because the field survey
and photography only need to be
done once and the analysis and plotting
can be performed whenever and
to whatever extent the client and
conservator deem appropriate. In
that way, many important architectural
and archaeological objects can
be documented on-site in a short
time and with little expense.
• Reduced field times. Field operations
are reduced to the image
acquisition and the geodetic survey
of a few control points. The main
work may be done at any time and
any place independent of the building
or object, because the geometry
of the object is stored in the images.
Photogrammetry now allows measurements
previously taken in the
field to be done off-site, limiting any
potential interference with daily
building operations and also resulting
in safer documentation procedures.
• Complex objects. The technique is
ideal for recording very high levels of
detail and interpretation of the detail
is made easier because of the threedimensional
view. Extensive intricacies
in the structure’s detailing only
necessitate more image analysis and
plotting time off site. One of the
main powers of the technique is its
flexibility. It can handle objects of
virtually any size, and it does not
require the recording positions of
the cameras to be known.
• Selective analysis. The level of
detail to be extracted may be determined
either by the client or the
photogrammetrist. The quality of
conventional recording very often
14 • I N T E R FA C E NO V E M B E R / D E C E M B E R 2004
Figure 1: Stereopair of south elevation of Rockefeller Chapter at the University of Chicago.
(Photo by Peter Belden Trieb.)
depends on the qualifications, interest,
or opinion of the documenting
conservation professional. The photograph
is objective since everything
is recorded automatically. Especially
at rescue excavations, layers of
shards or stones can be very
painstaking to document.
Photogrammetry can accelerate the
recording procedure by delaying this
detailed analysis until after completion
of the fieldwork.
Digital close-range stereophotogrammetry
is a proven and precise recording technology
that addresses the intricacies and
inaccessibility of many heritage structures.
The technology involves taking two overlapping
photographs and importing the resulting
stereopair5 (Figure 1) into a suitable
computer to produce a digital stereo image
that can be manipulated in all three (X, Y,
and Z) dimensions. Although various
recording technologies use the common
term “photogrammetry,” only stereophotogrammetry
can allow true three-dimensional
(3-D) reproduction of real-world
objects through the manipulation of an
image of that object.
Digital close-range stereophotogrammetry
is also the only accurate method of
recording 3-D information about an object
that results as well in an archival, high-resolution
photographic base record of the
object.
Because the in-office data collection
phase (plotting and drawing) can be the
most expensive aspect of digital closerange
stereophotogrammetry, limiting
the recording project to the acquisition of
the field data only (photography and survey
control points) will allow more buildings
to be documented for a given expenditure
while retaining the capability to
produce measured drawings and 3-D
data. This is what is meant by responsible
measurement.
Definitions
Photogrammetry is the art, science,
and technology of obtaining reliable twodimensional
(2-D) or 3-D information
about physical objects through the
processes of recording, measuring, and
interpreting photographs. The position,
size, and shape of an object can be determined
by measuring its image rather
than directly. An important feature is the
fact that objects can be measured without
being touched. Principally, photogrammetry
can be divided into aerial photogrammetry
(camera principal distance set
to infinity) and close-range or terrestrial
photogrammetry (camera distances set to
finite values).
Stereophotogrammetry is the general
term applied to the science of measurement
from photographs when an overlapping
stereopair of photographs is used. In contrast
to single photographs, which can
extract only 2-D information, stereophotogrammetry
allows 3-D information to be
extracted. Stereophotogrammetry, using
either film photography or digital images, is
the basic tool used to produce 99 percent of
all maps of the Earth that show 3-D information
(planimetric detail plus contours or
spot heights).
Close-range stereophotogrammetry is
used to describe the technique when the
object to be measured is less than about
100 meters from the camera.
Survey control
The first step in any photogrammetric
project is to collect data in the field. This
involves establishing a network of control
points to establish a reference system
between the photographs and the real
world, as well as taking the actual photographs
of the project area.
In the first years of modern architectural
photogrammetry, control data collection
using optical/mechanical theodolites6 was
time consuming and laborious, requiring
extensive booking and checking procedures.
The electronic total station (Figure 2)
has speeded up this process enormously by
digitally logging the observations and
increasing their reliability. The total station
is a precision survey tool frequently used for
many geodetic surveying projects. It measures
slope distance, horizontal angle, and
vertical angle. Survey software computes
the 3-D coordinate values and adjusts for
any observational errors. Data precision to
1-2 millimeters is only obtained through
using appropriate surveying procedures.
Photography
For stereophotography, each feature of
an object has to be displayed on at least two
images from different points of view. If one
wants to view stereoscopically, the images
should be taken according to the normal
case of photogrammetry with near parallel
directions of view from two points on a horizontal
base, as is the case with the human
eye.
NO V E M B E R / D E C E M B E R 2004 I N T E R FA C E • 1 5
Figure 2: A modern survey total
station. (Photo by Peter Belden Trieb.)
Figure 3: Photogrammetric roof plot at Chateau sur Mer, Preservation
Society of Newport County, Newport, RI. (Photo by Peter Belden Trieb.)
The scale of a photograph is simply a
function of the distance to the object from
the camera and the principal distance of the
lens. For example, if the subject is 10
meters away and the lens is 100 millimeters
(0.1 meters), the scale of the photograph is
1:100. It is essential to have good prior
knowledge of the available on-site distances
since there may be obstructions such as
trees, shrubbery, or narrow streets. The
quality and precision of the survey depends
on the scale of the imagery, and one can
expect 1-2 millimeter precision from 1:100
scale photography.
For architectural purposes, the overlap
between two successive images is usually
about 70 percent. This is greater than the
aerial case, but helps to make stereoviewing
easier for the inexperienced, and the precision
requirement in the Z direction (depth),
although reduced compared with X and Y,
is usually more than sufficient.
Photogrammetric line
drawings
The most commonly applied photogrammetric
product continues to be the
line drawing, produced from stereophotography
on a photogrammetric plotter (Figure
3). Typically, such line drawings are at 1:20
or 1:50 scale and usually show all architectural
detail and stonework jointing.
Drawings produced at 1:100 scale are rare,
perhaps reflecting the fact that the valuable
attributes of accuracy and detail to be
obtained through photogrammetry are not
so evident at this scale. Drawings at 1:10 or
even 1:5 scale tend to be of selected highly
detailed sections only. However, a trend
since about 1985 has been the drift to the
larger scales of production, 1:20 now being
regularly specified. The photography for
such a survey continues to be taken for the
most part with metric cameras, such as the
Wild (now Leica) P31 (Figure 4), Wild P32,
and the Zeiss UMK 10/1318.
Virtually all photogrammetric data are
now output digitally. This allows change of
scale and layering of data, thus making the
final output much more flexible. Now 3-D
data are commonplace, allowing all details
of the stereo-model to be faithfully and
carefully traced (Figure 5). As more use is
made of three-dimensional CAD programs,
data capture in this way has become essential.
The stereophotographic
record
Photography for photogrammetry has a
great value in its own right. Not solely a
means to an end, heritage photography as a
record is of great significance and should be
recognized as such. Generally, all photography
taken for photogrammetric purposes
should be carefully preserved. In some
areas, stereophotography may be especially
useful and appropriate. As a record of
stonework condition, stereopairs at very
large 1:10 to 1:20 negative scale have
proven to be tremendously valuable. The
stereophotography can reveal a wealth of
information concerning the surface of the
stone and can be repeated at scheduled
intervals, providing an objective and periodic
record of condition.
Three-dimensional
modeling
For enhanced presentation and analysis,
the photogrammetric data are easily
manipulated into 3-D models that can then
be rendered either with standard palettes of
materials (Figure 6) or more realistically
with the images themselves. Once in a 3-D
dataset, horizontal and vertical cross sections
can be produced automatically anywhere
in the model.
Figure 5: 3-D CAD linework accurately created from
digital stereo imagery.
16 • I N T E R FA C E NO V E M B E R / D E C E M B E R 2004
Figure 6: Stained glass window. Full, 3-D
modeling of the window stone tracery
was produced to assist the architect and
masons in its reconstruction.
Figure 4: Wild P31 100mm metric survey
camera in use. (Photo by Peter Belden Trieb.)
Photogrammetry – why
and when?
• Understanding. The interpretative
value of photography as one of a set
of tools for the architect, engineer,
archaeologist, and conservator is
almost unsurpassed. And one can
add to that the greater quality of
large-format survey photography
and the value of stereoviewing.
• Intervention. The presence of a
base record for any work on a project
would be very valuable, and if
any intervention is likely to cause
problems for the fabric (e.g., dust,
damage, movement, subsidence),
the base photographic record can be
consulted, especially if any legal
argument arises.
• Archival purposes. Increasingly
being considered is the establishment
of an archive of photography of
an important building or monument.
This would be helpful even if
the photography were nonmetric
and nonstereo, but it would obviously
be beneficial to any future
study of the design, materials, or
condition if the photography were
metric and stereo. In 1978, the
entire exterior of Trinity College,
Dublin (Fig. 7), was photographed in
stereo for archival purposes, which
proved useful when restoration work
was required 12 years later.
• Disaster preparedness. This can
take the same form as an archive,
but is often considered when there
is a likelihood of some sort of disaster
affecting the monument (e.g.,
flooding, fire, earthquakes, hurricanes,
or volcanic eruptions). Costs
can now be justified.
Benefits
• Permanent, reusable archival
images. The photographs serve as
an archive describing the state of
the object at the time of the recording.
Because the images can be
saved in a digital format, new measurements
can be added at any time
without having to remeasure the
object. One simply uses the photographs
recorded in a previous session
to perform some additional
measurements. Furthermore, the
images always provide a good
overview of the situation at the time
of recording, which provides the
opportunity to reconstruct a situation
from the past when necessary.
An analysis can be done when
desired (for example, if the object is
destroyed and should be rebuilt).
• Cost effectiveness. Close-range
photogrammetry is generally less
expensive than any other method of
measuring. The cost effectiveness of
the system increases with the
amount of details and the complexity
of the object and with the accuracy
requested. Using photogrammetry,
the known cost effectiveness of 3-D
CAD can be practically applied to
rebuild projects. Ironically, the more
detail the site has, the easier it is to
survey with photogrammetry and
the more cost effective it is. Return
visits to pick up missed detail are
reduced.
• High accuracy and precision. The
accuracy of photogrammetric analysis
is, in almost all cases, better
than other commonly used methods.
Feature identification and accuracy
to millimeter (and even submillimeter)
tolerances are easily achievable,
depending on the initial design
requirements of the recording
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18 • I N T E R FA C E NO V E M B E R / D E C E M B E R 2004
process. The accuracy of the photogrammetric
recording can be calculated
in advance and targeted to
the purpose of the survey.
Photogrammetry picks up a level of
detail that cannot be obtained
through any other surveying technique.
Even if low-cost systems and
amateur (calibrated) cameras are
used, the errors will be comparable
with those produced by conventional
recording techniques.
• Direct capture of 3-D digital data.
The direct production of 3-D data is
ideal for input to CAD systems, and
the use of digital data ensures total
flexibility, an increasingly important
need in the CAD era. Drawing production
is fast, accurate, and easy
because pictures of the object are
always available to identify features
accurately and completely.
Conventional measurement techniques
would require the additional
step of inputting data into a CAD
system. With photogrammetry, the
data are already in a CAD format,
thus eliminating a great deal of engineering
cost and scheduling time.
• Reduced field times. Actual recording
time is very short compared with
more traditional measurement
methods. The object to be recorded
is fully available once the photographs
have been taken. Data is
later extracted from the photographs,
eliminating site visits to
collect additional information. In
addition, because this type of data
collection is much faster than traditional
surveys, it limits the exposure
of personnel to hazardous areas
(extreme temperature, toxic materials,
radioactivity, and so forth).
Photogrammetry is also very suitable
in areas where measurement
requires an actual facilities shutdown,
allowing the process downtime
to be minimized, further reducing
costs.
• Restoration and reconstruction. If
the building is destroyed or damaged
and images are available, photogrammetry
can provide sufficient
data for reconstruction. At excavations,
features from upper layers
have to be destroyed when digging
down to the lower layers. If later on
the documentation turns out to be
insufficient or incorrect, the information
is irretrievably lost. However, if
the features were recorded in a way
that is suitable for photogrammetric
analysis, the documentation
can be checked, verified,
or corrected at any time
later on. This is extremely
desirable, especially when the
results have to be analyzed by
someone who did not participate
in the excavation.
• Rapid results. Results
can be provided rapidly and
in advance of other site work
such as scaffolding. In comparison
with hand survey
methods, a huge volume of
primary data is captured
quickly. Photographic recording
of information and computer
analysis of all data
eliminate the need for most
field notes and vastly reduce
the time required to convert
field measurement information
into usable form, further
contributing to an improved
schedule.
• Data consistency. Experience
shows that if the features
are recorded manually
during an excavation, each conservation
professional will interpret the
detail differently. This may result in
nonhomogeneous drawings. If photogrammetry
is applied during the
entire project process, the documentation
can be standardized.
• Recording consistency. Photogrammetry
provides a consistent
level of recording. It is particularly
useful for objects or sites that are
difficult to survey with traditional
techniques. Extensive intricacies in
the structure’s detailing only necessitate
more image analysis and plotting
time off-site. One of the main
powers of the technique is its flexibility.
It can handle objects of virtually
any size, and it does not require
the recording positions of the cameras
to be known.
Limitations
• Complex technique. The technique
is still relatively complex and normally
requires the input of specialists.
As such, it is often not very
practical to apply on small tasks.
• High accuracy standards. The
standards of accuracy and thor-
Figure 7. Trinity College, Dublin. Full stereo coverage was taken in 1978 and analyzed
in 1990 for restoration work.
oughness produced are generally
very high. But on occasion they may
be too high for the project under
consideration.
• Value versus cost. The value for
price of any photogrammetric end
product will generally be satisfactory,
but the absolute cost in relation
to the project may simply be too
great. In short, although digital
close-range stereophotogrammetry
may be the most effective means to
record the object, there may not be
adequate financial means to use the
technology.
• Areas of application. It is not possible
to apply photogrammetric techniques
on all occasions or even to
ensure complete cover. The line-ofsight
requirement means that vegetation,
buildings, and other obstructions
may limit photographic coverage.
• Building interpretation. For the
production of line work, the interpretation
of badly eroded features
may not always be consistent, but
this can be overcome by an imagebased
product or a combination of
vector and raster data.
PROJECT PROFILE
Recently, Inspec was retained by the
University of Chicago to record, through
stereophotogrammetry, the building envelope
features of Rockefeller Chapel. The cornerstone
of the late gothic revival style
building was laid on June 11, 1926.
Construction was essentially completed by
late fall of 1928, with the official dedication
taking place on Sunday, October 28.
The structure consists of multiple wythe
brick back-up walls clad with Indiana bedford
limestone. Distinguishing architectural
features are present on all primary elevations,
including but not limited to carved
stones in the likeness of biblical figures,
text, and ornate tracery in-filled with
stained glass. With the exception of the roof
trusses and framing providing support for
the bell tower carillon, there are no additional
structural steel framing components
in the building. Large expanses of stained
glass fill the structure with a warm, filtered
light.
During the winter of 2002, Inspec performed
the initial critical examination of the
207′ bell tower as required by the city of
Chicago Façade Ordinance. The findings of
the survey yielded a determination of “safe
with maintenance and repair.” While no
immediate action was required as a result
of these findings, the information presented
in conjunction with the historical significance
of the structure provided justification
for a more comprehensive building envelope
study. (See Figures 8 through 13.)
The stereophotogrammetry recording
was performed during the summer of 2004.
Careful coordination with Lorraine Brochu,
Dean of External Affairs at the chapel; and
Barry O’Quinn, Senior Manager of Building
Envelope, Sheet Metal, and Masonry for the
campus was required to assure uninterrupted
use of the facility and temporary
protection of the grounds and bluestone
pedestrian walkways. One-hundred and
twenty 80-foot manlifts were used to provide
the required access and perspective of
each of the building’s varied exposures.
NO V E M B E R / D E C E M B E R 2004 I N T E R FA C E • 1 9
Figure 8. Open bed joint at interface of parapet wall and interior
integral gutter.
Figure 9: Inspection opening centered over open bed joint
identified corroded steel imbeds as the cause of the localized
distress.
Summary
Building owners with sophisticated
needs specific to the preservation and conservation
of historic structures are the most
likely to benefit from the information
derived through heritage building recording.
Lorraine Brochu writes that her work
as external affairs person for the University
of Chicago’s Rockefeller Memorial Chapel
frequently serves to promote the chapel not
only for its events, but also for the building
itself as a significant cultural, historical,
and architectural site. She states, “Peter
Trieb’s documentation of the chapel
through stereophotogrammetry gives me
the tools to identify the physical status and
needs of the building to the administration,
to the public, and to granting organizations
in order to make a strong argument to fund
the work necessary for the chapel’s preservation.
The black and white of words
describing a crack in the foundation pale in
comparison to a detailed set of images indicating
position, depth, and relative association
of the crack.”
Beyond the initial critical examination,
the project scope was revised to include the
balance of the building envelope features, or
the low rise partial and full elevations of the
main chapel. Barry O’Quinn recognized the
need as demonstrated through the pockets
of efflorescence that were presented at varied
random locations across the building
envelope. The immediate issue for the university
was how to develop a responsible
plan for a phased restoration/conservation
of the building’s cladding features. The photogrammetry
services promoted by Trieb
satisfied the University’s immediate needs
with respect to establishing the current
condition of the entire façade. In addition,
scaleable architectural building elevation
drawings would be realized through this
effort, which will subsequently be used in
pending bid processes for the required
rehabilitation of the exterior walls. The use
of stereophotogrammetry proved to be an
economical means to establish
baseline information without
the need for disruptive and costly
scaffolding that would typically
be used to gather the data.
The university, together with
a professional roof consulting
firm and an expert photogrammetrist,
are charting a carefully
planned restoration/conservation
effort for the Rockefeller
Memorial Chapel. In this
instance, the heritage recording
is the basis and foundation of
continued efforts towards a
common goal: embracing the
original fabric of the building
and the University’s vision for
campus-wide proactive management
of historically significant
structures.
CONCLUSION
There is an enormous stock
of aging buildings, and the
importance of conservation will continue to
grow, leading to additional requirements for
2-D and 3-D data for planning and documentation
purposes.
From an economic point of view and
with limited public budgets, it can be difficult
to justify the photography of the whole
of a building or ancient site just in case
there may be a problem. This comes down
to a value judgment on the importance of
that building or monument to that culture.
However, it is now being recognized through
the United Nations Educational, Scientific,
Figure 10: Spall in structural concrete pour below stone weatherings of balcony.
Figure 11: Failed joinery and cracked sloped stone weatherings over
balconies.
20 • I N T E R FA C E NO V E M B E R / D E C E M B E R 2004
and Cultural Organization (UNESCO)
world heritage designations that particular
monuments are important not
only nationally, but also globally.
Through the author’s involvement in
two UNESCO sites (Copan, Honduras,
and Fountains Abbey, England)
it is evident that greater funding has
been made available for survey and
conservation of these magnificent
sites.
Today, digital close-range photogrammetry
is well suited as a diagnostic
tool to generate the required
conservation, engineering, and
archival data for our historic buildings.
If the objects are very complex,
it can easily be the most economic
technique. With further developments
in automation, digital photogrammetry
is becoming faster and
more economical in the survey of
simpler objects, and these systems
require a reduced amount of interactive
work.
These tools will provide the caretakers
of our architectural heritage an even more
effective means to record the present,
understand the past, and plan for the
future.
Footnotes
1. Rectified photography is a technique
that can be implemented in a
very direct manner. The camera is
aligned parallel to the area of a
façade, scale is introduced in some
manner, and the resulting photograph
print is produced to this
defined scale. It allows for a rapid
but accurate record to be generat-
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NO V E M B E R / D E C E M B E R 2004 I N T E R FA C E • 2 1
Figure 12: Frost on the outside face of multiple white brick back-up at
inspection opening, indicating a fairly large volume of free moisture had
infiltrated the cladding components.
ed without the need for laborintensive,
time-consuming, handmeasured
survey.
2. A digital orthophotograph (from the
Greek ortho, meaning “right,”
“straight,” “plumb,” or “true”) is a
photo-quality digital image of surface
features in their geometrically
corrected, true map position.
Orthophotography is photography
that is fully corrected for perspective
and relief displacement.
Inaccuracies inherent in planerectified
photographs, due to relief
displacement, have been eliminated,
resulting in surface features
rendered at their highest degree of
positional accuracy. The digital
orthophotograph is effectively an
image map. The higher production
costs (compared to rectified photography)
are being reduced as
more automation is introduced and
computers get faster.
3. A solid model, in the context of
computer graphics, is the representation
of a physical/abstract
entity and phenomena not just for
the purposes of making pictures
(creating views), but to represent
their structure or behavior. The criteria
for development of the model
or hypothetical description is often
based on an analogy developed for
analysis. Models allow for simulation,
testing, and prediction of the
behavior of the entities
modeled for such purposes as
understanding, visualization, experimentation,
and learning.
4. Nondestructive testing (NDT) has
been defined as comprising those
test methods used to examine an
object, material, or system without
impairing its future usefulness.
The term is generally applied to
non-medical investigations of
material integrity. NDT is used to
investigate the material integrity of
the test object.
5. Two photographs on which the
same object or area of terrain is
pictured are taken, but from different
views or perspectives (different
camera stations) so as to afford
stereoscopic vision. The simple
shift in camera position simulates
our own biological stereovision that
allows us to see the world around
us in 3-D. Frequently called a
stereoscopic pair.
6. A theodolite is an optical surveying
instrument for measurement of
horizontal and vertical angles. It
consists of a sighting telescope
with crosshairs in the eyepiece for
focusing on the target, which can
be rotated in both the horizontal
and vertical planes. It is mounted
on a tripod and a spirit level is
used to indicate when the instrument
is horizontal. The angles are
read off graduated circles seen
through a second eyepiece in the
instrument.
22 • I N T E R FA C E NO V E M B E R / D E C E M B E R 2004
Donald Kilpatrick has been employed with Inspec since 1985.
During his tenure in the laboratory environment, he has evaluated
a broad range of roofing systems and components, with
an emphasis on construction defects. Don’s observations and
analysis of these components and assemblies has been utilized
in compliance and workmanship testing on both new
and existing construction and failure investigations. Most
recently, he has been assisting building owners with their
specific needs related to compliance with façade ordinance
inspections.
Donald Kilpatrick
Peter Belden Trieb is president and founder of Peter Belden
Trieb Inc., Heritage Building Recording & Conservation, in
Honeoye Falls, NY. The company provides specialized recording
services and technologies for documentation of the international
built heritage environment. Professional recording
services for museums, municipalities, commercial, religious,
institutional buildings, and period residences include digital
close-range stereophotogrammetry, rectified photography,
orthophotography, 3-D modeling, laser scanning, and manual
documentation. Trieb may be reached at www.petertrieb.com.
Peter Belden Trieb
Figure 13: Rust stains running down limestone cladding from the
underside of lead-coated copper gutter at base of stone weathering.