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ARCHITECTURAL PHOTOGRAMMETRY
Ray Manning
Spring Quarter 1979
Univ. of Fla.
Preservation
TABLE OF CONTENTS
1. INTRODUCTION
2. PROBLEMS SOLVED IN RESTORATION
3. OPERATIONAL PROBLEMS
4. CAMERAS
5. SINGLE IMAGE RECTIFICATION
6. TWO IMAGE RESTITUTION
7. SPECIAL APPLICATIONS
8. BIBLIOGRAPHY
INTRODUCTION TO ARCHITECTURAL PHOTOGRAMMETRY
Photogrammetry is the science of surveying or map
making by means of measurements taken from photographs.
Principles have been developed that allow photographs
of ground planes, structures and landscaped areas to
be accurately measured in three dimensions. The three
dimensional measurements can then be transferred to
two dimensional recording techniques such as arch-
itectural drawings.
The purpose of architectural documentation is to
preserve the precise physical characteristics and the
ambience of a structure, monument or excavation. It
should be in the form of an analytical and unbiased
critical report accompanied with drawings and with
photographs to support it's authenticity.
The documentation must retain the aesthetic and
historical value as well as unexplored traits, whose
significance may not be known until future research
uncoverE there and their importance.
The problem of accurately recording a structure
or area of significance in a short period of time can
usually be accomplished easily with photogrammetry
techniques.
Photogrammetry provides a practical and economical
answer to recording buildings or features in their
true three dimensional state. This replaces ordin-
nary hand measuring and drawing techniques that
would prove to be too time consuming or impossible
to accomplish.
Photogrammetry is ideal where an immediate docu-
mentation of a structure is required due to impending
or inevitable destruction. It provides a precise and
impersonal manner in which to preserve the complete
original character of the building which may be lost
in an restoration effort or the destruction of the
building.
The expense of recording with photogrammetry
techniques is related to the degree of accuracy that
is required for a specific case. Recent technological
advancements in equipment have produced accuracy to
within 1 mm.
PROBLEMS SOLVED IN RESTORATION WITH PHOTOGRAMMETRY
Photogrammetry locates as well as solves many
problems that arise during the study and documenta-
tion of a building. This allows the structure to be
more easily restored because these problems are
discovered and resolved before the restoration begins.
Obvious deformations in the structure due to
sinking foundations, excessive loading,earthquakes
and other minor causes must be accurately recorded
in order to preserve the actual character and orig-
inal state of the structure. The extent and type of
deformation as well as the extent of restoration to
be done, determines the type of survey to be used.
Most cases can be easily recorded with photogrammetry
techniques.
The unobvious deformations that are not easily
located by a cursory examination will be lost if not
recorded before the restoration of a structure is
begun. They may also develop into unforseen problems
during the restoration process. Close study of the
structure with photogrammetry techniques can usually
uncover these deformations with relative ease.
Photogrammetry can be used to locate very small
optical refinements in a structure that appear as
small dimensional deviations.
The optical refinements occur as variations of
adapted normal dimensions and deviations from a
straight line or plane that is supposedly horizontal
or vertical. An example of this is the column entasis
deviation of 17.5 mm or the corona deviation of 1/100
on the cornice of the Parthenon. Intended deviations
such as these must be located in order to assure an
accurate documentation and their preservation in the
restoration of A building.
The problem of recording irregularities and com-
plexities in building designs and materials can be
easily solved with photogrammetry techniques. Undu-
lating, asymmetrical and irregularly shaped facades
and walls which would have consumed many man hours
to measure, can now be cut to a fraction of that time.
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Curved surfaces, interpenetrations of curved planes
sculptures and intricate structural members are very
difficult, if not impossible to measure and properly
transfer into architectural drawings. The use of
photogrammetry contour plotting with stereopairs of
photographs will easily measure the most complicated
shape to within 1mm. of accuracy.
Frescoes and mosaic designs can be easily and ac-
curately recorded with photogrammetry to allow easy
and accurate reassembly or reproduction in a restor-
ation effort.
Accurately recording traces of hand hewing, dowels,
lifting holes and previous restorations or remodeling
on structural members can easily and accurately be
accomplished with photogrammetry. This preserves the
character and history of a structural member or por-
tion of building fabric before it is hidden in a new
restoration of the building.
OPERATIONAL PROBLEMS WITH PIIOTOGRAMMETRY
Exterior surroundings and interior spatial
arrangements of a building to be documented may often
impose restrictions that must be delt with. This deter-
mines the type of instruments and photogrammetry
methods that will be used to obtain the desired results.
When the distance from the camera to the building is
too short for a stereocamera, two widely spaced individ-
ual cameras may be used in it's place to attain the
proper results.
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STEREOCAMERA INDIVIDUAL CAMERAS
The problem with this is if the cameras are placed
at too great an incline from the principle axis,
restrictions occur due to limitations of the equipment.
Modifications must be done to the equipment to com-
pensate for the large incline angles. A number of the
newer stereocameras are constructed with lenses that
are wider then the early models but not as wide as the
lense on the individual type camera. This recent
development has helped to alleviate some of the pro-
blem.
If vegetation interferes with a camera position
that is perpendicular to the wall to be photographed,
the camera may be relocated to a corner of the wall.
This allows a clear photograph to be taken but
requires the use of the more complicated analytical
restitution technique in place of the analogue res-
titution or rectification process.
PHOTOGRAMMETRY CAMERAS
Photogrammetry requires the use of special
cameras that are designed for the purpose of
attaining a high degree of accuracy. The most
commonly used are the stereometric and the
individual camera.
The older phototheodolites are periodically
used for site architectural documentation but
are rarely used for building documentation.
The amateur 35 mm and 24 format cameras
can also be used for photogrammetry but are
limited in their accuracy and the type of equip-
ment that can be used to process them.
A. Phototheodilites
The phototheodolite is designed primarily for
topographical surveying and is therefore usually
unsuitable for building surveying. The problem
with this type of camera that limits its use for
building documentation are it's narrow field of
view and it's focal length which is set at infinity.
Despite the limitations, due to it's high
degree of accuracy it is well suited for aerial
documentation of sites.
B. Stereometric Camera
The stereometric camera or stereocamera is
composed of two camera bodies mounted on a
tubular base of a fixed .length. The fixed length
and geometry of the base and camera positions
set a maximum and minimum limit of operation.
These limits set the range of the camera to
object distance and the degree of accuracy.
Operation of the camera within these limits
produces highly accurate results.
The stereocamera is easier to use than the
two individual cameras because there is no need
to maintain a crucial measurement between the
two cameras since it is already fixed.
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A drawback to the stereocamera with a normal
field of view is that it must be placed far
enough away from the subject to allow the entire
facade or wall to be photographed at once.
Recent developments in stereocameras has pro-
duced a wide angle lens with a short principal
distance that reduces the required distance to
the object This greatly reduces one of the
camera's biggest drawbacks.
Glass plates are the most widely used type
of photographic vehicle. This is due to the fact
that they produce a reliably flatter image than
roll or cut film. Film may have air pockets
between it and the film support or deformations
due to tension from the film transport mechanism.
C. Individual Metric Camera
The small format individual camera can be used
to photograph an object from two different posi-
tions or two cameras can be used at two different
positions simultaneously. Due to it's smaller size
and nature, it is more versatile then the stereo-
camera or phototheodolite and produces a quicker
documentation.
The advantages of this camera over the stereo-
camera (standard model) are the ease with which
it can be handled and set up, it's short principle
distance and wide field of view.
The camera uses roll or cut film as well as
the highly accurate glass plates.
Most late model cameras have the ability to
be dispositioned with reference to the object that
is to be photographed. This offsets the principal
point of photography to allow full facade photo-
graphs to be taken to one side of obstacles
object N obstacle
,-normal principle point
- _dispositioned principle
S.point of photography
Recent developments in the manufacture of these
cameras has lead to larger focal lengths while
still retaining a large field of view. This
improvement has greatly expanded the use and
versatility of the camera and was accomplished
with the following methods;
1. adjustable displacement of the lenses by
spiral or translator movement.
2. rings of different thicknessess placed
between the lens and the camera body.
3. additional lenses attached to the front
of the primary camera lens,
4. interchangeable lenses.
SINGLE IMAGE RECTIFICATION
Documentation or surveys of objects on a single
plane such as a flat or nearly flat facade can be
accomplished with a single photograph. This is
referred to as single image photogrammetry and is
the most commonly used technique for simple eleva-
tions and objects having low surface depth such
as mosaics and frescos.
A photograph of a building that was taken on
an upward incline results in parallatic distortion
of the building image. The distorted image must be
corrected to present a physically and visually
correct image that can be accurately measured.
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The photographical process expands the uses of
single image photogrammetry as well as saves time
and expense. Examples of this are the streetscape
photographs and the supplementing of architectural
drawings with rectified photographs.
Individual photographs of a street facade can be
rectified to correct the building images and then
assembled into a photomosaic.
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The correction process is called rectification
and can be produced either graphically, optically,
photographically or analytically.
A. Graphical Rectification
The graphical rectification process is the
earliest of the rectification techniques and was the
most extensively used in the early days of photo-
grammetry. It was used until the end of World War
II, at which time the photographical method replaced
it. The process was very time consuming and proved
to not be highly accurate.
The process consisted of drawing perspective
lines on the photograph and then converting them
to a graphically correct image of the facade.
B. Optical Rectification
Optical aids are used in this process to convert
the distorted image into a corrected form. Due to
its poor degree of accuracy and the specially train-
ed personnel required it is generally used only
to complete details on a already corrected image.
The end product of this process is the same as that
which is derived from the graphical rectification.
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C. Photographical Rectification
The photographical rectification process is more
accurate then the previously described processes
but has to deal with equipment limitations.
This rectification process reverses the effect
that caused the distortion in the first place.
This is accomplished by placing the photograph
of the distorted image on a tilted table within
the rectifier and then rephotographing it. A newely
distorted photograph of the originally distorted
photograph produces a corrected image of the build-
ing.
The normal rectifier can produce results only
from a photograph that is taken at no more than
15 degrees upward incline. The equipment must be
modified to accommodate photographs that are
taken above 15 degrees, with a maximum of 30 degrees.
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TWO IMAGE STEREORESTITUTION
The two image method is not limited to a single
plane or nearly flat object but can be used for
the restitution of three dimensional objects.
The principle is based on the intersection of
two corresponding rays from two photographic images.
The coordination and measurements of these rays are
processed by one of the following methods;
A. Graphical restitution
B. Stereoscopical restitution
C. Stereophotogrammical restitution
The above methods usually require only two mea-
surements to be taken on the object, one horizon-
tally and one vertically. Additional measurements
will give a higher degree of accuracy.
The type of restitution to be used is based upon
the restrictions of the object and it's surroundings,
the nature of the problem and the desired final
output.
A. Graphical restitution
The graphical method is the oldest of the three
and was widely used until 1945 when it was replaced
by the two newer and more accurate methods. It is
rarely used today because it requires a great deal
of time to produce and is not very accurate.
The principle is similar to the single image
method of graphical rectification where two con-
verging rays are located and measured by optical
and graphical means.
B. Stereoscopic restitution
The stereoscopic plotter uses photographs of
an object that are taken at slightly different
angles and then projects them on a tracing table
that produces a three dimensional model of the
object that is then studied stereoscopically.
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The projection is focused with respect to a given
plane and by refocusing, several different planes
can be located and plotted. The measurements of
the various planes can be assembled to produce
three dimensionally measured facade or object.
The stereoscopic technique is generally used
for small and simple structure.
The principle drawback to this method is the
limited availability of camera positions that
can be used to attain desired results. The photo-
graphs that are to be used in this technique
usually must be taken paralell and perpendicular
to the desired wall plane with a maximum variation
of 10 degrees. The limited variation of 10 degrees
can be easily accommodated by normal restitution
equipment. Modifications to the instruments are
required to process photographs taken at 30 Or
60 degrees.
The exact restitution instrument to be used
depends on the accuracy required and the position
from which the photograph was taken.
The output of most stereoscopic equipment is
in the graphical form.
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C. Stereophotogrammical restitution
The stereophotogrammetry or analytical resti-
tution is generally used for large complicated
structures, rugged terrain and streetscapes that
require a high degree of accuracy. Analytical
restitution is based on a perspective relationship
between the true object and it's photographed
image. Mathematical expressions of this relation-
ship enable measurements to be taken on a part-
icular plane. By establishing a number of differ-
ent measured planes the object can then be
accurately surveyed.
The technique is more versatile and accurate
than stereoscopic or graphical restitution and
has the following advantages!
1. it is not limited by any camera angle
2. the plotter can use a photograph taken
by non-photogrammical cameras and still
maintain a reasonably high degree of acc-
uracy.
3. it is very efficient at plotting patterns
and contours on curved surfaces.
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The biggest advantage of the stereophotogram -
mical plotter is it's ability to use photographs
that are taken frop a corner angle. The corner
photograph possesses much more information than
a frontal phtotgraph.
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A drawback to stereogrammical restitution is
that the movement of the measuring point is not
correlated with the field coordinated measuring
system. This does not allow specific points to
be read on a particular horizontal or vertical
cross section. It is therfore only possible to
record profile points that are naturally visible
on a building such as downspouts or brick courses.
Another disadvantage is it's inability to
produce a output of continuous lines unless com-
puter plotting is employed.
SPECIAL PHOTOGRAMMETRY APPLICATIONS
A valuable special use for rectified photo-
graphs is to use them in conjunction with hand
drawings. Details of the wall surface and building
materials can easily and accurately be recorded.
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Entire sites can easily be surveyed and docu-
mented from the air in a fraction of the time
required to do it by hand.
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Horizontal as well as vertical contour lines
can be easily plotted to reproduce the character
of the terrain surrounding the surveyed object.
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Profiles and projections of entire portions of
a city with vertical sections at desired points.
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Photogrammetrically produced perspectives in
the form of axonometric perspective projections.
This gives an even three dimensional relationship
over the entire area to be studied with the
scale the same over the entire output sheet.
1I3BI OGRAPIIY
1. American Society of Photogrammetry, Manual of
Photogrammetry, Washington D.C., 1966.
2. American Society of Photogrammetry, Close-
Range Photogrammetry, Washington D.C. 1971.
3. Badekas, John, Photogrammetric Surveys of
Monuments and Sites, North-Holland Publishing
Co. New York, N.Y.
4. Church, Earl and Quinn, Alfred 0., Elements
of Photogrammetry, Syracuse University Press,
1948, Syracuse, N.Y.
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