• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 Introduction
 Problems solved in Restoration...
 Operational problems with...
 Photogrammetry Cameras
 Single Image Specification
 Two Image Stereorestitution
 Special Photogrammetry Applica...
 Bibliography






Architectural photogrammetry
CITATION SEARCH THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00099614/00001
 Material Information
Title: Architectural photogrammetry
Physical Description: 28p. ; ill.
Language: English
Creator: Manning, Raymond L.
Publisher: Raymond L. Manning
Place of Publication: Gainesville, Florida
Publication Date: 1979
Copyright Date: 1979
 Subjects
Subjects / Keywords: Historic preservation
Architectural photogrammetry
Architecture -- Florida   ( lcsh )
Architecture -- Caribbean Area   ( lcsh )
 Notes
General Note: UF AFA Historic Preservation document 465
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UF00099614:00001

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
    Introduction
        Page 3
        Page 4
    Problems solved in Restoration with Photogrammetry
        Page 5
        Page 6
        Page 7
        Page 8
    Operational problems with Photogrammetry
        Page 9
        Page 10
    Photogrammetry Cameras
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
    Single Image Specification
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
    Two Image Stereorestitution
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Special Photogrammetry Application
        Page 28
        Page 29
        Page 30
    Bibliography
        Page 31
Full Text


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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