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Photomontage system for site planning
25 yearsof CAD Photomontage system for site planning P D Lever
The paper describes a photomontage system for accurately visualizing the effects of aherin9 a landscape, either by new buildings, new roads, urban renewal or any disturbance of the environment. An example is given of the use of photomontage in a motorway construction scheme.
speedily with objections and produce realistic and accurate visualizations of the final scheme. This helps to reduce delays, which, in turn, can reduce overall time and costs significantly, particularly where large teams and costly plant and equipment are concerned.
METHOD
photomontage, v&ualization, civil engineering
The general public in the UK is becoming increasingly discerning about the quality of the built environment and the inadequacies of traditional skills for considering the geometric and aesthetic qualities of new construction schemes. This has led to a search for better techniques for assessing quality before building. One such technique is computer-aided photomontage, which enables a computer-produced perspective drawing of a new scheme to be accurately superimposed on a photograph of the original landscape. The value of the photomontage system lies in its ability to produce a faithful pictorial representation of the changes brought about by new schemes for buildings, roads and urban renewal, or indeed any disturbance of the environment. This enables more rational discussions to be conducted, for example, at planning enquiries, since local residents and others affected by the environmental changes can be more readily assured that an accurate impression of the scheme is being presented through the impartiality of the computer system. The consequences of design decisions can be more readily visualized at an early stage in planning. From the designer's point of view, there is great attraction in the new possibilities derived from the photomontage system. It enables him/her to deal more
To use the system, the designer's dimensional sketches are coded and fed into the computer, where a 3D geometric model is created. Standard hidden-line graphics enable the geometric model to be processed and a perspective drawing to be produced. With photomontage, it is critical that the computer-produced perspective picture should be superimposed exactly over the photograph of the original landscape. The photomontage system calculates the viewing parameters of the camera which produced the landscape photograph, using positional data of control points in the landscape. These viewing parameters are then applied to produce a perspective drawing with the hidden lines removed. An actual example carried out by the CAD Centre with the Eastern Road Construction Unit is shown in Figure 1. The top part of Figure 1 is a photograph of the original landscape, and the ends of the telegraph posts are used as control points for the photomontage system. The middle part is a computer-produced perspective drawing using the photomontage viewing parameters. The bottom part is produced by superimposing the computer-produced drawing on the landscape photograph. It provides a faithful pictorial representation of the new motorway in its environment. This example was used at a public enquiry on one of the Unit's proposed motorway schemes.
Viewing parameters At the time of publication in Computer-AidedDesign,Volume 5, Number 2, April 1973, the author's affiliation was as follows: Computer Aided Design Centre, Madingley Road, Cambridge CB3 0HB, UK Paper received : 10 October 1972. Revised : 12 January 1973
volume 25 number 6 june 1 9 9 3
The photomontage program is based on the assumption that a photograph is uniquely defined by nine parameters: the camera position Xe, Ye, Z~, the camera orientation A, the camera elevation B, the camera tilt G, the scale factor S, and the focal centre Xp, Yw
0010-4485/93/060387-02 © 1993 Butterworth-Heinemann Ltd
387
P D Lever Field and photograph positional data
Ph°t°m°ntag¢ pr°gram I
User-defined
I
objects
THINGS
Hiddenlineprogram
Perspective drawing
of structure
Figure 2. Features of landscape provide control points and, in turn, positional data [The photomontage system calculates the viewing parameters of the camera used to produce a landscape photograph. These parameters, together with the THINGSpackage, were used to produce a perspective drawing with the hidden lines removed.]
Figure 1. Example of use o/'photomontage system [The top part of the figure is a photograph of the orginal landscape using the posts as control points. The middle part shows a computer-producedperspectivedrawing using the viewingparameters, and the bottom part is a result of superimposingthe computer-produced drawing on a landscape photograph. Illustration provided by courtesy of the Eastern Road Construction Unit.] Some of these parameters will be known. For example, the camera position will be surveyed and the focal centre is normally at the centre of the photograph. Others can be guessed; for example, the camera tilt and elevation are usually small, and the scale factor is merely the camera focal length multiplied by the enlargement factor. The photomontage program finds precise values of the guessed parameters by a least-squares minimization technique. The number of surveyed control points needed depends on the number of unknown parameters: for example, if the camera position only is known, then a minimum of three control points is required, although more are recommended for use as a crosscheck.
Geometric description A coded geometric description of the structure for the hidden-line program consists of lists of point coordinates defining the vertices of each object, and of polygons
388
defining the boundary points of the structure's opaque faces. Because of the tediousness of preparing this data, the CAD Centre has developed a package called THINGS, which enables a user to define a structure in terms of basic primitive solids, for example boxes, cylinders, ruled surfaces etc. It is basically a set of FORTRAN callable subroutines allowing a user to define his/her own library of subroutines in terms of basic primitives, and position objects in space in an easily understood manner in order to assemble an object for subsequent viewing.
SYSTEM The photomontage system is shown in Figure 2. The perspective drawing of the construction scheme is produced using the hidden-line program at the CAD Centre. This program requires as input the viewing parameters of the photograph and a geometric description of the structure.
CONCLUSIONS The photomontage system has been incorporated into a comprehensive graphics system at the CAD Centre. This system includes such other facilities as realtime simulated movies and greyscale pictures.
ACKNOWLEDGEMENTS The author would like to acknowledge R G Newell and C B McGee who developed the basic algorithms and wrote the photomontage program. The photomontage system, and the hidden-line graphics and other facilities, were available at the CAD Centre at the time of the writing of this paper.
computer-aided design
The paper describes a photomontage system for accurately visualizing the effects of aherin9 a landscape, either by new buildings, new roads, urban renewal or any disturbance of the environment. An example is given of the use of photomontage in a motorway construction scheme.
speedily with objections and produce realistic and accurate visualizations of the final scheme. This helps to reduce delays, which, in turn, can reduce overall time and costs significantly, particularly where large teams and costly plant and equipment are concerned.
METHOD
photomontage, v&ualization, civil engineering
The general public in the UK is becoming increasingly discerning about the quality of the built environment and the inadequacies of traditional skills for considering the geometric and aesthetic qualities of new construction schemes. This has led to a search for better techniques for assessing quality before building. One such technique is computer-aided photomontage, which enables a computer-produced perspective drawing of a new scheme to be accurately superimposed on a photograph of the original landscape. The value of the photomontage system lies in its ability to produce a faithful pictorial representation of the changes brought about by new schemes for buildings, roads and urban renewal, or indeed any disturbance of the environment. This enables more rational discussions to be conducted, for example, at planning enquiries, since local residents and others affected by the environmental changes can be more readily assured that an accurate impression of the scheme is being presented through the impartiality of the computer system. The consequences of design decisions can be more readily visualized at an early stage in planning. From the designer's point of view, there is great attraction in the new possibilities derived from the photomontage system. It enables him/her to deal more
To use the system, the designer's dimensional sketches are coded and fed into the computer, where a 3D geometric model is created. Standard hidden-line graphics enable the geometric model to be processed and a perspective drawing to be produced. With photomontage, it is critical that the computer-produced perspective picture should be superimposed exactly over the photograph of the original landscape. The photomontage system calculates the viewing parameters of the camera which produced the landscape photograph, using positional data of control points in the landscape. These viewing parameters are then applied to produce a perspective drawing with the hidden lines removed. An actual example carried out by the CAD Centre with the Eastern Road Construction Unit is shown in Figure 1. The top part of Figure 1 is a photograph of the original landscape, and the ends of the telegraph posts are used as control points for the photomontage system. The middle part is a computer-produced perspective drawing using the photomontage viewing parameters. The bottom part is produced by superimposing the computer-produced drawing on the landscape photograph. It provides a faithful pictorial representation of the new motorway in its environment. This example was used at a public enquiry on one of the Unit's proposed motorway schemes.
Viewing parameters At the time of publication in Computer-AidedDesign,Volume 5, Number 2, April 1973, the author's affiliation was as follows: Computer Aided Design Centre, Madingley Road, Cambridge CB3 0HB, UK Paper received : 10 October 1972. Revised : 12 January 1973
volume 25 number 6 june 1 9 9 3
The photomontage program is based on the assumption that a photograph is uniquely defined by nine parameters: the camera position Xe, Ye, Z~, the camera orientation A, the camera elevation B, the camera tilt G, the scale factor S, and the focal centre Xp, Yw
0010-4485/93/060387-02 © 1993 Butterworth-Heinemann Ltd
387
P D Lever Field and photograph positional data
Ph°t°m°ntag¢ pr°gram I
User-defined
I
objects
THINGS
Hiddenlineprogram
Perspective drawing
of structure
Figure 2. Features of landscape provide control points and, in turn, positional data [The photomontage system calculates the viewing parameters of the camera used to produce a landscape photograph. These parameters, together with the THINGSpackage, were used to produce a perspective drawing with the hidden lines removed.]
Figure 1. Example of use o/'photomontage system [The top part of the figure is a photograph of the orginal landscape using the posts as control points. The middle part shows a computer-producedperspectivedrawing using the viewingparameters, and the bottom part is a result of superimposingthe computer-produced drawing on a landscape photograph. Illustration provided by courtesy of the Eastern Road Construction Unit.] Some of these parameters will be known. For example, the camera position will be surveyed and the focal centre is normally at the centre of the photograph. Others can be guessed; for example, the camera tilt and elevation are usually small, and the scale factor is merely the camera focal length multiplied by the enlargement factor. The photomontage program finds precise values of the guessed parameters by a least-squares minimization technique. The number of surveyed control points needed depends on the number of unknown parameters: for example, if the camera position only is known, then a minimum of three control points is required, although more are recommended for use as a crosscheck.
Geometric description A coded geometric description of the structure for the hidden-line program consists of lists of point coordinates defining the vertices of each object, and of polygons
388
defining the boundary points of the structure's opaque faces. Because of the tediousness of preparing this data, the CAD Centre has developed a package called THINGS, which enables a user to define a structure in terms of basic primitive solids, for example boxes, cylinders, ruled surfaces etc. It is basically a set of FORTRAN callable subroutines allowing a user to define his/her own library of subroutines in terms of basic primitives, and position objects in space in an easily understood manner in order to assemble an object for subsequent viewing.
SYSTEM The photomontage system is shown in Figure 2. The perspective drawing of the construction scheme is produced using the hidden-line program at the CAD Centre. This program requires as input the viewing parameters of the photograph and a geometric description of the structure.
CONCLUSIONS The photomontage system has been incorporated into a comprehensive graphics system at the CAD Centre. This system includes such other facilities as realtime simulated movies and greyscale pictures.
ACKNOWLEDGEMENTS The author would like to acknowledge R G Newell and C B McGee who developed the basic algorithms and wrote the photomontage program. The photomontage system, and the hidden-line graphics and other facilities, were available at the CAD Centre at the time of the writing of this paper.
computer-aided design