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Fig.1 3-d model representing Hatfield Aerodrome.
THREE-DIMENSIONAL MAPPING AND AS-BUILT COMPUTER MODELLING BY ANALYTICAL
PHOTOGRAMMETRY
R.M.Littleworth, D.M.Stirling, J.H.Chandler, Engineering Surveying Research Centre, Department of Civil
Engineering, City University, Northampton Square, London EC1V OHB, UK. ISPRS. Commission V
ABSTRACT:
The paper describes how and why analytical photogrammetry, interfaced with a CAD system, has been used to create
3-dimensional computer models of development sites and engineering structures. Topics covered include: problems in
combining data sources of different accuracy (e.g. aerial and close-range photographs and detail ground
surveys)compromises necessary to idealise the geometry of the real world so that it can be represented by the CAD
elements; and the uses to which these CAD products have been put. Examples include: gantry cranes, chemical plant and
industrial and inner-city redevelopment sites.
KEY WORDS: CAD/CAM, Close-range, Industrial, 3-D, Visualization.
INTRODUCTION
Most of the work undertaken in close range industrial
photogrammetry is involved with dimensional control.
Typical applications include checking the shape of
microwave, radar antenna and machine tools
(Fraser,1986). These projects have involved the
automated measurement of premarked targets utilising
specialised photography taken from pre-determined
camera stations and have achieved accuracies of up to one
part in a million (Fraser,1992). Other examples have
provided information for the design of add-on
components such as an aircraft hush kit (Fraser, 1986) and
for computer-aided design in the automotive industry
(Wahl,1984). However most of these applications have
involved the measurement of objects or components
which are comprised of ideal geometric shapes. Until
recently very little work has involved the computer
representation of irregular 'as-built' features.
With the introduction of industry wide CAD packages
(e.g. Microstation, Autocad) the potential for introducing
analytical photogrammetric techniques to new users has
greatly expanded. This has involved exploiting the CAD
potential of modern photogrammetric instrumentation,
however, the accuracy achievable creating 3-dimensional
computer models is restricted given the geometric
restraints imposed by the CAD system. To fully realise the
potential of these new areas traditional producers of maps
and plans must learn to adapt themselves and their
products to exploit the new systems.
The Engineering Photogrammetry Unit (EPU) was
launched in 1988 following the purchase of an Intergraph
Intermap Analytic Photogrammetric Workstation (IMA)
by City University. EPU has the task of exploiting and
adapting research undertaken within the university and
applying this to industry by way of offering a bureaux
service for both commercial and research contracts.
Income generated in this way is used to purchase new
equipment and fund further research by the university.
In order to provide the potential new photogrammetric
users with the 3- dimensional product they require a
change in approach and attitude to the traditional
photogrammetric product was required. This has involved
learning some of the work practices of potential users and
using computing techniques that most photogrammetrists
would not require. It has also proved necessary to
compromise the photogrammetrists’ traditional desire for
accuracy in order that a geometrically ‘imperfect’ object
can be more easily modelled within a CAD environment.
To illustrate the evolution of the 3-dimensional
photogrammetric product, examples of some recent
projects undertaken by EPU will be given.
Hatfield Aerodrome
This was one of the first projects undertaken by EPU and
is closely related to conventional mapping projects.
Although a 3-dimensional project it is based upon a
traditional large scale 2-dimensional specification. The
requirement was for a computer model for use in the
