THE DESIGN AND SIMULATION OF VIDEO DIGITIZING
BY USING THREE-DIMENSIONAL CAD-MODELS
Ms. Katri Oksanen, M.Sc. (Eng.)
Researcher
The Institute of Photogrammetry and Remote Sensing
Helsinki University of Technology
Finland
Commission V, Working Group 3
KEY WORDS: Design, Simulation, Visualization, Three-dimensional CAD model, Measurement Model, Close_range
ABSTRACT
This paper describes the use of three-dimensional CAD-models in the design of a measurement model for video digitizing. The
paper also describes the simulation of the measurements defined by this measurement model. A tool made for this purpose, the
Measurement Model Design tool (MMD) is presented. With the tool, the measurement can be designed using three-dimensional
CAD-models of the object and measuring environments. The user can select from various camera models. The intersection
precision is calculated using limiting error propagation. Calculated precision values are visualized in 3D object space in
AutoCAD. Also simulated images are shown. After its creation, the measurement model can be used to control or assist the actual
measurement. The MMD tool and its simulation part form an experts’ tool for planning video digitizing.
1. INTRODUCTION
For the planning of traditional photogrammetric measurements
like aerial photogrammetry, there is plenty of theory and
knowledge available. The planning of video digitizing in large
scale applications, such as the quality control or reverse-
engineering tasks, differs from these traditional measuring
situations. It is typical to use convergent images. The shape of
the object can complicate the camera placement. To cover the
whole object, it is needed to be surrounded by cameras. The
cameras have to see overlapping areas. Especially in industry
the measuring environment can be really restrictive. On the
other hand, the accuracy requirements are usually very high.
The placement of the cameras demands various and often
almost opposite restrictions to be taken into account. The
three-dimensional measurement demands three-dimensional
planning.
1.1 The measurement situations
In quality control measurements there is usually a CAD-model
of the object available. The idea of the measurements is to
check how well the real object meets the design. In reverse-
engineering the purpose of the measurements is to produce a
CAD-model. However, in this case an approximate model can
be used in the planning of the measurement.
1.2. The measurement model
The concept of the measurement model includes the sensors
and the measuring points (or features). It includes sensor
exterior orientation (the projection center coordinates and
rotations) and interior orientation information. Interior
orientation can be taken either from calibration data or from
user-defined ‘ideal’ values.
The measurement model can also produce command files for
the sensor control, or its information can be used as starting
values for the measuring system (for example, sensor
orientation, approximated image coordinates and so on).
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Some general aspects of designing video digitizing are
introduced in chapter two. The measurement model design tool
(MMD) and its use are described in chapter three. The
simulation of the measurements designed with this way are
explained in more detail in chapter four. At the end some
conclusions are made.
2. THE DESIGN OF VIDEO DIGITIZING
The design of photogrammetric network in close-range
applications is a complicated task. There is not one right
design or one best design available. From many possible
designs the suitable one for every situation have to be selected.
Many requirements and constraints are opposites and the
stability between them has to be found. One way to find, if
requirements and constraints are full-filled, is simulation.
2.1. General aspects on close-range
photogrammetric measurement
design of
The photogrammetric system bases on the collinearity
condition. This condition defines that the image point, the
projection center of a camera and the object point lie on the
same line. The object coordinate measurement is based on this
condition. The system is not ideal, for example, lens distortions
have to be taken into account.
The design has mostly based on experience of
photogrammetrists. In last years there have been efforts to
build automated design systems or simulation systems for
designing of close-range photogrammetric applications
(Luhmann, 1994; Mason, 1994; Cowan, 1988). The main
purpose in our work has been to buildt an experts’ tool. By
simulation, it is possible to get information about achievable
precision and reliability of the measurements.
In real measurement situations there are many restrictions. For
example, the best possible imaging geometry is often hard to
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
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