can easily be observed. The designed geometry is used for
simulation of precision values. Calculated precision measures
are visualized in AutoCAD with MMD tool.
3.1. Technical information about the tool
The measurement model design tool works in AutoCAD
environment. The tool is written by AutoLISP-command
language. It utilizes AutoCAD’s Advanced Modeling Extension
(AME) package. The tool enables the design of measurements
in 3D. The restriction of the tool is, so far, that the object has
to be modeled as solid model. The tool has been developed in
3D2000 project. The base of the tool is written at VTT,
Technical Research Centre of Finland, in Oulu by Hannu
Kallio-Kokko and Petri Pajumäki. The further development of
the tool's photogrammetric part is done by the author of this
paper in Helsinki University of Technology. The design part
(AutoLISP-functions) works in AutoCAD both in MS-DOS-
and UNIX-environments.
The simulation part of the tool has been written in C-language
and it works for the present in UNIX. Simulation calculation
part use functions originally made for the Mapvision System.
These have been connected to the design tool in AutoCAD.
The simulation part uses the information created by the MMD
tool. The calibration files of the Mapvision System can also be
utilized in simulation. The results of the simulation (precision
measures) are visualized in AutoCAD by the MMD tool.
3.2. The use of the tool
The MMD tool was originally made for CAD-based graphic
measurement planning for rangefinder-based 3D coordinate
measurements (Ailisto et al., 1995). The tool can, for example
produce command files to control the rangefinder. Later the
planning of photogrammetric measurement is added to the tool.
The simulation part is so far done only for the photogrammetric
measurements. The simulation part is possible to expand for
other measurement types, for example the rangefinder
measurements, too. In this paper only the photogrammetric
functions of the tool are described.
3.3 The definition of measuring situation
The tool utilizes AutoCAD's graphic representation properties.
The basic data used in design are the solid model of the object
and the three-dimensional CAD-model of measurement
environment, which is optional. The measurement environment
can be modeled by photogrammetry, laser-profiling, or
theodolites. Also extruding of building plans can be a useful
way to get the rough model of workspace. At present, the
workspace model is only a visual help for the designer. It is
planned to be taken into account in the visibility calculations.
The model of the object can be, for example, a design of the
object (quality control tasks), or an approximated model
(reverse-engineering tasks), or an old model (based on earlier
measurements). Various types of camera models can be used. If
camera calibration files are available, they can be used.
Another case is to use an old calibration file of the similar
camera type. The last possibility is to use ideal pinhole camera
for the planning of measurements. The user of the tool defines
which kind of camera model is used.
434
3.4. The sensor placement process
The designer chooses the number of cameras. The camera
sensors are placed around the object. The target point for cach
camera is defined. The camera parameters (for example,
camera constant, image width and height) can be altered during
the design. Camera places and target points can also be
changed as long as suitable camera geometry is founded. The
MMD tool does not include any artificial intelligent for the
sensor location. This means that the designer of the network
decides, for example, how many cameras are used, which kind
of cameras are used and how they are located. In practice, the
designer puts each camera into image and shows the target
point for each camera. After locating cameras, designer can
visualize how different images cover the object. Camera
placements, orientations and parameters can be changed, if
wanted. In the present version of the tool, the maximum of four
cameras can be placed at time.
3.5. The object points location process
Object points can be selected after fixing the camera locations.
There are various strategies to select object points to be
measured. Points can be selected one by one, or points can be
selected using profile or raster definitions. With profile and
raster definitions, the points are selected automatically from
selected line or area defined by the cursor. The distance
between the points is given by the designer. The visibility
check is made before an object point is accepted. If the point is
not visible for at least two cameras, it is rejected. After
deciding the locations of measuring points, a simulation stage
can be made. The figure 1 is an example of three-dimensional
measurement plan.
Figure 1. An example of measurement model. The camera
placements are shown with big crosses and object points with
smaller crosses.
MMD tool saves the plan as an AutoCAD drawing file (DWG).
It also produces input files for the simulation part. These files
include the camera positions and orientations and object point
coordinates. In photogrammetric measurements the simulated
image coordinates and the sensor orientation information can
be used as approximated starting values for the measurement
system.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
3.6. The c
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