The software of the system consists of three main
parts:
Recording
Tracking
Analysis
2.1 Recording
The recording transfers a sequence if images from an
external source to the internal Video Disc of the
TrackEye system. A video disc file can be generated
using three different sources:
Standard video sources from a video or a video
tape recorder.
Film scanner for 16 mm cine film
Selected copies or sequences from earlier
recorded video disc files.
22 Tracking
The tracking is automatic with manual supervision
and is able to follow 95 objects simultaneously. The
points are defined by the user in the first image by
positioning a cursor on the point of interest.
Interactive tools for zooming, backtracking, motion
view survey etc. are provided. The manual
supervision can be used in several ways depending
on the complexity of the sequence, from manual
marking with position proposal to fully automatic
tracking with an error list indicating the uncertain
areas in the sequence. The tracking algorithm uses a
modified correlation technique and
23 Analysis
Point positions from the tracking session are used to
perform calculations of distance, velocity,
acceleration, angles and angular velocities. Other
features are:
Result presentation with graphical overlay on
the image sequence
Data and result filtering
Comparison with previous evaluations
Image and result data base
Report and documentation generation
The new module for the 3D calculations were to be a
part of the analysis software package. Since an
existing data structure was present, the module had
to fit into that environment. It turned out to be
rather complicated to do this, and the time schedule
for that part of the work were heavily under-
estimated.
3. CHOOSING AN APPROACH
The main choice was to decide which type of basic
mathematical model to use, either projective
geometry, leading to the direct linear solution, DLT,
or the collinearity equations, leading to the bundle
adjustment solution. The given conditions can be
describred as:
Accuracy requirements: + 10 mm
2 - 6 high speed cine film cameras
No fixed camera positions between sequences
No fiducial marks in camera
No fixed focus cameras
Zoom lenses may be used
Unstable inner orientation during a sequence
Several of the above mentioned conditions were
pointing toward the DLT solution, but the need of
corrections for radial distorsion and scale differences
in x and y and the fact that the inner orientation
might change during a sequence made the bundle
adjustment more attractive. If a change were detected
during the sequence, a correction of the inner and
outer orientation parameters would require less
control points to compute with a self-calibration in
the bundle adjustment than using the DLT. As a
consequence of this, the bundle adjustment approach
was chosen, giving a good structure for a self-
diagnosting system with as little operator support as
possible. The GENTRI (Larsson) soft-ware was used
for the bundle adjustment and self-calibration.
One of the major disadvantages of the chosen
appoach is the need of approximate values for the
camera orientations.
For a comprehensive comparison between the DLT
and bundle approach see (Edgardh, 1992)
4. IMPLEMENTATION
4.1 Overall view
The complete system for the 3D measuring can be
divided into two main parts: point measurements
and calculations. The point measurements is done
automatically by a tracing algorithm from one image
to the next. This part of the system will not be
discussed here but is well documented in other
sources (ref ). The mathematical (or photo-
grammetrical) part must interact with the point
measurements with a high flexibility to be able to
meet the level of automation. The three main parts
of the calculations, calibration, bundle adjustment
with self calibration and 3D measurements, must for
this reason be able to adjust themselves to the needs
at the different stages in the procedure.
Normally a sequence of images, taken with the speed
1000 frames/seconds, is calculated sequentially and
the information regarding orientation and calibration
is brought along and used if relevant. As can be seen
in fig 4 the different actions taken by the system will
be guided by the stability and functionality of the
calibrated camera parameters. If the inner orientation
parameters are stable, then the calculations can be
done with a prior calibration of a known test-field
and no additional self calibration is necessary. If the