Tech Briefs Magazine - May 2022 - PIT-12

TECHNOLOGY LEADERS Test & Measurement Systems
Determining Dynamic Object Tracking Accuracy
Measured Bar Length - Static vs Dynamic Test
here is already a wide body of
work in which assessments of varThe
nature of optical motion capture
systems means that there is a large range
of variables, making answering questions
about accuracy complicated, and some of
the most important factors in system performance
are also unintuitive. Conditions
affecting data quality can include: the size
of the space, the geometry and speed of
the object, the nature of the movement,
and changes in ambient conditions - as
well as the characteristics of the system itself
- such as the number, resolution, and
quality of cameras; the quality and size of
markers used; the camera calibration process;
and the algorithms used to compute
the rigid object pose from the camera data.
Even with a completely controlled
environment, the motion of objects can
affect the measurements. For example,
we can continuously observe the length
of a test object. It's possible to observe a
highly significant difference, depending
on whether the object is at rest or in motion.
This shows how crucial consistency
and control of the variables are before
comparisons can be made.
Terminology can often mean different
things in different contexts, with terms
such as 'accuracy' and 'precision' taking on
very different meanings. In addition to this,
they are often case-specific: for example,
the meaning of the term 'accuracy' may
321.5
321.3
321.1
320.9
320.7
320.5
320.3
T
ious motion capture systems have
produced a wide range of different
results. These studies produce useful
and relevant results for specific use cases,
but they frequently measure different
things and the methods, or even the terminology
that is used, vary significantly
in several important ways.
Static
Dynamic Object
Bar Length
Reference Length
Mean (mm) Max Error
(mm)
Static Object
Dynamic Object
320.875
320.979
0.035
0.397
be understood differently in the study of
biomechanics to robotics to visual effects.
As part of this work, we really wanted
to provide information that would be informative
and help engineers understand
what level of performance they could expect.
This demanded a method that was
appropriate to the audience that most
frequently asked about this topic, was easily
explainable, and produced sensible results
across a range of different uses.
Calculated Bar Length (mm)
322.0
321.5
321.0
320.5
320.0
3.0
2.5
2.0
1.5
1.0
0.5
0.0
320.0
Test Object as described in ASTM E3064
12
320.5
321.0
Calculated Bar Length (mm)
Single trial results for a representative high-end volume
Photonics & Imaging Technology, May 2022
321.0
1000
20000
Histogram
Frame Number
30000
Measure Length
Reference Value
Mean Measurement
RMSE (mwm) Std Dev
(mm)
0.007
0.142
Single capture showing difference between measurement of a static and dynamic object.
We also wanted to start a conversation -
internally during development, as well as
externally - with a method that was understood,
so that future developments and
improvements could be communicated in
that context. We felt it was important to
use an externally published method, to be
fully transparent about that method and
therefore about what results are achieved.
Vicon pulled together a group, led by
then Engineering Product Manager Tim
Trial Data Filename: Final DataV16\250220220Cal_02.csv
Mean Observed Bar Length: 320.897
Accuracy of Mean to Reference Length: 0.017
Standard Deviation of Observations: 0.183
Calculated Bar Length (mm)
2000
1000
-1000
-2000
-4000
40000
Reference Value
Mean Measurement
2000
1000
-1000
-2000
-4000
322.0
-2000
2000
X Dimension of Volume
4000
-2000
2000
X Dimension of Volume
Error vs Reference Length (mm)
http://info.hotims.com/82321-809
Tech Briefs Magazine - May 2022

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