User manual
Version: v4.5.2
8.4 Latency measuring
The fusionTrack latency depends on several factors, among which
- the picture size,
- the Ethernet adapter performance,
play a key role. When the picture size is too high, the transmission time impacts the latency and the
frame rate. This is the reason why the ‘Picture rejection threshold’ option has been introduced in the 3.0.1
version of the SDK. Atracsys now provides a sample which allows to tune the value of the ‘Picture rejection
threshold’ option according to the target environment and running platform:
ftk20_Latency
, available both
as a pre-compiled binary and source code.
The software acquires data at the maximal available rate. It performs several loops during which a certain
number of frames are retrieved. The following quantities are computed:
- the average time between two pictures acquisitions at the hardware level (i.e. in the fusionTrack
firmware) is computed (and compared with the hardware-set value);
- the average and maximum time between two pictures acquisitions at the host PC level (i.e. the time
between two successive calls to
ftkGetLastFrame
;
- the average and maximum difference between the hardware acquisition time (i.e. time between two
picture acquisition at the hardware level) and the software acquisition time (i.e. time between two
picture acquisition at the host PC level).
8.4.1 Running the software
The user can steer the behaviour of the software via the following options:
- number of recorded frames in each loop, set via the
-f/--nbframes M
switch;
- number of loops, set via the
-n/--nbloops N
switch;
- tolerance on the maximum time between two acquisitions at the host PC level, set via the
-u/--
maxUpdateTime T
switch;
- tolerance on the maximum difference between the hardware acquisition time and software acquisition
time, set via the
-l/--maxLatencyTime T
switch;
- maximum picture size in bytes, set via the
-s/--pictureSize S
switch.
The software is meant to be run with the fusionTrack device sending busy pictures corresponding to the
maximal picture size expected in the user application. In the case of maximal size pictures (blank), these
can be easily generated by covering both cameras with a a white sheet of paper. The picture size cutoff can
then be empirically determined once the maximum allowed latency is determined by the user. An example
of output with only 10 loops is given in Listing 8.4.
1
./ ftk20_Latency64 .exe -n 10
2
This is the Atracsys latency
test
and update rate program .
3
Copyright (c) Atracsys LLC 2018
4
Detected one with serial number 0 x400000091e566128
5
1/10: 1000 received frames among which 1000 have been ignored (size cutoff ),
0 dropped
frames ,
0 processed frames
0 missed frames
Atracsys / 2020-06-17 / 16:48:00
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