8. PROCESSING RESULTS
the left camera always appear before their right camera counter parts when
sorted alphabetically.
7.7 External Trigger
For stereo matching, it is important that both cameras are synchronized, mean-
ing that both cameras record an image at exactly the same point of time. Many
industrial cameras already feature the ability to synchronize themselves, by
having one camera produce a trigger signal for the respective other camera.
As an alternative, SceneScan can produce up to two trigger signals. The
signals are provided through the trigger port, which is described in Section 6.3.
The peak voltage of both trigger signals is at +3.3 V and a maximum current
of 24 mA can be supplied. The polarity of the trigger signals is active high.
For exact timing measurements, it is recommended that the cameras trigger
on the rising signal edge. The pulse width and frequency can be adjusted in
the trigger conguration (see Section 9.7).
7.8 Time Synchronization Signal
As described in Section 6.3, one pin of the trigger port is dedicated to a time
synchronization signal. If PPS time synchronization is activated in the device
conguration (see Section 9.8), the internal clock is set to 0 whenever a rising
signal edge is received on this pin. In order to trigger a synchronization, the
signal must have a voltage level of at least 0.7 V. The maximum allowed voltage
is 5.5 V.
Clock synchronization is useful when interpreting the timestamps that are
embedded in the transmitted processing results (see Section 8.3). The syn-
chronization input can be connected to the Pulse-Per-Second (PPS) output of
a GPS receiver or a precision oscillator, in which case the clock is reset once
per second. This allows for the reconstruction of high-precision timestamps on
the computer receiving SceneScan's processing results.
As an alternative to synchronizing to an external signal, SceneScan can also
perform a clock synchronization through the Network Time Protocol (NTP)
or Precision Time Protocol (PTP), as described in Section 9.8.
8 Processing Results
8.1 Rectied Images
Even when carefully aligning both cameras, you are unlikely to receive images
that match the expected result form an ideal camera geometry. The images are
aected by various distortions that result from errors in the cameras' optics
and mounting. Therefore, the rst processing step that is performed is an
image undistortion operation, which is known as image rectication.
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