8. PROCESSING RESULTS
x
z
(optical axis)
y
Camera
Figure 11: Coordinate system used for 3D reconstruction.
disparities and mark them as invalid. Invalid disparities are set to 0xFFF,
which is the highest value that can be stored in a 12-bit disparity map. In
the example disparity map from Figure 10b, invalid disparities are depicted as
black.
Please note that there is a stripe of invalid disparities on the left image
border of the example disparity map. This behavior is expected as the disparity
map is computed from the perspective of the left camera. Image regions on
the left edge of the left camera image cannot be observed by the right camera,
and therefore no valid disparity can be computed. The farther left an object
is located, the farther away it has to be, in order to also be visible to the right
camera. The full depth range can only be observed for left image pixels with
a horizontal image coordinate
u
≥
d
max
.
8.3 Timestamps and Sequence Numbers
Each pair of rectied left camera image and disparity map, which is trans-
mitted by SceneScan, also includes a timestamp and a sequence number. The
timestamp is measured with microsecond accuracy and is set to either the time
at which a camera trigger signal was generated or the time at which a frame
was received from the cameras (see Section 9.7). For images that are received
over the network, as described in Section 7.6, the timestamp and the sequence
number are both copied.
As explained in Sections 7.8 and 9.8, it is possible to synchronize Scene-
Scan's internal clock to an external signal or a time server. This directly aects
the produced time stamps. When synchronized to a time server, time stamps
are measured in microseconds since 1 January 1970, 00:00:00 UTC. If no syn-
chronization is performed, the internal clock is set to 1 January 2017, 00:00:00
UTC at the time SceneScan is powered up. If synchronizing to an external
signal, the clock is set to 0 at the rising edge of the synchronization signal.
Please note that synchronizing to a PPS signal, as explained in Section 7.8,
also produces negative timestamps. Depending on the selected timestamp
source, this happens when a synchronization signal is received while SceneScan
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