Advanced Operation
35
Advanced Operation
Closed-Loop Technique (Advanced Trigger)
The closed-loop technique combines PPS synchronization and shutter timing as
shown in Figure 4.9.
In this technique, the 1PPS output of the GG Surveyor triggers a camera shutter. The
camera shutter generates a signal that is fed to the GG Surveyor for accurate time
tagging.
The delay between the camera receiving the pulse and triggering the photogrammetry
port should be calculated. This may then be applied so as to advance the 1PPS from
the GG Surveyor so that the shutter time exactly matches the GPS system time for the
epoch. No interpolation between the shutter time and the GPS position time will be
needed.
Data Output
Real time data output is only available through the three RS-232 ports. Refer to
“NMEA Data Message Commands” on page 129 and “Raw Data Commands” on
page 115 for more details. There are three types of messages:
•
NMEA
NMEA is a standard data transfer format developed to permit ready and
satisfactory data communication between electronic marine instruments,
navigation equipment and communications equipment when interconnected
via an appropriate system. This is data in printable ASCII format and may
include information such as position, speed, frequency allocation, etc.
Figure 4.9: Closed Loop Technique
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