Changes between Version 1 and Version 2 of Sensors/Hawk

Timestamp:

Feb 14, 2012, 12:10:03 PM (13 years ago)

Author:

mark1

Comment:

--

Sensors/Hawk

@@ -10 +10 @@
 
 The .nav files are a collection of different 'messages'. These contain the real-time position and attitude of the aircraft as well as periodic time stamps marking the start of the flight line capture.
+
+=== Timing ===
+
+The Eagle instrument is connected to a nav-sync box that timestamps the start of acquisition against GPS time.  This measures the time to the next GPS pulse-per-second, from the first start of integration pulse from the camera that occurs after the start of acquisition pulse from the recording system.
+
+The frame grabber lag time is unknown.  Previously it was thought to be 55ms regardless of frame rate (i.e. a frame is captured 55ms before the nav sync pulse), but this was actually a once-off correction applied by Specim for a single dataset.  What was called the frame grabber lag time is actually an unknown timing error in the system.  Further work is underway to isolate this.
+
+Consequently the timing of a start of acquisition is `next_GPS_PPS - navsync_time - <unknown and variable error>ms`.
 
 == Specifications ==