XTF notes

Here are a few notes to help guide you through my XTF convertor programs. Slim pickins for now, but I plan on adding to this as I encounter the usual hangups that slow me down when trying to run my own software. Stay tuned and feel free to email me any suggestions.

Time synchronization

XTF packets have a millisecond time stamp that isn't always referenced to a meaningful absolute time (e.g ms since start of day, or ms since 1970). This means that all packets are relatively timed to millisecond precision, but the millisecond time stamp doesn't give an indication of the actual time. To time things absolutely, we need to know the time that corresponds to the 'zero' of the milliseconds time stamp. This is done through the establishment of what I call the 'basetime', it is done automatically through various methods, as outlined below. The algorithm that decides on the best method to use is sensitive to the sonar type (it must be able to distinguish between RESON and Simrad data). When the "sonar type" field in the XTF header is incorrect, you may have to "force" the packet synchronization method (done with -force_synch in the xtf conversion programs). The codes correspond to the options below.

Last modified by J. Beaudoin, 20080110