4.5. Session Definition
Field crews should attempt to simultaneously start and end observations on the user marks in the survey network in order to form GNSS sessions for processing in OP. The Session Definition, as shown in Fig. 4.7, provides some control over how OP groups near-simultaneous data files together for processing. See Appendix A for more details on how OP arranged observation files into sessions. Typically, the default values work well and do not need to be changed. However, if OP does not group the data files according to the survey plan, then these values can be changed prior to session processing. After processing begins, the values are disabled (grayed out). Session processing must be deleted to re-enable modifying these settings.
Fig. 4.7 Session Definition
Minimum Data Duration:
The Minimum Data Duration default setting is 1800 seconds (30 minutes). Since OP currently requires that all static data files are at least 7200 seconds (2 hours) in duration, then this default setting ensures that OP will in fact consider all uploaded static data as part of a session. Changing the Minimum Data Duration to something larger than 7200 seconds will instruct OP to filter data to meet that requirement. For example, if it were set to 10,800 seconds, then only static data files at least 3 hours in duration will be considered.
Minimum Session Overlap Multiplier:
The Minimum Session Overlap Multiplier helps OP arrange observations into different sessions. The multiplier instructs OP on the least allowable overlap for any pair of simultaneous GNSS observations in a session. For a pair of GNSS observations to be considered in a session, the overlap in time must be more than the product of this multiplier and the duration of the shortest observation. For example, consider two observations where one starts at 10:00 and ends at 12:00 and another starts at 11:00 and ends at 13:10. If the multiplier was set to 0.5, and since the shortest occupation is two hours, then the minimum session overlap is one hour. These two observations overlap by one hour (from 11:00 to 12:00) so they would be grouped together in a session. Before considering changing the default values, verify whether or not OP has correctly binned your observations into sessions that make sense for your project. If sessions are changed using the multiplier after session processing has occurred, the sessions will be automatically deleted. For more information on how OP groups observation data into sessions is given in Appendix B.