Data Hacking

If the GPS time is early, then a negative value is used.
If the GPS time is late, then a positive value is used.
Chapter 10 — More Data Tricks
The GPS Time Fix-up Delay should be set to 0 if the Use Hardware 1PPS option is
enabled.
The final set of features on the Time tab is GPS Time Lock. NMEATime enables you to change
the criteria that the software considers for a good GPS signal lock. There are two customizable
parameters:
The GPS Quality is good (GPGGA) option is directly related to the GPGGA NMEA
message. If the GPS Quality indicator from the GPGGA sentence contains any information
(that is, it is nonzero), it is considered to be good. If the GPS receiver does not
support the GPGGA sentence, then this check box should be unchecked.
Tracking multiple satellites can also be very important. In locations such as urban areas
where sky visibility is low because of large buildings blocking the sky, it might be a good
idea to have the GPS receiver track multiple satellites before considering the signal, and
thus the time, before accepting a signal. For a good, reliable time signal, I recommend
that you consider three satellites as the minimum for a good signal lock.
Other settings come into play within the Properties dialog box too. Click the System
Configuration tab (see Figure 10-29) and make sure that Set PC Clock Using GPS is
checked.
FIGURE 10-29: NMEATime system configuration options
Now click the Update PC Clock tab (see Figure 10-30). Here you can set the update interval
for the PC clock. For systems on which you want very accurate time information, you might
want to update the clock every 1–10 minutes, whereas for lower accuracy needs you could drop
that to twice a day (an interval of 720 minutes). The maximum possible interval is 31 days
(44,640 minutes).
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