Time to first fix (TTFF) describes the time and process required to devices gps, to receive enough satellite signals to provide accurate navigational information. The word «fix» here means «position».
TTFF can affect a variety of conditions, including the environment and whether the GPS device is inside or outside. GPS navigators should be substantially free of obstructions between the device’s antenna and orbiting satellites.
The GPS must have three sets of data to provide an accurate location: GPS satellite signals, data almanac and ephemeris data.
There are generally three categories into which TTFF is divided:
- A «cold» or «factory» start refers to a situation in which the GPS device must receive all the data in order to begin navigation, for example, if the device is brand new or has recently been reset to factory settings . TTFF may take up to 12 minutes.
- A «warm» or «normal» start means the GPS keeps most of the data it needs in its memory and for a minute or less. A hot start occurs when the device has been turned off for a day or so, but not turned off for so long that the data is out of date.
- «Hot» or «standby» is when the GPS device can quickly acquire a signal because it already has a valid position and correct almanac and ephemeris data. The device was usually switched off for only a few hours. TTFF in this situation is sometimes referred to as Time to Subsequent Correction (TTSF).
More on TTFF
If the GPS device is new, has been turned off for a long period of time, or has been moved a long distance since it was last turned on, it will take longer to get these datasets and get time before the first fix. This is because the GPS data is outdated and needs to be loaded with up-to-date information.