Thought I post all the numbers / specs here - instead of having them spread across the forum:
- Videos are mostly recorded at 30Hz, there are higher rates available to allow slo-mo effects; this part is not covered here
- Memory used for videos depends on the so called bitrate - the number of bits available per second of a video. For HD video, a typical bitrate is 10.5Mbit/s. Add some additional space for audio and we are at approximately 80MB/min. For FullHD video - supported by the iPhone4S and later, a typical bitrate is 24Mbit/s, summing up to approximately 190MB/min. For 4K UltraHD video - supported by the iPhone6S and later, a typical bitrate is 50Mbit/s, summing up to approximately 400MB/min.
- HD resolution on an iPhone is 1280x720, Full HD resolution is 1920x1080, and Ultra HD is 3840x2160.
- The time required to overlay compared to the original video's length depends on video resolution, phone generation, LapTimer version, and OS version. Late iPhones require less time to overlay a video than the video's length - even for FullHD (factor 0.5 to 1.0). As an example, a 20 minute session may require 10 minutes to overlay. Android smartphones supporting hardware accelerated video encoding (Android > 5.1) will require between double and four times the session's time (factor 2.0 to 4.0) while older Android phones may take up zoo a factor 20.0 (software encoding).
- This actually means LapTimer is able to overlay videos in realtime - in theory. We will see what is possible in the future... The progress in the overlaying is pretty exciting.
- Starting with v15, LapTimer is capable to record more than 4bill of GPS positions. For both 1Hz and higher update rate GPSes this means there is practically no limitation for GPS recording.
- Memory is no real limitation for data recordings, as one fix (including acceleration, OBD, everything) requires 78 bytes only. Going back to the memory per minute discussion, this means data recording requires 4.6kB/min for the internal GPS, and 23kB/min for a 5 Hz external GPS.
Timing accuracy has been improved by sophisticated interpolation technics from the beginning; in addition, both the iPhone's internal sensors, Apple's location service implementation, and LapTimer's direct integration of sensors have improved over time; check the table below to get rough numbers on timing accuracy...
- iPhone3G's and 3GS's internal GPS: better than 0.5 seconds
- iPhone4s and 4Ss internal GPS: better than 0.1 seconds
- iPhone5s seem to deliver same accuracy and update rate like the iPhone4s
- Any iPhone directly integrated with a supported external sensors (Emprum's Ultimate GPS, Dual's XGPS150, TomTom car kit, and G-Fi): around 0.05 seconds, 5 Hz device better than 0.05 seconds
- Android Smartphones allowing access to their NMEA data deliver accuracy around 0.05 seconds
The interpolation algorithms used by LapTimer generate the best possible accuracy a GPS based system can achieve. So accuracy is a function of GPS quality and nothing else. In case your requirements are not met by the above values, the only option is to use a transponder system. These will certainly deliver lap times only and completely miss data recording.
to be continued
P.S. iPhones have GPS sensors integrated in a so called RF chip featuring all kinds of net services like UMTS, LTE, etc. The iPhone5 uses a Qualcomm RTR8606 while the iPhone4S uses a Qualcomm RTR8605. The iPhone5 adds LTE cellular network support, so this is probably the change in version number. As the internal GPSes are good enough for location services as used for 'normal' iPhone users, I doubt a lot of development efforts are going into the GPS part in the future. For better performance, specialized devices will be the best choice (see Compatibility).