What is the GPS accuracy and how is this calculated?
The location of the Spider is determined by a U-Blox GPS antenna and module inside the hardware. This calculates the the position via the GPS network every second. When a position report is to be sent it will use the latest location information for that position report.
The Spider GPS altitude is Above Mean Sea Level (AMSL). This means you may see a difference between pressure altitude sensors or Above Ground Level (AGL) altitude sensors. The vertical accuracy is approximately within 100 feet. This is in ideal conditions and depends on where the Spider is in relation to the satellites therefore actual position may be affected.
The GPS module reports a Horizontal Dilution of Position (HDOP) value that is an accuracy estimation of the horizontal position. The Spider does not send a position report with an HDOP value of more than 8. The horizontal accuracy is approximately within 10 feet. This is in ideal conditions and depends on where the Spider is in relation to the satellites therefore actual position may be affected.
GPS Altitude vs Barometric Altitude
The barometric altimeter calculates pressure altitude based upon the atmospheric pressure setting applied to the aircraft’s altimeter (QNH/QFE).
- GPS altitude a geometrical calculation.
- Barometric altitude a pressure related calculation.