gpx-ideas

GPX Extensions - Inertial Measurement Unit

Overview

Heading (yaw) and attitude (pitch and roll) from inertial measurement units (IMUs) is relevant to a huge number of activities; land, sea and air.

Name	Values	Description
<hdg>	0 to 360	Heading (HDG) is the direction in which an object is pointed, relative to true north in degrees (°). Heading and yaw are synonymous but sailors and pilots will always refer to yaw as heading. See THS, HDT, HDG and VHW in NMEA 0183
<pitch>	-90 to +90	Pitch is the up / down rotation of an object about its transverse / y axis in degrees (°). Sailors will sometimes refer to pitch as “trim”
<roll>	-180 to +180	Roll is the side-to-side rotation of an object about its longitudinal / x axis in degrees (°). Sailors refer to roll as “heel”, whereas pilots refer to it as “bank”. A value greater than 90 degrees indicates an inversion of the vessel / aircraft.
<stat>	0 or 1	INS status flag. 0 = SPAN pre-alignment INS status, 1 = SPAN post-alignment INS status
<rot>		Rate of turn (ROT) is the rate of change of heading, measured in degrees per minute (°/min). A positive number means turning clockwise and negative number means turning counter-clockwise. ROT is most relevant to ships and aircraft where it is a measure of how fast the vessel / aircraft is turning. See ROT in NMEA 0183

Accuracy estimates for heading, roll and pitch can be provided using the “acc” attribute.

Name	Values	Description
<hdg acc="n">	0 to 180	Heading accuracy / error estimate in degrees, such that the difference between the true yaw and the reported yaw is less than the accuracy / error estimate 68% of the time. 68% corresponds to 1-sigma of a normal distribution, but this does not imply that errors are independent or normally distributed.
<roll acc="n">	0 to 180	Roll accuracy / error estimate in degrees, such that the difference between the true roll and the reported roll is less than the accuracy / error estimate 68% of the time. 68% corresponds to 1-sigma of a normal distribution, but this does not imply that errors are independent or normally distributed.
<pitch acc="n">	0 to 90	Pitch accuracy / error estimate in degrees, such that the difference between the true pitch and the reported pitch is less than the accuracy / error estimate 68% of the time. 68% corresponds to 1-sigma of a normal distribution, but this does not imply that errors are independent or normally distributed.

Notes

• The standard abbreviation for heading is HDG in nautical and aviation environments, hence the naming of <hdg> in this schema
  • The words heading and yaw are synonymous. However, yaw values are sometimes -180 to 180, so heading = (yaw + 360) % 360
  • The aviation industry (worldwide) is currently preparing to switch from magnetic north to true north - Mag2True
• The use of an optional “id” attribute (see gpx_eng) would allow for multiple IMUs (e.g. vehicle and camera) - see requirement
• The availability of accuracy / error estimates is largely due to the use of a Kalman filter within the IMU
• Rate of turn (ROT) is important on board ships and aircraft. Should it go into gpx_air and gpx_sea instead of gpx_imu?
  • It is worth noting that ROT is determined by a gyroscopic instrument, and may thus belong in gpx_imu for generic use

Exclusions

• Instantaneous heave (up / down), sway (left / right) and surge (front / back)
  • Instantaneous heave is sometimes calculated in GNSS + INS solutions, but not sway or surge?

Example Usage

Sea / Nautical

• Dinghy Racing
• Yachting

Air / Aviation

• Skydiver
• Microlight
• Light Aircraft

Meteorology

• Weather Station

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