gpx-ideas

GPX Extensions - Position / Velocity / Time (PVT)

Overview

Position / velocity / time (PVT) elements are outputs of GPS / GNSS chipsets and location APIs.

COG and SOG are relevant to almost all activities; land, sea or air.

Name Values Description
<cog> 0 to 360 Course over ground (COG) in degrees is the actual direction of travel relative to true north. COG is an independent measurement from position, so it is possible (and not an error) for the difference between two successive positions to be inconsistent with the COG values. See RMC and VTG in NMEA 0183
<sog> >= 0 Speed over ground (SOG) / ground speed (GS) in m/s is the instantaneous horizontal speed. SOG is an independent measurement from position, so it is possible (and not an error) for the difference between two successive positions to be inconsistent with the SOG values. Speed may be measured by a wheel odometer, thus it can be independent of the GPS / GNSS receiver. See RMC and VTG in NMEA 0183 - units are knots or km/h so need to convert to m/s
<roc>   Rate of climb (ROC) / vertical speed in m/s calculated by the GPS / GNSS chipset. ROC is an independent measurement from position, so it is possible (and not an error) for the difference between two successive positions to be inconsistent with the ROC values. ROC may be measured using barometric pressure or an IMU, thus it can be independent of the GPS / GNSS receiver.
<dist> >= 0 Cumulative distance over ground for the trip / activity in meters (m). Distance may be determined by integrating speed over time or measured by a wheel odometer, thus it can be independent of the GPS / GNSS receiver. See VLW in NMEA 0183 - units are nautical miles so need to convert to meters

Accuracy estimates for COG, SOG and ROC (typically determined by the GPS / GNSS chipset) are supported by the “acc” attribute.

Name Values Description
<cog acc="n"> 0 to 180 Course over ground (COG) accuracy / error estimate in degrees, such that the difference between the true COG and the reported COG 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.
<sog acc="n"> >= 0 Speed over ground (SOG) accuracy / error estimate in m/s, such that the difference between the true SOG and the reported SOG 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.
<roc acc="n"> >= 0 Vertical speed accuracy / error estimate in m/s, such that the difference between the true ROC and the reported ROC 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.

GPX 1.2 is also expected to support position and time accuracy estimates using the “acc” attribute.

Name Values Description
<trkpt acc="n"> >= 0 Horizontal accuracy / error estimate in meters, such that the difference between the true horizontal position and the reported horizontal position 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.
<rtept acc="n"> >= 0 Horizontal accuracy / error estimate in meters, such that the difference between the true horizontal position and the reported horizontal position 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.
<wpt acc="n"> >= 0 Horizontal accuracy / error estimate in meters, such that the difference between the true horizontal position and the reported horizontal position 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.
<ele acc="n"> >= 0 Vertical accuracy / error estimate in meters, such that the difference between the true vertical position and the reported vertical position 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.
TODO - list NMEA sentences
<time acc="n">   Time accuracy / error estimate in seconds (including milliseconds), such that the difference between the true time and the reported time 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

Exclusions

Example Usage

Land / Fitness

Sea / Nautical

Air / Aviation

Meteorology