gps-wizard

Data Fields

The table below provides a summary of the data fields populated by the GPS Wizard file readers.

Detailed field mappings and precision / resolution are available via the hyperlinks in the table header.

Name	Description	Type	Units	FIT	GPX	NMEA	SPB	SBN	OAO	UBX
cog	course over ground	float32	deg	Yes 1	Yes 2	Yes	Yes	Yes	Yes	Yes
cogu	course over ground (unfiltered)	float32	deg	-	-	-	-	Yes	-	-
dist	cumulative distance	float64	m	Yes	-	-	-	-	-	-
ece	estimated course error	float32	deg	-	-	-	-	-	Yes	Yes
ehpe	estimated horizontal positional error	float32	m	-	-	-	Yes	Yes	Yes	Yes
ehve	estimated horizontal velocity error	float32	m/s	-	-	-	Yes	Yes	Yes	Yes
ele	elevation above mean sea level	float64	m	Yes 3	Yes	Yes	Yes	Yes	Yes	Yes
evpe	estimated vertical positional error	float32	m	-	-	-	Yes	Yes	Yes	Yes
evve	estimated vertical velocity error	float32	m/s	-	-	-	Yes	Yes	-	-
fix	fix type - ublox	uint8	-	-	-	-	-	-	Yes	Yes
hdop	horizontal dilution of precision	float32	-	Yes 1	Yes 2	Yes	Yes	Yes	Yes 4	-
lat	latitude	float64	deg	Yes	Yes	Yes	Yes	Yes	Yes	Yes
lon	longitude	float64	deg	Yes	Yes	Yes	Yes	Yes	Yes	Yes
pdop	positional dilution of precision	float32	-	-	-	-	-	-	Yes 4	Yes
roc	rate of climb	float32	m/s	Yes 5	-	-	Yes	Yes	-	Yes
sat	satellites	uint8	-	Yes 1	Yes 2	Yes	Yes	Yes	Yes	Yes
sog	speed over ground	float32	m/s	Yes	Yes 2	Yes	Yes	Yes	Yes	Yes
sogu	speed over ground (unfiltered)	float32	m/s	-	-	-	-	Yes	-	-
svids	space vehicle / satellite IDs	uint32	-	-	-	-	Yes	Yes	-	-
ts	timestamp - since 1 Jan 1970	float64	s	Yes	Yes	Yes	Yes	Yes	Yes	Yes

Notes:

1. COG (cog), Satellites (Sat) and HDOP (hdop) are only present in COROS FIT files.
2. COG (course), Satellites (sat), HDOP (hdop) and SOG (speed) are typically absent in GPX files.
3. Elevation (altitude) is currently absent in COROS FIT files; May 2022.
4. OAO files produced by the ESP-GPS record PDOP in the HDOP field.
5. ROC (vertical_speed) is only present in Suunto FIT files.

Data Types

Careful consideration has been given to the data type of each field:

1. Single and double precision floats (float32 and float64) have been used where applicable.
2. Half precision floats (float16) are avoided because they are often unimplemented at a hardware level, thus can be slow.
3. Integers were also considered (e.g. units of mm or mm/s) but single and double precision floats were chosen in preference.

Elevation

During the testing of the GPS Wizard modules, it was observed that GPSResults uses “altitude from ellipsoid” instead of “altitude from MSL”, when loading SBN files.

Since the SBP format only includes “altitude from MSL”, corresponding SBN and SBP files from the same session will show different altitudes in GPSResults.

GPS Wizard uses “altitude from MSL” as standard, since it is available in all supported file formats; FIT, GPX, NMEA, SBN, SBP, OAO and UBX.

In contrast, “altitude from ellipsoid” is only available in the SBN and UBX formats and is unavailable in FIT, GPX, NMEA, SBP and OAO.

TODO

Tweaks:

• Populate fix type for more formats - e.g. SBN, GPX, NMEA

Field additions / derivations:

• latr, lonr (float64) - radians.
• secs (float32) - time difference in seconds.
• cogp, sogp, rocp (float32) - derived from positional data.
• dist and distp (float64) - calculated from sog and sogp.

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