Velocity File

The generic Velocity file is used to input an external velocity that can be fused with the IMU data. This external velocity can be computed from an external equipment such as Lidar, Vision, etc.

For correct operation, the velocity data has to be accurately time stamped to an absolute timing.

Conventions

Qinertia expects the velocity data to comply with Qinertia coordinate frame and rotations directions as described in the Conventions page.

Velocity is expressed in m.s^-1 in the vehicle (X, Y, Z) reference frame

ASCII Velocity Format

This is the easiest way to input an external trajectory using a CSV like text file format.

The file format is composed of an optional header followed by Velocity data stored line by line. If Qinertia doesn't find the header, the default configuration values are used. The file can use either Windows, Unix or Linux line ending conventions and should use UTF-8 encoding.

ASCII header

The header is used to configure how Qinertia should parse and import the file. The header always starts with the $qvel magic keyword to identify it. Then each parameter can be set using a succession of <param>:<value> pairs stored line by line.

If there is no header or the parameter is not present in the file, Qinertia will use the default value that is indicated in bold.

Param	Optional	Description
`$version`		Velocity ASCII file format version, should be set to 1
`$timeSource`		Velocity data time stamp format: `gps`: Seconds from 6 January 1980 (no leap second) `gpsTow`: GPS time of week in seconds `utcIso`: ISO 6801 (e.g. 2020-06-19T11:50:04.535Z) `unix`: Seconds from 1 January 1970 (UTC time) The default value is `gps`
`$gpsWeekNumber`		GPS week number to use in case `$timeSource` is `gpsTow` If `gpsTow` is selected this parameter is mandatory and has no default value.
`$hasVelocityX`		Indicates whether or not X Velocity is available in records. The default value is `true`
`$hasVelocityY`		Indicates whether or not Y Velocity is available in records. The default value is `true`
`$hasVelocityZ`		Indicates whether or not Z Velocity is available in records. The default value is `true`
`$hasVelocityStdDev`		Indicates whether or not Velocity Std Dev. is available in records. The default value is `true`

ASCII data

The ASCII Velocity data part is a succession of time stamped position and velocity measurement stored line per line. Each column field is separated by a tabulation '\t' or semicolon ';' character.

Field	Type	Unit	Description
`timestamp`	-	-	The velocity data time stamp expressed in the format specified by the `$timeSource` header field.
`velocityX`	double	m.s^-1	X velocity, available if hasVelocityX is set to `true`, at least 4 digits required
`velocityY`	double	m.s^-1	X velocity, available if hasVelocityY is set to `true,` at least 4 digits required
`velocityZ`	double	m.s^-1	X velocity, available if hasVelocityZ is set to `true,` at least 4 digits required
`velocityStdN`	double	m.s^-1	1σ estimated X accuracy, available if hasVelocityX is set to `true` and hasVelocityStdDev is set to `true`
`velocityStdE`	double	m.s^-1	1σ estimated Y accuracy, available if hasVelocityY is set to `true` and hasVelocityStdDev is set to `true`
`velocityStdD`	double	m.s^-1	1σ estimated Z accuracy, available if hasVelocityZ is set to `true` and hasVelocityStdDev is set to `true`

Example

The example below shows a few Velocity measurements with the file header:

$qvel
$version:1
$timeSource:utcIso
$hasVelocityX:true
$hasVelocityY:true
$hasVelocityZ:true
$hasVelocityStdDev:true
2023-10-04T07:22:41.000	-1.697	1.494	0.005	-0.032	-0.032	-0.032
2023-10-04T07:22:43.000	-1.874	1.483	0.015	-0.062	-0.062	-0.062
2023-10-04T07:22:45.000	-1.848	1.451	0.019	0.044	0.044	0.044
2023-10-04T07:22:47.000	-1.889	1.449	0.060	0.010	0.010	0.010
2023-10-04T07:22:49.000	-1.932	1.607	-0.036	-0.044	-0.044	-0.044
2023-10-04T07:22:51.000	-1.738	1.435	-0.102	-0.018	-0.018	-0.018

TEXT

Binary Velocity Format

For now, there is no binary file format for the Velocity input.

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