gpx-smoother

README

gpx-smoother

A simple approach to smooth a GPX track without loosing too much accuracy.

Result

Usage

usage: GPX smoother [<flags>] <file>

Soe for example: gpx-smoother -d -s 10 -w 6 2019-09-19_12-12-16_new.gpx

Parameter

Detailed information with flag -h, --help.

parameter	default	description
-w, --weight	3.0	Specifies how strong the smoothing should happen. Larger numbers result in a more precise track, lower numbers in a smoother one
-s, --size	6	Specifies how much surrounding point of each GPX-point should be considered. Larger numbers result in a more precise track, lower numbers in a smoother one
-d, --debug	(not set)	Verbose mode, showing additional debug information
-h, --help	(not set)	Shows information about the usage

What parameter to choose

It depends on the density of the track points.

For tracks with points every 5 meter the default parameters (-w 3 -s 6) are fine. For dense tracks a larger size-value (e.g. -s 10) might be better.

Algorithm

Currently this takes each point of the track and gets n neighbors around it. Then a weighted average of their locations is calculated: Points near by are weighted more than points far away.

 // Basically: How strong is the weight. This is later an exponent.
weightFactor := 3.0

// for each point:

	// for each neighbor of the current point

		// Weight look like: 1 2 3 [4] 3 2 1 (where [4] is the point currently looking at)
		// This is used as basis for "weight^weightFactor"
		weight := stepsBackwards/2 - int(math.Abs(float64(j-i))) + 1

		// sum up the coordinates
		latSum += points[j].Lat * math.Pow(float64(weight), weightFactor)
		lonSum += points[j].Lon * math.Pow(float64(weight), weightFactor)

	// To later get the correct location, we need to know how many locations we used
	weightSum += math.Pow(float64(weight), weightFactor)

// Get the average
newTrkpt[i-stepsBackwards/2] = Trkpt{
	Lat: latSum / weightSum,
	Lon: lonSum / weightSum,
}