metrictrails

metrictrails is an R package to read, clean and standardise GNSS streams recorded by sports watches and similar devices, with a focus on trail and mountain running. It is the successor of GPStream and implements the methods of the Metric Trails research papers (see References).

A stream is any sequence of consecutive readings with lon and lat, and optionally ele, timestamp, time, heart rate, cadence and other variables.

Installation

# install.packages("remotes")
remotes::install_github("raimun2/metrictrails")

The pipeline

A full walkthrough is in the vignette: vignette("metrictrails").

step function what it does
1. ingest read_stream() reads a GPX file with sf (tracks or routes, segments and Garmin extensions)
2. naming convention uniform_stream() renames columns to lon, lat, ele, timestamp, time
3. sanitize sanitize_stream() smooths lon/lat (Kalman by default; LOESS, Gaussian kernel, Savitzky-Golay or the full ICECET 2026 pipeline) and flags implausible readings
4. resample resolution_stream(), resample_stream() resamples to a uniform 2D spatial resolution derived from the Nyquist criterion
5. elevation get_dem(), resample_dem(), ele_correction() replaces elevation with values from a Digital Elevation Model 
library(metrictrails)

f = system.file("extdata", "gpx_activity.gpx", package = "metrictrails")
dem = system.file("extdata", "test_dem.tif", package = "metrictrails")

raw = read_stream(f) %>% uniform_stream()
raw
#> # A tibble: 2,510 x 9
#>     lon   lat   ele timestamp            time segment atemp    hr   cad
#>   <dbl> <dbl> <dbl> <dttm>              <dbl>   <int> <dbl> <dbl> <dbl>
#> 1 -70.6 -33.4  772  2020-08-10 19:36:38     0       1    27   106    47
#> 2 -70.6 -33.4  771  2020-08-10 19:36:39     1       1    27   108    47
#> 3 -70.6 -33.4  772. 2020-08-10 19:36:42     4       1    27   111    76
#> # i 2,507 more rows

final = raw %>%
  sanitize_stream() %>%       # Kalman smoothing + red flags
  resample_stream() %>%       # Nyquist resolution
  ele_correction(dem = dem)   # DEM elevation (omit `dem` to download one)

Sanitize: smoothing and red flags

Flags are computed on the raw readings. Position flags (time, speed, acceleration, edge jumps) and elevation flags (slope, vertical speed, elevation change while idle) can be kept, dropped or interpolated (action).

clean = sanitize_stream(raw)
attr(clean, "sanitize_report")$counts
#>       flag_time      flag_speed      flag_accel       flag_jump      flag_slope
#>               0               0               0               0              71
#> flag_vert_speed   flag_idle_ele        flag_gap    flag_low_res
#>               3               3               0              10

Resample: the Nyquist resolution

A watch that records at a fixed rate produces a spatial resolution that is a random variable (speed times sampling interval), so distance and elevation gain depend on how fast the athlete moved. resolution_stream() describes the distribution of the 2D distance between moving readings. Its 0.9 quantile is the finest uniform spacing that represents the path without inventing readings, and resample_stream() uses it by default. To compare several streams, resample all of them with one common res.

resolution_stream(clean)
#> # A tibble: 1 x 12
#>       n pct_idle  mean    sd   q05   q25   q50   q75   q95   max     q   res
#>   <int>    <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1  2510   0.0797  2.97  3.07 0.512  1.08  2.00  3.49  9.10  22.8   0.9  6.31

Elevation from a DEM

get_dem() downloads AWS Terrain Tiles (zoom 14, about 4 m at the latitude of Santiago) for the extent of the stream and projects them to its UTM zone. resample_dem() refines the DEM by bilinear interpolation, or aggregates it.

Measures

cols = c("distance_2d", "elevation_gain", "km_effort", "resolution", "fractal_dim")
summarise_stream(raw, fractal = TRUE)[, cols]     # raw device
#> # A tibble: 1 x 5
#>   distance_2d elevation_gain km_effort resolution fractal_dim
#>         <dbl>          <dbl>     <dbl>      <dbl>       <dbl>
#> 1       7847.           889.      16.7       3.13        1.07
summarise_stream(final, fractal = TRUE)[, cols]   # after the pipeline
#> # A tibble: 1 x 5
#>   distance_2d elevation_gain km_effort resolution fractal_dim
#>         <dbl>          <dbl>     <dbl>      <dbl>       <dbl>
#> 1       7281.           951.      16.8       6.16        1.08

tobler_stream(final)   # speed-slope frontier (90th percentile)
#> # A tibble: 1 x 8
#>      v1    m1 c_plus c_minus   tau     n    r1 method
#>   <dbl> <dbl>  <dbl>   <dbl> <dbl> <int> <dbl> <chr>
#> 1  3.30 0.148   3.40 -0.0248   0.9  1083 0.236 pinball

Two-stream operations

route = read_stream(system.file("extdata", "gpx_route.gpx", package = "metrictrails"))

# predicate: does the stream follow the route, and where?
detect_stream(raw, route)
#> # A tibble: 1 x 6
#>    pass start_row end_row direction coverage status
#>   <int>     <int>   <int> <chr>        <dbl> <chr>
#> 1     1         1    2506 forward          1 match

# transformation: where was the athlete along a known reference at each time?
ref = route %>% resample_stream(res = 2) %>% ele_correction(dem = dem)
matched = match_stream(clean, ref, params = tobler_stream(final))
summary(matched$offset_d)   # distance from each reading to its matched position
#>     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
#>  0.05679  4.30900  7.17398  8.98717 11.64175 45.55705

Data

References

Use citation("metrictrails") to cite the package.

License

MIT © Raimundo Sanchez

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