# Ohmforge GPS Trip Stats (GPX → speed and distance)

> GPX track in: distance, moving time, average and maximum speed, climb and km splits. Reads a GPX track from a bike computer, sports watch, phone app or Ohmforge's Pocket instruments speedometer and works out the trip: distance along the WGS84 ellipsoid, total, moving and stopped time, average, moving-average and maximum speed, elevation gain and loss, a speed profile and per-kilometre splits. Speeds come from positions and times, so jittery GPS points do not inflate the maximum.

Part of usefulweb.app (https://usefulweb.app/). Part of [Ohmforge](https://ohmforge.usefulweb.app/) (ownerApp: ohmforge). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ohmforgegpstripstats.usefulweb.app/ (interactive tool at https://ohmforgegpstripstats.usefulweb.app/tool)
- JSON API: POST https://ohmforgegpstripstats.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://ohmforgegpstripstats.usefulweb.app/api/v1/tool)
- OpenAPI: https://ohmforgegpstripstats.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://ohmforgegpstripstats.usefulweb.app/mcp - tool `ohmforge_gps_trip_stats`

## Inputs
- file (file): GPX file - Tracks (and routes with times); every point needs a <time>. Up to 200 000 points. Processed in memory and not kept.
- gpx (textarea): Or paste the GPX - Used when no file is uploaded.
- stopKmh (number): Counts as stopped below
- windowSeconds (number): Shortest window for the maximum speed - Speeds are averaged over at least this time; longer windows smooth out GPS jumps.
- minStep (number): Jitter filter: ignore steps shorter than - Phones standing still or walking slowly scatter around the true position and add distance. 0 = keep every point; 5–10 m suits walking with a phone.
- elevationThreshold (number): Elevation noise threshold - Ups and downs smaller than this are ignored when adding up the climb.

## Method
- Distances are geodesics on the WGS84 ellipsoid between consecutive points (Karney's algorithm, the same geodesic code as RavingDesk). The GPX file is read with RavingDesk's safe XML reader; track segments stay separate, so a pause between segments adds time but no distance.
- Points are grouped into windows that span at least the chosen number of seconds. Each window gives one speed (distance ÷ time); windows slower than the stop speed count as stopped time, the fastest full window is the maximum speed. Averages: distance ÷ total time and distance ÷ moving time.
- Elevation gain and loss count only changes larger than the noise threshold (hysteresis), because GPS heights scatter by several metres. Splits interpolate the time at each full kilometre.
- The optional jitter filter drops points that lie closer than the given distance to the last kept point (the last point of each segment always stays), which removes the zig-zag a phone records while standing or walking slowly.

## Limits
- GPS positions scatter by a few metres, more under trees and between buildings; distances and maximum speeds from a phone are estimates. Never read a phone speedometer while driving or riding.