Rewrite elevation across an activity.

Most smart trainers and indoor apps (Zwift, Wahoo SYSTM, TrainerRoad, Rouvy) either omit the altitude field entirely or write a constant zero. The result on Strava is a zero-elevation line and zero elevation gain even if the workout simulated a 1000m climb. The elevation setter's ramp mode lets you backfill a plausible altitude profile - enter starting altitude and total gain, and the tool distributes the gain across the activity by cumulative distance so the elevation chart matches what the ride felt like.

Use the terrain mode. The tool walks every trackpoint, queries Mapbox's terrain DEM tiles for the elevation at that lat/lon, and writes the result back to the altitude field. The output replaces noisy or wildly inaccurate phone GPS altitude with consistent DEM-based values accurate to within 5-10m in most terrain. Useful for runs and rides recorded on a phone where the barometric altimeter was absent or unreliable.

Mapbox terrain tiles combine SRTM (Shuttle Radar Topography Mission) and other Digital Elevation Model sources at roughly 30m horizontal resolution. Vertical accuracy is around 5-10m in non-mountainous terrain, up to 15-20m in dense forest or steep alpine. Better than phone GPS altitude (often plus-or-minus 20-50m), worse than a properly-calibrated barometric altimeter (plus-or-minus 1-3m).

Yes - the tool recomputes total ascent and descent from the new elevation profile and updates the session and lap totals to match. For trainer rides moving from flat-line to ramped, total ascent will go from 0 up to your specified gain. For phone GPS recordings being refetched against DEM, total ascent typically goes down 10-30% because phone GPS altitude noise inflates apparent climb.

Elevation directly affects any grade-derived metric (grade-adjusted pace, VAM, power-vs-grade plots) computed downstream. The HR, power, cadence, speed, lat, and lon streams are untouched. Total distance and moving time are unchanged. After rewrite, derived metrics like VAM and GAP will update on the next platform recompute - Strava recalculates on re-upload.

Ramp. Zwift rides simulate virtual routes that do not correspond to real-world terrain - refetching real DEM elevation from the GPS positions (which Zwift writes as fake coordinates near Watopia) produces nonsense. Use ramp mode and enter the total simulated climb Zwift reported as your gain target.

Use terrain refetch. The lat/lon coordinates are real, so DEM sampling produces meaningful elevation. For rides where the barometric altimeter was solid (most modern Garmin Edge and Wahoo ELEMNT units), the original altitude is probably more accurate than DEM refetch and you should leave it alone. For phone GPS recordings or rides where the altimeter clearly drifted (start altitude does not match end altitude even though you ended where you started), refetch is the fix.

Yes - the ramp mode is fully free and runs offline. Terrain mode uses Mapbox's tile API and is also free for the volume any single user generates. No signup, no upload, no upsell.