trails/openspec/specs/elevation-computation/spec.md

elevation-computation Specification

Purpose

Noise-robust elevation stats in @trails-cool/gpx. Real GPS/barometric traces jitter a few metres per point and carry occasional single-point spikes, so naively summing every positive delta overstated ascent by 20–50% and distorted the profile chart. Elevation is despiked (isolated opposite-sign slope outliers interpolated out, per segment) and ascent/descent accumulate via hysteresis above a noise threshold, with the same cleaned data feeding the headline totals, the profile chart, and per-day splits so they always agree.

Requirements

Requirement: Elevation spike removal

The GPX package SHALL remove single-point elevation spikes before computing elevation totals or the elevation profile series. A point is a spike when the slopes to both its neighbors exceed the maximum-slope constant and have opposite signs; spike elevations SHALL be replaced by linear interpolation between the neighboring points. Track segment boundaries SHALL NOT be interpolated across.

Scenario: Isolated spike is interpolated out

• WHEN a track contains a point whose elevation jumps 30 m above both neighbors over a few metres of distance
• THEN the computed series replaces that point's elevation with the interpolation of its neighbors
• AND ascent/descent totals do not include the spike

Scenario: Steep but real climb is preserved

• WHEN a track climbs steeply and monotonically (successive slopes share the same sign)
• THEN no point on the climb is altered

Scenario: No interpolation across segment gaps

• WHEN a spike-like pattern spans the boundary between two track segments
• THEN points are not interpolated across the segment boundary

Requirement: Threshold-filtered ascent and descent totals

The GPX package SHALL compute ascent and descent using hysteresis accumulation: elevation change is accumulated only when altitude deviates from a moving reference by more than the noise-threshold constant. Both raw (unfiltered) and filtered totals SHALL be computed; the reported gain/loss SHALL be the filtered values, except when both filtered totals are zero and raw totals are non-zero, in which case the raw values SHALL be reported. Raw totals SHALL remain available to callers alongside the reported values.

Scenario: Jitter does not inflate ascent

• WHEN a track's elevation oscillates by ±2 m around a constant altitude over many points
• THEN the reported ascent and descent are 0 m

Scenario: Real climbs are fully counted

• WHEN a track climbs 400 m, descends 100 m, and climbs 200 m, each leg exceeding the noise threshold
• THEN the reported ascent is approximately 600 m and descent approximately 100 m

Scenario: Near-flat track falls back to raw totals

• WHEN every elevation variation in a track is below the noise threshold so filtered totals are zero
• THEN the raw totals are reported instead of 0 m

Requirement: Consistent cleaned data across totals, series, and per-day stats

The elevation profile series, the ascent/descent totals, and the per-day elevation statistics SHALL all be derived from the same despiked elevation data, and per-day ascent/descent SHALL use the same filtered accumulation such that the per-day values sum to the whole-track totals.

Scenario: Chart and headline stats agree

• WHEN a GPX with elevation spikes is parsed and rendered on a detail page
• THEN the elevation chart and the ascent/descent stats reflect the same despiked data

Scenario: Day totals sum to route total

• WHEN a multi-day route with day breaks is processed
• THEN the sum of per-day ascent values equals the route's total ascent

Requirement: Unchanged public data shape

The elevation hardening SHALL NOT change the existing GpxData["elevation"] fields (gain, loss, profile) or the ElevationSample series shape consumed by the apps; raw totals SHALL be exposed as additional fields only.

Scenario: Existing consumers compile and run unchanged

• WHEN the journal save path and detail loaders run against the updated package
• THEN they persist and render gain/loss and the elevation series without code changes