physical_change

Measure historical physical change between two dates. Given a real polygon and two LiDAR epochs, the same unmodified function computes volume change with honest uncertainty, coverage, and full evidence — validated on 4 independent real sites across 2 countries, never reinterpreted after seeing results (success/failure criteria were frozen before running any site).

Input / output

Input

A real polygon (asset boundary)
Epoch A: a LiDAR source + nominal date
Epoch B: a second LiDAR source + nominal date
Whether the dates are independently verified (e.g. by GPS time embedded in the points, not just the filename)

Output

volume_change_m3 ± uncertainty_m3
usable_coverage_pct, n_stable_control_cells
stable_control_offset_m / sigma_m (calibration ring)
classification (never forced — can come back inconclusive)
evidence_refs — real point counts, runtimes, source files

4 validated sites — real numbers, no cherry-picking

Success/failure thresholds (coverage ≥50%, ≥200 stable control cells, σ≤1.0m, |offset|≤2.0m) were frozen before any site was run. A 5th site (Pasco County, FL) genuinely failed — 0 points returned across multiple real bounding boxes — and was recorded as a failure, not retried into a pass.

Site	Real dates	Coverage	σ control	Detection threshold	Result ± uncertainty	Ratio	Pass?
Ca na Putxa (Baleares, Spain)	2019-11-25 → 2024-04-16 (GPS-time confirmed)	83.5%	0.3124 m	0.937 m	+310,357.2 ± 182.9 m³	0.0006	YES
Leon County, FL (USA)	2009 → 2018 (official USGS project names)	98.6%	0.3463 m	1.039 m	+87,954.6 ± 119.7 m³	0.0014	YES
Orchard Ridge RDF, WI (USA)	2006 → 2017 (official USGS project names)	99.4%	0.5325 m	1.598 m	+226,719.8 ± 194.9 m³	0.0009	YES
Vertedero de Alicante (Spain, mainland)	2009 (Aug–Dec) → 2016–17 (Aug–Mar), official campaign window	89.0%	0.1544 m	0.463 m	+1,091,709.8 ± 181.8 m³	0.0002	YES

4/4 sites — 2 countries (Spain, USA), 3 climates (Mediterranean, subtropical Florida, glacial Wisconsin) — same measure_physical_change() function, zero site-specific code branches. Magnitudes are not compared against any declared capacity figure here — that cross-check is a separate, source-specific analysis (MITECO/PRTR for Spain, LMOP for the US sites), not yet completed for all 4.

Methodology

Stable-terrain calibration ring (15–350m from the polygon edge) gives a robust offset + sigma (median + MAD) between the two epochs. Detection threshold = 3×sigma. Per-cell height difference below threshold is not counted as change. Volume = sum of significant cells × cell area. Classification is NO_SIGNIFICANT_CHANGE_DETECTED if the change is smaller than its own uncertainty, AMBIGUOUS_MAGNITUDE (hard fail, never reinterpreted) if the ratio is too close to call, or DECISION_USEFUL_CHANGE_DETECTED otherwise — exactly what all 4 sites above returned.

Status

Method validated 4/4. Not offered as a paid on-demand service — gate_unblocks_deployment stays false permanently for this capability regardless of validation results; that's a deliberate, separate business decision, not a technical limitation.

Request access

If you have a specific asset and two real LiDAR epochs you'd want measured, leave your email — this tells us whether to build beyond these 4 validation sites.