Drop a pin, type a height — and read, in one column, every ceiling that governs that spot, which one bites first, and by how many feet. Federal screening and the local referral gate, in the same click.
Obstacle-surface engines are excellent — and they are licensed desktop products run by the airport's consultant, a few times per master-plan cycle. They serve the specialist.
The volume is somewhere else entirely: the developer sizing a building, the city planner at the permit counter, the crane operator, the county commission processing a referral. They ask one question, constantly — and they have no map to ask it on.
ACRP Research Report 195 tells airports to build an obstruction-management programme and share the surfaces with the surrounding land-use jurisdictions. That sharing step is where practice collapses.
The surfaces sit in a consultant's geodatabase. The permits are issued at a city counter. The airport finds out when the crane is already up.
FAA US_Airport.ELEVATION — the Part 77 datum, published for every US airport.
FAA runway geometry + its published length — which selects the 100:1, 50:1 or 25:1 notice slope.
USGS 3DEP point elevation — keyless and CORS-open, so it can be read straight from a browser.
14 CFR §77.9 needs nothing else. The FAA's own Notice Criteria Tool does this calculation — as a form, with no map, no neighbours, and no answer about the local gate. Nobody had put the arithmetic on an open map.
Every governing ceiling stacked on one feet-MSL axis, your structure drawn against them, the binding rung named.
Clear · notice required · presumed obstruction — with the margin in feet and the rule that produced it.
The county compatibility zone under the pin, its adopted rule text and plan link — or an honest "unknown".
A printable screening record: every rung, its formula, its three inputs and their sources. The deliverable.
A developer, a city planner, a commission analyst and an airport planner can all read the same screen — and the section view shows them why: the slope rising from the runway threshold, the terrain beneath it, and what is already standing in between.
San José Mineta (KSJC): airport elevation 62.3 ft MSL, longest runway 11,000 ft ⇒ the 100:1 slope applies for 20,000 ft. A site 14,000 ft out, ground 59 ft from 3DEP.
§77.9(b) allows 62.3 + 14,000 ÷ 100 = 202.3 ft MSL. At 130 ft AGL you top out at 189 — clear by 13 feet. At 320 ft you top out at 379 — a presumed obstruction by 177.
Same pin. Same formula. The number moves, and so does the answer — printed with its provenance, every time.
Sources: the FAA Aeronautical Information Services ArcGIS org (107 services — airports, runways, obstacles, class and special-use airspace, airport mapping), USGS 3DEP elevation, Caltrans Division of Aeronautics, and county compatibility-plan geometry. Everything EPSG:4326, keyless, fetched live.
This is a screening pre-check, not a determination. It computes §77.9 notice criteria, §77.17 obstruction standards and the §77.19 horizontal and conical surfaces — and hands the user to the FAA's filing portal.
A screening tool that hides its arithmetic is worse than no tool. Every rung carries its rule citation, its formula and its inputs — so the answer can be checked, argued with, and defended.
| Obstacle-surface engines | The Altimeter | |
|---|---|---|
| Who uses it | The airport's consultant, on a master-plan cycle | Developers, city counters, commission staff, airport planners — daily |
| Output | Authoritative 3D surfaces, charts, eTOD deliverables | A screening verdict, a margin in feet, and a referral packet |
| Deployment | Licensed desktop / enterprise | Open, keyless, on your servers behind your SSO |
| Data | Survey + licensed feeds | Public feeds only — verified, cited, refreshable |
An airport that already owns an obstacle-surface engine should publish its authoritative surfaces into this app — that is the ACRP recommendation, finally executable. And the same three numbers answer an ICAO Annex 14 safeguarding question, which matters as states work toward the 2030 obstacle-surface transition.
An open design — the vertical height axis is the navigation. No sibling app in the catalogue shares its silhouette.
Every endpoint curl-checked before it entered the catalogue; 35 assertions run the shipped geometry and the regulation against live services.
Runs on your infrastructure, keyless, EPSG:4326 — and re-pointing it to another state or country is configuration, not development.
Three traps in the public data cost real time and are now documented in the build: the runway table keys on a GUID, obstacle type codes are space-padded, and runway geometry is never a centreline.
Running today on real FAA, USGS and Caltrans data. Point it at your airports, your compatibility zones, your counter — and give everyone who asks "how tall can I build here?" a defensible answer in one screen.