EarthSight needs JavaScript to run the interactive globe and visibility solver. The documentation pages remain available from How it works.

WGS‑84 geometric line of sight

How tall must it be to become visible?

Choose two points. EarthSight solves the minimum tower height on the WGS‑84 ellipsoid.

1 Observer

Latitude Longitude

Ground height (m) Eye height (m)

2 Tower base

Latitude Longitude

Ground height (m)

Solved minimum

Vertical tower height

WAITING

Choose two points

Select an observer and tower base to solve the WGS‑84 geometric minimum.

Surface distance—

Initial bearing—

Solver details numeric & tangent diagnostics

Final bearing—

Finite-height limit—

Remaining to hard limit—

Tangent—

Solver confidence—

Numeric diagnostic—

Advanced toolsLive probe, fixed-height visibility and model notes +

3 Live globe probe

Move across Earth to calculate the WGS‑84 minimum at the cursor without changing the selected tower.

Live hover calculator

Off · enable it, then hover over the globe.

4 Check a chosen tower height

Tower height

Choose a tower base first.

Calculation model

The baseline result uses the WGS‑84 reference ellipsoid in Earth‑Centered Earth‑Fixed coordinates. The tower rises along the local geodetic normal. A straight finite sightline is tested against the ellipsoid interior. Surface distance and bearings are solved geodesically with GeographicLib. Manual ground/eye heights are WGS‑84 ellipsoidal heights, not mean-sea-level/orthometric heights. Ground relief, geoid conversion and atmospheric refraction are not modeled.

1 Visibility boundary

Set a tower height and EarthSight solves the WGS‑84 horizon independently for every azimuth. The result is not forced to be a circle.

Tower height (km) Angular step

1 km10 km100 km1,000 km10,000 km100,000 km

Boundary statistics

Nothing drawn yet

Mean radius—

Minimum—

Maximum—

WGS‑84 spread—

2 Boundary appearance

Fill opacity 10% Fill visible region Show azimuth spokes

True country size · WGS‑84

Compare countries without the map illusion

Compare geodesic surface area, overlay two country footprints, and drag country B across Earth to see how 2D projections change apparent size.

1 Countries

Country A Country B

Country data loads only when this tool is opened.

2 Move & inspect

Overlay opacity 34%

Drag mode is explicit: left-drag moves country B, right-drag rotates Earth, and the wheel zooms. You can also use WASD or the arrow keys to rotate the globe (hold Shift for larger steps). The original country geometry is never rewritten. Touch: toggle Drag mode off whenever you need normal one-finger globe navigation.

Geodesic area on WGS‑84

Country A—

Country B—

Area ratio—

B anchor—

3 Projection view

Projection

Globe mode shows both footprints directly on the WGS‑84 ellipsoid.

Country-boundary data & interpretation

Boundaries come from the public-domain Natural Earth 1:110m admin-0 dataset and are intended for small-scale visualization. Natural Earth follows practical cartographic conventions for disputed areas; the display is not a statement on sovereignty. Surface-area values are computed in the browser from the displayed polygons on the WGS‑84 geodesic model.

1 Performance

Rendering quality

AUTO · BALANCEDmove globe to measure

Rendering quality changes only the 3D display, never WGS‑84 calculation precision.

Advanced rendering

Render only when the scene changes

Ultra lowers render resolution and disables FXAA for maximum responsiveness.

2 Globe & map filters

Imagery

Bare globe removes map tiles, place names and optional visual effects in one click. Press it again to restore normal visuals.

More visual filters

Atmospheric rendering Sun lighting EarthSight geometry labels Country borders in Minimal mode

OpenStreetMap place names are baked into raster tiles. Use Minimal/Bare globe to remove them.

Auto-frame after drawing geometry

Geometry is drawn at true scale. For extreme tower heights Earth can become tiny; use Globe or G to jump back instantly.

3 Units & persistence

Display units Remember last coordinates locally

Off by default. Share links contain the exact coordinates shown and require confirmation. v1.16.0 creates new share coordinates only in the URL fragment. Old ?lat= query URLs are ignored by EarthSight, but the browser/server may already have received that legacy query before the app can ignore it.

Privacy & external services

Place search sends the text you type to OpenStreetMap Nominatim. Map imagery is requested from the selected tile provider. Country Compare lazily downloads the public Natural Earth country-boundary dataset from a pinned CDN URL with a GitHub fallback. Browser geolocation is only requested after you press My position; EarthSight does not persist coordinates unless you enable local remembering. Public-beta privacy, advertising and external-service details are available on the Privacy page.

4 Export

Keyboard shortcuts

O pick observer T pick tower F fit geometry G globe view V top-down view B undo camera Esc cancel active mode WASD rotate globe in Country drag

WGS‑84 engine ready

Cursor—

Camera—

Learn Math Accuracy FAQ Privacy

EarthSight 1.16.0 · Public Beta

Click the globe

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