Fit the QR code from N.I.N.A. (Options → Plugins → Horizon Library) inside the box. Hold the phone about 20–30 cm from the screen.

Save horizon

Send to N.I.N.A. (recommended)

Laptop address

This opens the Horizon Library page on the laptop with this horizon attached. Name it there, or pick the saved horizon it replaces, then tap Save to N.I.N.A. The laptop needs the Horizon Library plugin and must be on the same Wi-Fi. Scanning the code fills in the address and the access code, which are kept on this phone only.

Or save a file

For loading by hand: in N.I.N.A., Options → General → Astrometry → Horizon.

Set the north reference

Put the crosshair on the reference, hold still, then tap. This lines up every direction in the app, including what you've already traced or scanned.

Landmark: measure its azimuth on a map, for example with the aerial helper under More. Sun: only through cloud or with the sun just behind an edge. Don't look at it directly. Polaris is within 1° of true north.

Horizons

Output

Safety margin (°) Altitude for directions with no data (°)

Camera

Field of view, long side (°)

The field of view affects the automatic mapping and the on-screen shading. Fix (hold) uses the crosshair, so it's exact either way. To check it, turn slowly: the red shading should stay stuck to the treetops instead of sliding.

Magnetic declination (°, west negative)

Night

Night mode

In night mode the sky isn't detected. Aim the crosshair at a treetop and tap Mark: each mark joins the last one with a straight line if it's within 30°. Hold to fix still works, and Undo takes back the last mark or fix. "When it's dark" switches on when the camera sees no sky.

Sky detection

Sky brightness at least Grey sky colourfulness at most

Aerial helper

Load a satellite screenshot with north at the top. Tap where you stand, then tap a landmark you can see from there. The landmark's azimuth becomes the default for the Landmark reference.

Reset

Your map and settings are stored only in this phone's browser. Nothing is uploaded, and no one else using this site can see them. The photos aren't kept, so use View horizon photo → Save photo before you close the app if you want the picture.

Horizon Tracer

Measures the horizon around your telescope for N.I.N.A. Stand where the mount goes.

How it works

Turn slowly in a full circle, holding the phone upright. Obstacles turn red as you go; tap Key for what each colour means.
Wherever the line is wrong, hold Fix and run the crosshair along the treetops.
Tap Save → Send to N.I.N.A. and name it on the laptop page, or pick the horizon it replaces.
To change a saved horizon later: Edit a horizon from N.I.N.A., tap Copy for editing on the laptop page, come back and tap Paste horizon.

North comes from the compass (±10°). For a more accurate file, use More → Set north precisely.