Horizon Mapper
Use your phone to measure how much sky is actually clear at your planned site. Point the camera at an obstruction, set a point, done. The result goes straight into Stellarium, N.I.N.A. or the AstroCube scheduling planner.
Everything runs inside your phone browser. No images and no position data are sent to a server.
At a glance
Method: camera plus orientation sensors, crosshair on the top edge of the obstruction.
North reference: calibration on the sun or on a target with known coordinates.
Export: Stellarium ZIP, N.I.N.A. HRZ, JSON for the scheduling planner.
Requirements: opened over https, permission for camera and motion sensors.
Why the horizon decides the site
Check the site before you build
One tree in the south costs you half a season. Two metres further along it can be a different night. Measure both spots, compare the profiles and decide with numbers instead of a hunch.
Plan realistic observing windows
With a measured profile the scheduling planner tells you when an object really clears your obstructions, not when it merely rises above the mathematical horizon.
Automation without nasty surprises
N.I.N.A. and other controllers abort on a custom horizon. That keeps the mount from slewing into the neighbour's chimney at three in the morning.
How to measure it in about ten minutes
- 1
Stand at the planned telescope position
Measure where the optics will sit later, at objective height. One metre away the horizon already looks different.
- 2
Enter your location
On launch the app asks for your location automatically unless one is already stored. Under Setup you can refresh it or type it in at any time. Without a location the tool cannot compute the position of the sun and no north calibration is possible.
- 3
Calibrate north
Switch to Sun mode and put the crosshair on the sun using the screen only, never look at the sun through a camera or any optics. Without calibration the phone compass is often 5 to 10 degrees off.
- 4
Walk the obstructions
Aim at the top edge all around and set a point. At hard edges such as roof lines or wall corners, set one point just left and one just right of the edge. The strip at the bottom shows the emerging profile live.
- 5
Check and export
The Profile tab shows coverage and gaps. Gaps larger than 10 degrees are only bridged linearly, so add a point there. Then export.
What you take away
Stellarium (ZIP)
A ready landscape made of landscape.ini and horizon.txt. In Stellarium open Sky and viewing options, Landscape, plus symbol, pick the ZIP. Set the location in Stellarium yourself.
N.I.N.A. (HRZ)
Plain text file with azimuth and altitude per line for the custom horizon.
AstroCube scheduling planner (JSON)
Points, one degree profile, location and calibration data including raw values, so the measurement can be reloaded and extended later.
Accuracy and limits, stated plainly
- Without calibration on the sun or a target, azimuth depends on the phone compass. Errors of 5 to 10 degrees are normal, and considerably more near metal or magnets.
- Altitude comes from the accelerometers and is usually accurate to about one degree if the phone is held still. The scatter value shown per point tells you how shaky that reading was.
- Above roughly 80 degrees altitude the azimuth becomes mathematically unstable. Obstructions near the zenith cannot be captured cleanly this way.
- Gaps between points are bridged linearly. A single chimney between two widely spaced points simply disappears.
- Trees grow. A measurement is a snapshot, and with deciduous trees it also depends on the season.
Profile measured, site decided?
Send us the JSON along with your configuration request. We will check which tier and which wall height actually make sense at your site before we quote.