Horizon Line Planning Guide
Why the Horizon Changes
Horizon planning is useful for sailors, walkers, photographers, surveyors, and students. The visible horizon is not fixed. It changes when the eye height changes. A taller observer sees farther because the line of sight touches Earth at a later point.
How Refraction Affects Results
This calculator treats Earth as a sphere. It can also use an effective radius when refraction is included. Standard refraction bends light slightly toward Earth. That bend lets you see a little farther than pure geometry predicts. You can change the factor when local air layers are unusual.
Main Measurements
The main result is horizon distance. It is the ground distance from the observer to the tangent point. The tool also reports dip angle. Dip angle tells how far below true level the sea or land horizon appears. This helps with photography, mapping, and camera framing.
Target Visibility
Advanced fields add target height and target distance. A target has its own horizon distance. When both horizon distances overlap, the target should be visible in simple clear-air geometry. When the target is beyond that limit, the hidden height estimate shows how much may fall below the curve.
Image Placement
The image line option is for visual work. Enter image height, vertical field of view, and camera pitch. The calculator estimates the pixel row where the horizon line should appear. A level camera places the horizon slightly below center because of dip. A downward tilted camera moves it upward.
Practical Limits
Results are estimates, not legal survey data. Real visibility depends on haze, waves, terrain, temperature gradients, lens distortion, and exact elevation. Use verified geodetic tools for navigation or engineering. Use this page for fast planning, learning, and layout checks.
Best Input Tips
For best results, measure observer height carefully. Use eye height, not total body height. Choose a realistic Earth radius. Keep units consistent by using the unit selectors. Compare several refraction values when conditions are changing.
Exporting Results
You can use the example table to understand common cases. A person near the beach sees only a short range. A cliff, tower, drone, or ship bridge extends the view greatly. Export the result after each calculation. The files are useful for notes, lesson pages, and repeated field checks. They also support simple client reports.