line of sight calculator

What Is Line of Sight?

Line of sight (LOS) is the direct, unobstructed path between two points. In practical terms, LOS determines whether one location can directly “see” another location. This is important for radio communication, visual observation, microwave links, drone operations, marine navigation, and even simple tower placement.

On a perfectly flat world, LOS would mostly be limited by obstacles like buildings and hills. On Earth, curvature adds another limit: even with no terrain in the way, objects eventually disappear below the horizon as distance increases.

How This Calculator Works

This tool estimates horizon-limited line-of-sight distance using a spherical Earth model. It computes the horizon distance from each height, then adds those distances together:

• Horizon distance from observer height
• Horizon distance from target height
• Total LOS distance = observer horizon + target horizon

The calculator uses an effective Earth radius factor k, which can model atmospheric refraction. A higher k value slightly extends LOS distance.

Formula Used

For each height h, with effective Earth radius R_eff = k × R:

d = R_eff × arccos(R_eff / (R_eff + h))

Then:

d_LOS,max = d_observer + d_target

This provides a clean and reliable estimate for many planning scenarios.

When to Use This LOS Calculator

• Radio and wireless links: Estimate whether two antennas can see each other over distance.
• Drone missions: Understand long-range visual or signal constraints.
• Marine navigation: Approximate visibility range of coastal structures or vessels.
• Field surveying: Plan observation points and instrument setup heights.
• Emergency communications: Evaluate temporary repeater or tower deployment options.

Example

Suppose an observer is at 2 m height and a target tower is 50 m high (k = 1.00). The tool computes each horizon distance and combines them. The result is often much larger than people expect, because even modest height increases can significantly improve LOS range.

If you enter a real-world separation in the optional field, the calculator also reports whether that separation is within the estimated LOS limit.

Important Limitations

This calculator is intentionally simple and fast. It does not account for:

• Terrain elevation changes (hills, valleys, ridgelines)
• Buildings, vegetation, or man-made obstructions
• Fresnel zone clearance (critical for RF links)
• Weather effects and dynamic atmospheric layers
• Earth ellipsoid/geodesic corrections for precision surveying

For engineering-grade link design, combine this estimate with topographic profiles, clutter data, and full propagation modeling.

Quick Tips for Better LOS Planning

1) Increase height before increasing power

Raising antenna or sensor height often improves connection reliability more than boosting transmit power alone.

2) Keep units consistent

Use either meters or feet throughout your inputs. This calculator converts internally, but consistent thinking helps avoid planning mistakes.

3) Treat results as a first-pass screen

Use the output to shortlist feasible sites, then verify with maps, terrain profiles, and on-site testing.

Bottom Line

A line of sight calculator is a practical first tool for distance feasibility. With only a few inputs—observer height, target height, and optional separation—you can quickly estimate whether curvature alone allows visibility. It’s fast, useful, and an excellent first step before deeper engineering analysis.