Line-of-Sight Clearance Calculator

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Run a calculation to enable CSV and PDF export.

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Calculator Inputs

Enter heights, elevations, and distances. The calculator checks clearance at the obstacle location and compares it to the required safety margin.

Units

All inputs and outputs follow this unit.

Observer height (m)

Height of the source point above its ground.

Observer ground elevation (m)

Absolute or relative elevation; stay consistent.

Target height (m)

Height of the destination point above its ground.

Target ground elevation (m)

Use the same reference as the observer.

Total distance (m)

Horizontal separation between observer and target.

Obstacle distance from observer (m)

Where the obstruction sits along the path.

Obstacle height (m)

Height of the obstruction above its ground.

Obstacle ground elevation (m)

Use the same elevation reference as endpoints.

Safety clearance margin (m)

Extra clearance required above the obstacle.

Include curvature / refraction

Useful for long distances.

Refraction k-factor

Common default is 1.333 for standard conditions.

Reset

Example Data Table

These sample values illustrate typical use cases for planning sightlines for cameras, work zones, and temporary structures.

Units	Observer height	Observer elev.	Target height	Target elev.	Total distance	Obstacle dist.	Obstacle height	Obstacle elev.	Safety margin	Curvature
m	2.0	100.0	2.0	100.5	250	120	4.0	100.2	0.5	No
m	1.7	0	1.7	0	2000	1000	2.5	0	0.6	Yes (k=1.33)

Note: For long distances, enabling curvature can significantly change results.

Formula Used

Endpoint top elevations: H₁ = E₁ + h₁, and H₂ = E₂ + h₂.
Line height at obstacle distance x: H_line(x) = H₁ + (H₂ − H₁) · (x / D).
Obstacle top elevation: H_obs = E_obs + h_obs.
Curvature/refraction bulge (optional): b(x) = x · (D − x) / (2 · R_eff), where R_eff = k · R.
Effective obstacle top: H_eff = H_obs + b(x).
Available clearance: C_avail = H_line(x) − H_eff.
Pass/Fail rule: PASS if C_avail ≥ C_safe.

All calculations are performed internally in meters, then converted to the selected unit.

How to Use This Calculator

Select your unit system and keep all inputs consistent.
Enter observer and target heights above ground (e.g., camera or platform height).
Enter ground elevations for observer, target, and obstacle using the same reference.
Enter total distance and the obstacle distance measured from the observer.
Enter the obstacle height and required safety clearance margin.
Enable curvature/refraction for long baselines and adjust the k-factor if needed.
Click Calculate Clearance to see results above this form.
Use the CSV/PDF buttons to export the latest computed report.

Line-of-Sight Clearance Planning in Construction Environments

1) Common construction use cases

Line-of-sight checks are frequently needed for CCTV mounting, hoist-way monitoring, plant operator visibility, temporary traffic control, and alignment of radios or laser references. A clear path reduces blind zones and supports safer sequencing. This calculator is also useful when placing temporary screens, safety netting, or storage stacks that may block a critical view corridor.

2) Inputs that drive accuracy

Accuracy depends on consistent references. Heights represent the mounting elevation above local ground, while ground elevations represent survey levels or a chosen site datum. A typical site camera may sit 2–6 m above grade, while temporary platforms and scaffolds can add several meters. Modeling the obstacle’s own ground elevation avoids underestimating clearance on sloped terrain.

3) Clearance margin as a project control

The safety margin is not “extra math”; it is a practical control for tolerance and change. Stockpiles can grow, scaffolds can be reconfigured, and equipment can sway or reposition. Many teams use margins between 0.3 and 1.0 m for general planning, then increase the margin for higher-risk zones or where future stacking is likely.

4) Curvature and refraction for long baselines

Over kilometer-scale distances, earth curvature can reduce apparent clearance. For example, with a 2,000 m baseline and an obstacle at midspan, a curvature bulge on the order of 0.2 m may appear, depending on the refraction k-factor. Enabling curvature provides a conservative check when planning long corridors, perimeter monitoring, or cross-site visibility requirements.

5) Turning results into actions

When the result fails, the “additional height needed” outputs provide direct options: raise the observer point (higher pole, platform, or bracket), raise the target point, or relocate to shorten the baseline. If raising is not feasible, reduce obstacle height (regrade, lower storage limits) or shift the alignment. Exporting CSV/PDF helps document assumptions for coordination meetings and method statements.

FAQs

1) What does PASS mean?

PASS means available clearance at the obstacle point is at least the safety margin you entered, after applying elevations, heights, and optional curvature/refraction effects.

2) Do I need survey elevations to use it?

No. You can use a relative datum by setting one location to zero and entering other elevations relative to it. Just keep the same reference for observer, target, and obstacle.

3) How should I choose the safety margin?

Select a margin that covers tolerances and likely site changes. Use larger margins where stockpiles grow, equipment moves, or risk is higher. Document the chosen value in your planning notes.

4) What is the k-factor used for?

The k-factor models atmospheric refraction by adjusting the effective earth radius. Higher k reduces the curvature bulge. A common planning value is about 1.33, but conditions vary.

5) Why is obstacle “effective top” higher with curvature?

Curvature makes the earth’s surface bulge upward relative to the straight chord between endpoints, which reduces clearance. The calculator adds this bulge to the obstacle elevation when enabled.

6) Can I model multiple obstacles?

This version checks one obstacle at a chosen distance. For multiple obstructions, run the calculator for each obstruction location and use the worst-case (smallest) clearance result.

7) Is this suitable for crane visibility checks?

Yes for planning visibility lines. Enter the operator or camera height, the target height, and model the obstruction. For lifting operations, follow project-specific safety procedures and approvals.