How CCTV Design Tool calculates field of view and pixel density
The formulas, units, assumptions and limits behind the numbers. This page covers the optics used by the public FOV calculator and by the designer.
Scope
This page describes how the field of view, scene width, pixel density and level reached are calculated. It does not describe wall detection, simulation or reporting.
The FOV calculator and the designer call the same optics functions. Automated tests compare the calculator's results with those functions for reference cameras, so the two cannot drift apart without a test failing.
Units and conventions
| Quantity | Unit | Convention |
|---|---|---|
| Sensor size, focal length | millimetres | Sensor width and height are the active dimensions. Format names such as 1/2.8 inch are nominal. |
| Resolution | pixels | Horizontal and vertical pixels of the recorded image. |
| Distances, heights | metres | Target distance is measured along the camera's viewing direction. |
| Angles | degrees | Tilt is measured below horizontal: 0 is level, positive points down. |
| Pixel density | pixels per metre (px/m) | Horizontal pixels divided by the scene width at the target. |
Field of view
The active sensor height is the sensor height, cropped so that it matches the aspect ratio of the recorded resolution. A 4:3 sensor recording 16:9 uses its full width and part of its height. The horizontal field of view always uses the full sensor width. The number of pixels does not change either angle.
The model represents rectilinear lenses between 1 and 179 degrees. Outside that range the calculator asks for a correction instead of returning a clamped value. Above 120 degrees horizontal it shows a warning, because real wide-angle lenses distort and the pinhole model overstates coverage near the image edges.
Scene size and pixel density
These describe a flat target facing the camera at the target distance, on the viewing direction. They are the same at any tilt. The floor a tilted camera sees is a different shape, which the side view addresses separately.
Level reached
The level is the highest one in the table whose pixel-density requirement is met at the target distance. The distance up to which each level is reached follows from the same formula solved for distance.
| Level | Requirement | Status of the value |
|---|---|---|
| Monitor | 12.5 px/m | Extended level used by the designer. Not one of the four DORI levels. |
| Detect | 25 px/m | DORI level, as published in EN 62676-4 guidance. |
| Observe | 62.5 px/m | DORI level, as published in EN 62676-4 guidance. |
| Recognize | 125 px/m | DORI level, as published in EN 62676-4 guidance. |
| Identify | 250 px/m | DORI level, as published in EN 62676-4 guidance. |
| Inspect | 1000 px/m | Extended level used by the designer. Not one of the four DORI levels. |
The values in this table are read directly from the designer's code, so this page shows what the software uses. The four DORI values are those published in EN 62676-4 guidance; the standard's own text is not reproduced here. A level reached is a planning result, not a statement that the software or a camera is compliant with, certified by, or approved by any standard or authority.
Camera height and tilt
With a mounting height and a downward tilt, the upper and lower image edges leave the camera at the tilt angle minus and plus half the vertical field of view. Where each edge meets a flat floor gives the nearest and farthest floor the camera sees. If the upper edge points at or above the horizon, there is no far limit. If the lower edge points above the floor, no floor is visible.
What the calculation does not include
- Lens distortion, vignetting and lens breathing.
- Digital zoom, electronic stabilisation and other crops applied by the camera.
- Off-axis loss of pixel density. The calculator reports the density on the viewing direction.
- Walls, obstacles and glass. The designer models walls and openings; the calculator does not. See the blind-spot guide.
- Lighting, motion blur, compression and scene content, all of which affect whether a person can be recognised.
Limits on inputs
Sensor sizes 1 to 100 mm, focal length 0.5 to 2000 mm, resolution 160 to 16384 pixels per side, target distance 0.1 to 5000 m, camera height 0.1 to 200 m, tilt 0 to 89 degrees. Anything else is rejected with a message rather than silently replaced by a default.
Standards
- EN 62676-4:2015. The source of the DORI levels as published in manufacturer and industry guidance.
- IEC 62676-4:2025 (Edition 2.0, published 2025-10-09). IEC Webstore listing. The 2025 edition exists and revises the standard. The software's classification is based on the DORI levels above and does not implement the 2025 edition. Support will only be described here once it has been checked against the standard itself.
Versions
- Public FOV calculator: version 1.0.
- Designer plan-coverage model: rectilinear-plan-v4. The FOV calculator uses the optics functions that model is built on.
- Page last reviewed: 2026-09-21. Prepared by the CCTV Design Tool team; it has not been reviewed by an independent third party.
Read the field of view guide for a worked example, or the DORI and pixel-density guide for the levels.