How it works
This rectilinear pinhole model uses sensor width, height and actual focal length in millimeters. Distance is measured along the optical axis from the idealized camera viewpoint to a flat plane perpendicular to that axis. Coverage uses the same length unit as distance. Real lens geometry, distortion, focus breathing and close-focus magnification can change the result. The model does not calculate the footprint on tilted ground or prove that a lens covers a sensor.
The formulaHorizontal angle = 2 × atan(sensor width ÷ (2 × focal length))
Vertical angle = 2 × atan(sensor height ÷ (2 × focal length))
Coverage width = distance × sensor width ÷ focal length
Coverage height = distance × sensor height ÷ focal length
Pixel density = output pixels ÷ coverage length
Angles displayed in degrees
Put it into practice
EXAMPLEA 36 × 24 mm active sensor with a 50 mm lens at 10 m gives about 39.598° horizontal and 26.991° vertical view. Its perpendicular-plane coverage is 7.2 × 4.8 m. These are illustrative dimensions, not a camera preset.
EXAMPLEWith the same sensor and distance, changing a 4 mm lens to an 8 mm lens halves the predicted coverage width and height. A 1,920-pixel image spanning 8 m averages 240 horizontal pixels per meter; this alone does not establish image detail or identification performance.
Good to know
Where do I find active sensor dimensions?
Use the camera or sensor datasheet for the active imaging width and height in the recording mode you use. A label such as 1/2.8 inch is an optical-format name, not a literal width, height or diagonal. Do not convert that fraction to millimeters. If documented pixel pitch and active pixel counts are available, dimension in mm = pixel count × pitch in micrometers ÷ 1,000.
Which focal length should I enter?
Enter the actual focal length in millimeters for the lens setting in use, not a 35 mm-equivalent focal length. This approximation assumes a rectilinear lens. Fisheye, panoramic and telecentric lenses require different models.
What about digital crop or stabilization?
Enter the physical sensor area actually used by that mode. Digital zoom, stabilization, aspect-ratio crop, dewarping and output resizing can change coverage or sampling. Use the output resolution corresponding to that same area; do not assume the full sensor dimensions apply to a cropped stream.
Does the diagram show ground coverage?
No. It shows a target plane perpendicular to the viewing axis, with the camera aimed at its center. Tilting a camera toward the ground changes the footprint and sampling across it; mounting height and tilt are not modeled.
Can pixel density guarantee recognition or identification?
No. It is average geometric sampling on the stated plane, not an identification rating. Lens sharpness, focus, motion, lighting, noise, compression and subject angle all affect usable detail. Verify a real image at the intended installation.