Camera placement principles
Basic principles
Camera field and angle of view
The camera field of view is usually characterized by the combination of distance and scene dimensions (image width and height)
Scene dimensions for a given distance are determined by the camera’s angle of view. The camera’s angle of view is determined by the focal length of the lens being used.
Focal length
The focal length of a lens is the distance between the optical center of the lens and the image sensor. The longer the focal length, the more it “magnifies” the subject.
The diagram below illustrates the reciprocal relations between the focal length, angle of view, and image magnification (aka zoom level).
Conclusions
- Short focal length provides a wider angle of view, generating a wide (zoomed-out) image
- The long focal length provides a narrower angle of view, generating a narrow (zoomed-in) image
Camera Mounting Options and Impact on Field of View
Angled mounting and tilt angle
The tilt angle is the angle between the camera’s lens position and the ground, as illustrated in the above diagram. The relevant tilt angle range is between 0 to 90 degrees.
Angled camera mounting refers to positioning a camera with a tilt angle of less than 85-90 degrees. In practice, angled cameras are typically positioned with a tilt angle varying between 10 to 40 degrees.
Dead-zone
The area between the position of the camera and the closest viewing point is referred to as the dead-zone.
The camera is completely blind across the dead-zone. In other words, this area is excluded from the camera’s field of view.
Detachable height and area
This is the maximum height that can be detected at a particular distance from the camera. The detectable height decreases when the distance from the camera is increased. Therefore, the maximum viewing distance is determined according to the point where the detectable height is equal to the expected target height, and the detectable area, aka effective field of view, is the area between the closest viewing point (end of dead-zone) and the maximum viewing distance.
Correlation between tilt angle, dead zone, and viewing distance for a given lens and camera height:
Tilt Angle
Tilt angle is the angle between the camera’s lens position and the ground, as illustrated in the above diagram. The relevant tilt angle range is between 0 to 90 degrees.
Angled camera mounting refers to positioning a camera with a tilt angle less than 85-90 degrees. In practice, angled cameras are typically positioned with a tilt angle varying between 10 to 40 degrees.
Dead-Zone
The area between the position of the camera and the closest viewing point is referred as the dead-zone.
The camera is completely blind across the dead-zone. In other words, this area is excluded from the camera’s field of view.
Viewing Distance
Conclusion
- Decreasing the tilt angle increases the viewing distance as well as the dead-zone
- Short range detection is typically achieved with an increased tilt angle towards overhead mounting which eliminates the dead-zone
Camera placement design tool
To perform criteria verification, identify the scenarios relevant to your case and measure the size of target objects using one of the following methods:
- Use a camera design tool to determine the pixel-per-meter/feet ratio for a given camera at the minimum and maximum distances, and calculate the size criteria according to the relevant scenario.
- We always recommend the quick and easy Irisity Planning Application at https://plan.irisity.com
- For very complex installations, do use a more complex tool such as the IP Video System Design Tool which can be found at www.jvsg.com. This type of tool allows users to input the various camera parameters (resolution, focal length, installation height, etc.) and place the cameras on top of a map or satellite image to view the resulting coverage areas for each camera.
- If cameras are already placed, you can retrieve relevant footage and screenshots, with relevant target objects in the field of view, and calculate their relative size using an on-screen pixel measurement tool. A recommended tool is "Measure" which can be found at http://www.cthing.com/.