CAMERA
Information 4-03-2021, 13:15 3 100 print
CAMERA
The system is organized in such a way that all images undergo photogrammetric calibration during processing. This makes it possible to use any modern photo or video camera for monitoring (from a phone to expensive mirror equipment) and get high-quality results.
Nevertheless, the camera is one of the three main elements of the technology, and the accuracy of the results directly depends on the quality of the images and the correct shooting.
CAMERA REQUIREMENTS
The most important requirement for the camera is the ability to provide sufficient detail of the image of the marker when shooting from the required distance. This depends primarily on the camera's focal length. The relationship between the shooting distance and the required focal length of the camera is presented in the table:
| Shooting distance (m) | 0.2 | 1 | 5 | 10 | 20 | 30 | 40 |
| Equivalent focal length of the camera (mm) | 14–55 | 40-200 | ≥200 | ≥400 | ≥800 | ≥1200 | ≥1600 |
The equivalent focal length of the camera is given in terms of the 36x24 mm frame format for matrices with a resolution of 15 - 20 megapixels.
MAIN FEATURES AND METHODS OF PHOTOGRAPHING
It is convenient to use cameras with lenses that have a variable focal length (Zoom lenses). So, using, for example, a TV-camera and a tripod, you can take pictures of markers located on the 10th floor of a building in the process of monitoring from the ground.
Another way to get a detailed image of a hard-to-reach marker is to use a quadrocopter.
For photographing at close range any camera is suitable.
2 methods of photographing can be used for monitoring – photogrammetric (shooting and processing single images, Fig.3) and stereophotogrammetric (shooting and processing two or more images, Fig. 4).
Fig. 3 Shooting and processing single images
Fig. 4 Shooting and processing two or more images
Stereophotogrammetric method is the main method of photographing. It provides a stable high accuracy of 3D measurements over the entire range of distances from 0.1 to 40 meters.
The photogrammetric method provides high accuracy of 3D measurements at photographing distances up to 0.3 m. At large shooting distances (up to 40 meters), single-image measurements can be used to monitor 2D movements in the wall plane. At the same time the pair of markers must be strictly on the same plane.