All these camera systems are used in surveying using photogrammetry as the methodology.
Close-range photogrammetry is the ingenious technique of retrieving spatial data such as the size and position of objects from two-dimensional images. Using specialised software, the images are processed into a 3D model. This model can extract information such as dimensions, angles and surfaces.
The table points to some pros and cons of using single, stereo and multi-camera systems.
| Topic | Single camera | Stereo camera | Multi camera |
|---|---|---|---|
| Texture on surveyed objects can be used to extract information | Extensive marking | Reduced or no marking | Reduced or no marking |
| Surface model | Possible but not easy | Easy | Easy |
| The surveyed object can move during image acquisition | No | Yes | Yes |
| The camera system can move during the image acquisition | Yes | Yes | Yes |
| A 3D model can be produced from images acquired from one position | No | Yes | Yes |
| Accuracy | High. Based on multiple intersections from different camera positions | Medium. Based on intersections from two cameras. One pair of coordinate per point. | High to medium. Based on intersections from three or more cameras. Four cameras will enable six pairs of coordinates for each surveyed point. |
| High dynamic range High dynamic range (HDR) is the technique of combining two or more images to balance highlights and shadows in a scene | Difficult or impossible | Limited | Easy |
The more intersections to the surveyed points, the better the chances for an accurate and precise position of the point relative to the other points within one single recording.
Recording using two or more cameras built into one system will give these possible intersections for each point surveyed on the object.
| Number of cameras | Number of intersections |
|---|---|
| Two | 1 |
| Three | 3 |
| Four | 6 |
| Five | 10 |
