Collaborative sighting

Collaborative sighting is performed using plural optical sighting apparatus that each comprises a camera unit and a display device. Geometric calibration of the camera units with respect to the imaged scene is performed by detecting features within captured images (Figure 6, S61), generating descriptors from respective patches of the image at the features (Figure 6, S62), detecting corresponding descriptors from different images S4, and deriving the geometric calibration from the positions in the respective images of the corresponding descriptors S5. A target location in the image captured by a first optical sighting apparatus is designated and a corresponding location relative to the image captured by the second optical sighting apparatus is identified from the geometric calibration S6. The display device of the second optical sighting apparatus indicates where the corresponding location lies relative to the displayed image S7. The descriptors may be generated using techniques such as ...