Provided in the present invention is a projection unit, which is used for projecting an image to a target area containing a target object, said image having a certain gradual change rule and being unique in a certain spatial range. Also provided are a corresponding photographing apparatus, an imaging device, and a processor. The technical solution used by the present invention uses the projection unit to project, to the target area, an image which has a certain gradual change rule and which is unique in a certain spatial range, and a target object which projects such an image is photographed by means of a camera unit, thus avoiding repeated photographing and obtaining multiple images, and by means of combining relevant characteristics of the image, the accuracy of follow-up point cloud generation on a back-end processor is improved, while achieving good real-time performances.