This paper presents an application of some recent results in computer vision, in particular the use of geometric properties. The problem we examine here is the accurate positioning of an object with respect to another, say a tool. Such applications could be used in complex and hazardous environments like nuclear plants. Because high accuracy in positioning is our goal here, we suppose that the objects have planar faces on which targets can be put. Without loss of generality, we have used only two objects in our experiments. Throughout this paper, we have called them the reference object and the unknown object respectively. The positions of the targets of the reference object with their associated projective invariants are computed in an off-line stage. Hence, given at least two images of the two objects, we can automatically identify the reference object points in the images and reconstruct the points of the unknown object relative to the reference object. The experiments show that a precision of 0.1 mm in relative positioning can be reached for an object observed at a distance of 2 m.