The paper describes a technique that allows measuring and annotating real objects in an Augmented Reality (AR) environment. The technique is based on the marker tracking, and aims at enabling the user to define the three-dimensional position of points, within the AR scene, by selecting them directly on the video stream. The technique consists in projecting the points, which are directly selected on the monitor, on a virtual plane defined according to the bi-dimensional marker, which is used for the tracking. This plane can be seen as a virtual depth cue that helps the user to place these points in the desired position. The user can also move this virtual plane to place points within the whole 3D scene. By using this technique, the user can place virtual points around a real object with the aim of taking some measurements of the object, by calculating the minimum distance between the points, or in order to put some annotations on the object. Up to date, these kinds of activities can be carried out by using more complex systems or it is needed to know the shape of the real object a priori. The paper describes the functioning principles of the proposed technique and discusses the results of a testing session carried out with users to evaluate the overall precision and accuracy.
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