The task of automatic calibration of the projector and the sensor depth

Augmented reality system, built with use of projectors and sensors depth using infrared light, are widely used in various fields - from the defense to the gaming industry. In such systems, the actual problem is the calibration of the projector display information and sensor depth, reading the data in the space. One of options using technology of augmented reality is the "Virtual sandbox" representing a combination of a normal sandbox, the three-dimensional sensor Microsoft Kinect, the software of simulation and visualization and also from the normal projector (sometimes several projectors) providing visualization of submission of the image. The landscapes created from sand are selected in real time with the flowers corresponding to elevation height, topographical planimetric lines and the virtual water. In systems of augmented reality, where a role of interactive devices is played by the sensor controller and a projector for visual modification of a scene, there is a need of the solution of the task of determination of geometry of a surface of real space and comparison of this surface to the projected image. Process of calibration of both devices is usually carried out in a manual mode independently by the user of system that doesn't allow to receive rather precisely necessary conversion and as a result doesn't allow to achieve the desirable level of display of the virtual view. In certain cases process of calibration becomes technically difficult or generally impossible. The task of calibration can be solved by formalization of algorithm of automatic calibration of system which program implementation allows to receive necessary transformation of coordinates by system in an automatic mode. In development process of difficult program systems of simulation and visualization, which cornerstone graphic job processing is, there is a need of comparison of coordinate of a cloud of the points accepted from a sensor of depth and coordinate of space, projected by a projector. Such actions will allow to add the real image data of the virtual space. This article discusses options for using interactive devices. We have proposed a stepwise algorithm for determining the mutual position of the sensor space and depth of the projector image: 1. Projection, search and determination of depth; 2. Conversion of local coordinates of the sensor to global coordinates; 3. Determination of coordinates of layout of a projector; 4. Projection direction finding; 5. Receiving transformation from global space in local space of a projector; 6. Receiving the general conversion of local coordinates of the sensor to local coordinates of a projector. The necessary steps pretreatment process are defined that allow to carry out the calibration of the projector automatically. The mechanism of projection, search and determination of the depth are presented. The principle of conversion of the local coordinates of the sensor in global coordinates is described. A method for determining the coordinates of the location of the projector and the determination of the direction of projection is proposed. The process of transformation of the global space in the local space of the projector is described. A version of obtaining a general transformation of the local coordinates of the sensor in the local coordinates of the projector is presented. The mathematical component optimally integrable in computer graphics processing systems through the use of common principles, requires minimal changes in the system processing and analysis of complex structured images. The proposed algorithm can be used in augmented reality systems with both single and multiple projectors. In the latter case calibration is carried out in pairs, with adding of a stage of receiving a relative positioning of coordinate axes of different couples. Also considered algorithm can be taken as a basis for use in systems of augmented reality when manual calibration of devices is represented difficult or impossible.

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