A camera-based calibration for automotive augmented reality Head-Up-Displays

Using Head-up-Displays (HUD) for Augmented Reality requires to have an accurate internal model of the image generation process, so that 3D content can be visualized perspectively correct from the viewpoint of the user. We present a generic and cost-effective camera-based calibration for an automotive HUD which uses the windshield as a combiner. Our proposed calibration model encompasses the view-independent spatial geometry, i.e. the exact location, orientation and scaling of the virtual plane, and a view-dependent image warping transformation for correcting the distortions caused by the optics and the irregularly curved windshield. View-dependency is achieved by extending the classical polynomial distortion model for cameras and projectors to a generic five-variate mapping with the head position of the viewer as additional input. The calibration involves the capturing of an image sequence from varying viewpoints, while displaying a known target pattern on the HUD. The accurate registration of the camera path is retrieved with state-of-the-art vision-based tracking. As all necessary data is acquired directly from the images, no external tracking equipment needs to be installed. After calibration, the HUD can be used together with a head-tracker to form a head-coupled display which ensures a perspectively correct rendering of any 3D object in vehicle coordinates from a large range of possible viewpoints. We evaluate the accuracy of our model quantitatively and qualitatively

Phase diagram of the system CaSO 4 -K 2 SO 4 -KNO 3 -Ca(NO 3 ) 2 -H 2 O

Abstract: Potassium nitrate as a fertilizer suitable for greenhouse and hydroponic applications can be prepared by the reaction of potassium sulphate with calcium nitrate. However, it may happen that simultaneously with the precipitation of gypsum (CaSO 4 ·2H 2 O) also two other binary salts, viz. syngenite (K 2 SO 4 ·CaSO 4 ·H 2 O) and görgeyite (K 2 SO 4 ·5CaSO 4 ·H 2 O) can crystallize. This would lower the yield of KNO 3 . For minimization of potassium loss we have to determine the conditions under which syngenite and görgeyite crystallize. As a useful tool for the quantitative determination of specifi c hydrates, simultaneous DTA/TG technique appeared. Each hydrate decomposes at a certain temperature. The loss of water at dehydration can be used for a quantitative determination of the amount of the hydrate in the precipitating solid phase. Based on the experimental data several conclusions can be drawn: (i) excess of calcium cations lowers the concentration of sulphate ions in the liquid phase together with lowering of contents of syngenite and görgeyite in the solid phase; (ii) higher content of water results in a higher solubility of sulphate ions; (iii) joint crystallization of syngenite and gypsum occurs in the composition area interesting from the point of KNO 3 production; (iv) area of the primary crystallization of görgeyite does not exist in the phase diagram at 80 °C. However, görgeyite crystallizes at the molar ratio Ca(NO 3 ) 2 :K 2 SO 4 = 1:1 by ternary crystallization; (v) area of crystallization of pure gypsum is shifted to lower ratio Ca(NO 3 ) 2 :K 2 SO 4 by the addition of water to the system