An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Vision Triangulation <s> High power white LEDs are expected to replace the existing lighting technologies in near future which are also suggested for visible light communication (VLC). We proposed an algorithm for high precision indoor positioning using lighting LEDs, VLC and image sensors. In the proposed algorithm, four LEDs transmitted their three-dimensional coordinate information which were received and demodulated by two image sensors near the unknown position. The unknown position was then calculated from the geometrical relations of the LED images created on the image sensors. We described the algorithm in details. Simulation of the proposed algorithm was done and presented in this paper. This technique did not require any angular measurement which was needed in contemporary positioning algorithms using LED and image sensor. Simulation results showed that the proposed system could estimate the unknown position within the accuracy of few centimeters. Positioning accuracy could be increased by using high resolution image sensors or by increasing the separation between the image sensors. DOI: http://dx.doi.org/10.11591/ijece.v1i2.165 <s> BIB001 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Vision Triangulation <s> High power white LEDs are expected to replace the existing lighting technologies in near future which are also suggested for visible light communication (VLC). We propose an algorithm for high precision indoor positioning using lighting LEDs, VLC and image sensors. In the proposed algorithm, at least three LEDs transmit their three dimensional coordinate information which are received and demodulated by two image sensors at the unknown position. The unknown position is then calculated from the geometrical relations of the LED images created on the image sensor. This technique does not require any angular measurement. Results from the numerical simulations are explained to understand the effect of different system parameters on positioning accuracy. Based on numerical analyses, we show that the system is able to estimate the unknown position within the accuracy of about 10 centimeters. Positioning accuracy can be increased by using high resolution image sensors. <s> BIB002 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Vision Triangulation <s> We show the successful implementation of indoor positioning by using four single LEDs and dual PC cameras. Each LED having its position information is identified by the different color. The required unknown position is then calculated using the position information of the LEDs and the geometric relationship of the images on the two image sensors. And a vector estimation algorithm is also used to solve a set of four quadratic equations. To remove a fluctuating due to the quantization error of the pixel, we compute the center of an image in terms of decimal point pixel and it brings the accuracy improvement. <s> BIB003 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Vision Triangulation <s> SUMMARY This study introduces an image sensor based visible light communication (VLC) and its application to pose, position, and range estimations. There are two types of visible-light receiver: a photodiode and an image sensor. A photodiode is usually used as a reception device of VLC, and an image sensor consisting of a large number of pixels can also be used as a VLC reception device. A photodiode detects the signal intensity of incoming light, while an image sensor not only detects the incoming signal intensity but also an accurate angle of arrival of light emitted from a visible light transmitter such as a white LED light. After angles of arrival of light are detected by an image sensor, positioning and data reception can be performed. The ability of an image sensor to detect an accurate angle of arrival will provide attractive applications of VLC such as pose, position calculation, and range estimation. Furthermore, because the image sensor has the ability to spatially separate sources, outdoor positioning even with strong <s> BIB004
Vision triangulation is a method for 3D position measurement of an object in the real world with multiple known cameras as illustrated in Figure 13 . Suppose that P 1 and P 2 are the projections of a 3D point P on two cameras, the relation between the world coordinate of P and the two image coordinates of P 1 and P 2 is mathematically described as BIB004 : where M i is a 3 × 4 perspective projection matrix of i th camera defined as BIB004 : Figure 13 . Two-view geometry. Usually in a system the calibration matrix C i of all cameras is the same. The relative position and orientation of one camera to other is assumed to be known and thus the rotation matrix R i and the translation vector t can be represented using the parameters of one camera. When Equation (25) is expressed in the form of collinearity conditions as in Equation (21), six parameters need to be found given that the focal length f which defines the camera calibration matrix is known. Least squares methods can be used to solve these equations to determine the camera position. Other methods which do not use collinearity conditions are presented in BIB001 BIB002 BIB003 . In BIB001 BIB002 , two cameras installed in the mobile device are used to estimate the distance from the mobile device to four LED base stations. With four estimated distances, the position of the mobile device is determined using the trilateration method. Simulation results show that a positioning accuracy of 1.5 m is achieved by this system. An implementation of the system proposed in BIB001 BIB002 was conducted in BIB003 . Two webcams attached to a PC were used to take the images of four LEDs installed on the ceiling. The accuracy was improved by using higher resolution sensor and by computing the center of an image in terms of a decimal point pixel to reduce the quantization error. The experiment results show that an accuracy of 0.85 m, a 61% improvement over the previous system, was achieved.