Indoor triangulation system using vision sensors

Abstract: This thesis aims to investigate a triangulation system for indoor positioning in two dimensions (2D). The system was implemented using three Pixy2 vision sensors placed on a straight baseline. A Pixy2 consists of a camera lens and an image sensor (Aptina MT9M114) as well as a microcontroller (NXP LPC4330), and other components. It can track one or multiple colours, or a combination of colours.  To position an object using triangulation, one needs to determine the angles (α) to the object from a pair of known observing points (i.e., any pair of the three Pixy2s' placed in fixed positions on the baseline in this project). This is done from the Pixy2s' images. Using the Pinhole Camera Model, the tangent of the angle, tan(α), is found to have a linear relation with the displacement Δx in the image plane (in pixels), namely, tan(α) = k Δx, where k is a constant depending on the specific Pixy2. A wooden test board was made specially to determine k for all the Pixy2s. It had distance marks made in two dimensions and had a Pixy2 affixed at the origin. By placing a coloured object at three different sets of spatial sampling points (marks), the constant k for each Pixy2 was determined with the error variance of < 5%. Position estimations of the triangulation system were conducted using all three pairs formed from the three Pixy2s and placing the positioned object at different positions in the 2D plane on the board. A combination using estimation values from all three pairs to make a more accurate estimate was also evaluated. The estimation results show the positioning accuracy ranging from 0.03678 cm to 2.064 cm for the z-coordinate, and from 0.02133 cm to 0.9785 cm for the x-coordinate, which are very satisfactory results.      The vision sensors were quite sensitive to the light environment when finely tuned to track one object, which therefore has a significant effect on the performance of the vision sensor-based triangulation.      An extension of the system to use more than three Pixy2s has been looked into and shown to be feasible. A method for auto-calibrating the Pixy2s' positions on the baseline was suggested and implemented. After auto-calibration, the system still performed satisfactory position estimations.