Space Location of Image in Urban Environments Based on C/S Structure

Aiming at the low positioning accuracy of image space location in urban environments, this paper proposes a new method of space location of image in urban environments based on C/S structure. First, a series of indoor images are taken in advance. We use the nearest neighbor distance ratio (NNDR) and normalized cross correlation (NCC) to get the SIFT coarse matches, then use RANSAC method to optimize it, and calculate the fundamental matrix and projection matrix. Building 3D point cloud model is established, and the object space feature library including image feature points, image point coordinates and object space point coordinates are got. Second, we regard the building images which are taken by user's mobile phone as the location images. Image feature points of location images are extracted and matched with the feature points of object space feature library, then the object space point coordinates are obtained. Finally, we use collinearity equation model to accurately calculate the exterior orientation elements, and display the user's space position on the phone, thus space positioning is realized. The experimental results show that the positioning method in this paper can reach the centimeter level positioning accuracy, and can meet the requirements of the user positioning accuracy.