An Improved Method for Spatial Measurement in Surveillance Video

Abstract

Video detection technology plays an increasingly significant role in forensics and criminology. Measurement of real distance from single image frames is a key technology for many applications. There are several methods for the measurement, including proportion measurement, investigative experiment, perspective and projection transformation. Although these methods are applicable to the special scenarios, there are still shortcomings of their own. Therefore, we propose an approach called two perspective transformations to achieve the real size of objects in 3-D world measurement. Firstly, we use close-range photogrammetry method to obtain 3-D structure of the multiple feature points at the crime scene. Then the 3-D structure will be corresponded to 2D feature points in the measured single image frames, and the collinear equations are used to establish the perspective transformation between 2D features in the measured image frame and 3-D structure in 3-D real world. Finally, we use the perspective transformation matrix to reconstruct the 3-D structure of any feature point in the measured image frame. The method we proposed is successfully applied in a corpse-dismantling case for measuring a box’s height.