Problems of Forensic Sciences 2018 Vol. 113 (CXIII) 91-104

**CALCULATION OF VIDEO RECORDED VEHICLE SPEED AND DECELERATION AT A CAMERA ANGLE OF 45° RELATIVE TO THE VEHICLE MOTION TRAJECTORY**

**PIOTR KRZEMIEŃ**, **ROBERT GRUŻEWSKI**, **ZYGMUNT WITKOWSKI**

Institute of Forensic Research, Kraków, Poland

**Streszczenie**

The paper is a continuation of an article by the authors on the impact of camera angle relative to the roadway on the uncertainty of vehicle speed and deceleration calculations from video recordings. While in the previous article (Krzemień, Grużewski, Witkowski, 2017) camera orientation perpendicular to the road was discussed, the present paper concerns the results of tests of speed and deceleration calculations for a camera set at an angle of 45° relative to the roadway. In this configuration, greater uncertainties of the calculations were to be expected, as the perspective foreshortening increased, but it turned out that this was not the rule. In order to investigate the uncertainty, data analysis was performed by graphical methods and by comparing 3D images, using the authors’ optimization algorithm operating on the Monte Carlo principle. The speed was measured with a five-Hz GPS receiver and the deceleration with an XL Meter. Due to the fact that the video recording was made with a good quality fixed-frame camera (25 fps), the uncertainties obtained under given conditions could be taken as the lowest. It was found that in general the smaller the camera angle relative to the roadway the greater the uncertainty. The reason was the increase in the perspective foreshortening and the influence of the uncertainty of determining vehicle position relative to the roadway width. The observed decrease in uncertainty of calculations with an increase in the camera angle relative to the road may have been the result of the authors’ gaining of experience in conducting the analysis. Another reason was the reduction in the distance of the camera from the road, which resulted in better visibility of the vehicle.**Słowa kluczowe**Monitoring cameras; Vehicle speed and deceleration; Uncertainty; Image distortion.