CHENNAI: Well before Chinese President Xi Jinping’s convoy wound its way from Chennai airport to his hotel and later to Mamallapuram on Friday afternoon, police had 3D visual information on virtually every rock — if there was any — on the route. Enabling this high-precision surveillance along 50km were four drones designed by Anna University.“These fixed-wing drones can map with a spatial resolution of 3cm, compared to Google Street view map that has a spatial resolution of 60cm,” said an official. “This means anything that is of 3cm could be captured as an image, which includes things inside a parked car on the route.”This aerial surveillance was augmented by six more ‘quadcopter’ drones that provided live visual feed to police control centres manned by Tamil Nadu Special Task Force (STF). Anna University researchers, who were not told about the exercise till the last moment, were asked to train the commandos.More than 30,000 high-resolution pictures, each at 14 megapixels, were shot from an altitude of 100m using these drones over 10 days. A backend team stitched all this together to create an ‘ortho map’ (or a digital surface map). This was later converted into 3D visuals that were fed into a mobile app only the security team could access.“This helped police in identifying vulnerable points and decide on personnel deployment,” said K Senthil Kumar of Centre for Aerospace Research, Madras Institute of Technology, Anna University.Security personnel were stationed on terraces along the route, besides at metro rail stations that are vantage points. On the ground, four officers in the rank of DIG and 16 SP-rank officers have been leading a team of 10,000 police personnel to monitor security of the visiting dignitaries. Three SPs are coordinating with internal security officials and Chinese security officials, with assistance from six assistant commissioners of police, 16 inspectors of police, 48 sub-inspectors of police and 400 other personnel.A quick reaction team (QRT) is stationed at the airport. Another group of three SPrank officials are in charge of the periphery of the hotel in Guindy, where Xi is staying. As many 60 as QRT members have been deployed at the hotel.Two DIG-rank officials, eight SPs, 30 ACs, 90 inspectors and 270 SIs have been deployed along with 3,000 police personnel on the East Coast Road till Muttukadu outside the city limits. The rest of the personnel have been stationed in and around Mamallapuram. After finalising the routes to be taken by PM Narendra Modi and Xi, police have also worked out three contingency routes.