A massive security operation is being deployed for the royal wedding with CCTV on the ground and surveillance in the sky.
The royal wedding on April 29 is expected to be watched by more than two billion people, so police are keen to avoid any disruptions.
From a police helicopter, officers can get a better look a problem or individual.
Sgt Richard Brandon told Sky news: “If you’ve got a particular location or potential problem or individual we want to look at, we’ll put it on screen and let the control room have a look.
“You can get detailed images of people, even number plates, and from that the control room can make a tactical decision about what to do next.”
From the moment that the wedding date (April 29) was revealed, police have been building up a picture of weak spots, such as rooftops.
“The police will be engaged in a massive security operation in the weeks leading up to the wedding,” Brian Paddick, the former deputy assistant commissioner of the Metropolitan Police, told Sky News.
“They will be looking at people known to have an obsession with the Royals, perhaps, or people they suspect of planning a terrorist attack, to ensure that security is tight on the day.”
Police annual leave has been suspended for that day.
Ahead of the royal wedding, officers have already began searching drains, lampposts and traffic lights to check for explosive devices.
“Once somewhere’s been searched and deemed safe it will be sealed and checked on a regular basis to make sure it hasn’t been tampered with,” said former public order officer Graham Wetton.
Sniffer dogs are also being deployed before the big day to sniff out explosives.