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I have a video camera at a high building (eg. 10 storey high) looking at an area. The video screen is stream to display on my laptop.

If I know a building’s latitude/longitude, how can I calculate what position (in pixels) I can mark out a cross on my display video to indicate the position of the building?

user3790147
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  • This isn't clear to me. Are you trying to mark off on a map where the building is? – Tim Biegeleisen May 24 '16 at 01:17
  • Thanks for the reply! Its not on a map but on the video display which is the camera's point of view. So if the camera is facing the tracked building, but it is blocked off by an object (maybe another building), I would still see a cross on the display which indicates the position of the tracked building. – user3790147 May 24 '16 at 01:44
  • I think you will need some kind of software to handle this. I don't see a quick fix to this problem. – Tim Biegeleisen May 24 '16 at 01:45
  • Could I perhaps get the Cartesian coordinates of the camera and building, and then use perspective projection on them? – user3790147 May 24 '16 at 02:09

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What you are looking for is Augmented Reality.

You would need to know what the focus of the camera which is/was a non-trivial task. I wrote one many years ago for a professional Sony DVCAM system that used error diffusion pulled from Numerical Recipes book. This took a long time to set up and calibrate but once calibrated the focal length was fixed.

Modern systems use a half-cube system in which software knows the size of the cube and thus can infer the focal length, fov and other aspects of the camera. Again not a trivial operation but a lot quicker than my method. I read a paper by a canadian guy who had a virtual tank driving over objects in photos of Greece IIRC. This was in 2001 so forgive me if the name of the paper slipped my mind.

Another aspect you have to consider is the angle and orientation of the camera you have. While you know the GPS of the camera, you need to know the orientation. You can get cheapo electronic compass that will give you the best-guess direction but what you need is an IMU. They can range from a few quid for Arduino ones to many thousands for industrial. Since you have the pull and rotation of the earth as constants you can infer from the strain placed on the axes of the IMU what its orientation is.

The ideas which were difficult then are probably common place now. Your best bet would be to read through some papers on Augmented Reality.

graham.reeds
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