Relative position of latlon points

Question

I'm currently involved in a project where it'd be useful to display geographical points as overlays on top of a VIDEO element (size 512x288).

The VIDEO element contains a live broadcast, and I also have a real time feed of bearing, latitude, longitude and altitude that's fed into the site as JavaScript variables.

I also have an array of POI's (Points of Interest) that's included in the site. The POI's are in the following format:

var points = [['Landmark name', 'latitude', 'longitude'], […]];

Every five seconds or so, I want to loop through the array of POI's, and check to see if any of them are within the video's current viewport - and if true, overlay them on top of the VIDEO element.

Could someone point me in the right direction as to what I should be looking at? I assume I have to map the points to a 2D plane using e.g. Mercator projection.

But I'm a bit lost when it comes to mapping the POI's relative pixel position to the video's.

Looking forward to getting some tips!

Answer 1

Having done this before, the most critical element is to determine the field-of-view of the camera accurately (at least to the hundredth of a degree) in either the vertical or horizontal direction. Then, use the aspect ratio (512/288 = 1.78) of the video to determine the other angle (if needed) using atan formula (do not make the common mistake of multiplying the vertical field of view by the aspect ratio to get the horizontal field of view. Field of view is angular, aspect ratio is linear). Think of it in terms of setting up a camera, for example, in OpenGL except your camera is in the real world. Instead of picking field-of-view and camera orientation, you are going to have to measure it.

You will need to know the attitude of the camera (pan/tilt or pitch/roll/yaw) in order to overlay graphics properly.

You won't need a Mercator projection. I am assuming that the field of view of the camera is relatively small (ie. 40 deg H or so) so you can usually assume the projected surface is a rectangle (technically, it is a small patch from a sphere).