I have old photos of a town and landscape around it. I'd like to take these photos again, from the same locations. In some cases I am struggling with finding the original location of the camera.
I can identify objects on the photo, I know their position on the map in some cases even their dimensions, but I don't know anything about camera or lens. Are there any techniques (or even better any ready-made software) to calculate position of the camera from the photo?
Answer
The key is to find areas of the image with a lot of parallax, such as a foreground building and a background tree. Try to pick a point as close to one edge of frame as possible. Now walk left/right (green) to find the correct point of intersection from the old photograph.
Now that you've done that, you've established a straight line to move along (red).
Pick a different parallax intersection on the other edge of frame. Instead of walking left/right, walk along the red axis you established earlier. Once you've matched that parallax, without spoiling the first match, you've found the position of the camera.
Once you're in the same position, matching the lens is easy. You can just look through the camera and adjust until the framing matches, or measure the angle of view.
There is software that can calculate the position of the camera, but generally you need a 3D model of the scene as a basis.
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