difficulties with alining 3d objects with tracked footage

Support Compositing and Post Processing
1

so i tracked this footage i made with my mobile phone: http://www.screencast.com/t/oqnMD2lT . as you can see the tracking is almost OK, but what bothers me is that i cant line up that cube proberly with this building. i cant seem to match it perspective wise.

according to specs, my phone cam has a fov of 25mm and a sensor size of 1/2.3" which is apparently 6.17*4.55 mm. so technically the fov should be correct like this. but it isnt. i also tried out manually increasing the fov of the camera, but even though it may line up better on the right side of the cube, it starts to not fit at some other part.

not sure what I’m doing wrong.

here’s the blend file, in case anyone wants to look into it (it’s 0.9gb though because of the clip).

2

The 25mm fov is most probably the full-frame sensor equivalent. 25mm for your sensor would be a telephoto zoom already.

You can calculate the approximate (25mm is an approximation most probably) actual fov like this: fov = 25mm * (6.17mm / 36mm)
It comes to ~4.284 mm. Try this with your sensor size.

Other option would be to set your sensor size to 36x24mm and use fov 25mm.

3

thanks, but blender already did this by itself. i entered the 25mm, then the sebsor size. upon that blender changes the fov to indeed 4.something. so this cant be the issue (will still try with your number when I get home, i think blender did 4.1something)

but the way to fix this would generally still be to play around with the fov?

4

If the perspective seems not right then either object is in wrong place or fov is wrong. In your footage the fov is off. I would say it is too wide by the looks of it.

BTW, are you sure the building itself is rectangular?

It could also be that the video footage is not recorded from full sensor width, but cropped. In that case good luck finding what the real used width is. You can dig in the net, maybe you’ll find something.

5

use the blam addon on one of your frames to get the camera info then just copy that info into your tracking blend. its usually pretty good at working out the correct camera settings

6

thanks, that blam addon seems to work pretty well, in terms of camera positioning and approximating the fov. turns out my full-frame fov is a bit less than 25mm

7

Beware of in-camera stabilization as well. It may zoom the image a bit and change the centre of frame, making the reconstruction fail.

8

good point. do phone cam apps do this by default? because i couldnt find any options like this to turn off in both my phone apps.