Photo camera matching help

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Old 05 May 2013   #1
Photo camera matching help

Hi, i havent done much camera matching before and im having some trouble on the image below, the gravel areas going to be grassed over but i cant seem to get the camera in the right place for the plane to match up properly, the area is square. im standing about 30m away from the center of the image and about 4m up, i dont know what the camera focal length is. any help you can give would be great
Old 05 May 2013   #2
Why don't you know the focal length? It's going to be tough to match without knowing it. From your post it sounds like you shot the photo, so why not check your EXIF details?
Old 05 May 2013   #3
If it's just an image, you should be able to just read the EXIF data for the lens. Remember that the focal length is also affected by your sensor size.

Also since you took the photo, dont you have access to the camera? Easy enough to look up what you shot with

If it's just an image, you dont need to track. Just paint it in. If its a video there are a few options:

if you're just painting grass in and the motion isn't crazy, you don't need to do a 3D track. You have enough points in the image to do a 2D track and corner pin the grass down.

If you have access to a planar tracker like in Nuke or Mocha, this is even easier since you can just try and match the perspective down.
Old 05 May 2013   #4
yes i did take it and the exif data says a focal length of 6.2mm, thanks for your help,
although now i think of it, i could have taken 2 photos and used photo sculpt to make a model out of it
and i do have mocha but ive never used it so ill have to look that up

Last edited by Rareden : 05 May 2013 at 02:19 AM.
Old 05 May 2013   #5
6.2mm focal length? That can't be right.
Old 05 May 2013   #6
Multiplier for an APS-C sized sensor in reverse from a ~10mm focal length?

Seems wide but not -that- wide.
Old 05 May 2013   #7
its one of those cheap digital cameras shaped like a box, they didnt have a proper camera and nor do i.
Old 05 May 2013   #8
Ah point-and-shoot cameras can have very small focal lengths because they have way smaller sensors, so that is probably correct.

You can use the combination of that and the sensor size / film back to match better.

Camera Sensor Database
Old 05 May 2013   #9
Hey man,

12mm is a crazy fisheye, 55mm is around what a human might see, and 300mm is an average telephoto lens. Your image looks like it might be around the SLR equivalent of 75mm.

Your image doesn't look like its level, and that might be making it difficult for you to match. Try removing the rotation constraint on the 3d camera, or maybe level out your image in PS. You've also got some distortion.

Old 05 May 2013   #10
i should go get a slr to do this properly
Old 05 May 2013   #11
Originally Posted by AJ1: Hey man,

12mm is a crazy fisheye, 55mm is around what a human might see, and 300mm is an average telephoto lens. Your image looks like it might be around the SLR equivalent of 75mm.

Those are all very much ex 35mm film standards though.
The filmback determines what the focal length corresponds to.

IE: on my GH2 a 12mm is actually the equivalent of 24.2mm on a 35mm film back.
A fish eye is also particularly shaped, so it's incorrect to assume that just because of the focal length a 12mm would be a fish eye, it might very well be simply a super wide angle, or just a wide.

On a cheap, old point and shoot with a high crop 6mm is perfectly possible and might very well be the equivalent of a 24mm on a 35mm film back. Cellphone cameras are pretty much all sub 4mm.

The pitcure in question has plenty obvious escape lines on flat planes, it should be possible to eyeball it with a bit of work against any arbitrary unit of measure in 3D, and most modern tracking software would guess you a decent feed if it was a sequence.
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Old 05 May 2013   #12
What is the camera model? If we know that, we can find out the sensor size and then the multiplication factor.
I like to learn.
Old 05 May 2013   #13
Its this one
Old 05 May 2013   #14
It is a very small sensor, less than a third lengthwise of the MFT standard, which is already a considerable crop.

It's rated as a 37 to 187mm.
Take a couple snaps at its shortest and longest lengths, and see what you get out of the metadata.

I'd say it's a safe enough bet to assume that the 6mm and spare change you got was its shortest, and a 37mm equivalent (to a 35mm film back standard) focal length.
Come, Join the Cult - Rigging from First Principles
Old 05 May 2013   #15
let me get this right, the camera matching is just for a single frame?
ive used syntheyes for this kind of project, it has nice tools to match single frame.
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