Strange Problem Camera-Matching to Vertical Orientation Photo

[JAFoley]

So we are using a vray camera to match our model of an existing parking lot into a photo of the parking lot. We shot in RAW so we know it was taken at 18mm but on a crop-frame sensor so we should use a focal length of 27.46 to be exact. Well, with these settings, our match isn't even close. It wasn't until I put the focal length at 42mm that everything matches perfectly (camera location, light poles, parking islands, etc).

 

So this makes no sense to me. How can the focal length of the vray cam be so far off of the actual photo? The only thing that I can think of is that the photo was taken in vertical orientation. My vray cam isn't vertical orientated. I'm using the output resolution to make the frame vertical. Could I be correct that my vray cam is essentially having to zoom in on the vertical orientated frame forcing the focal length to be larger? Has anyone had to deal with this issue?

 

Thanks for any incite!

Jared

[JAFoley]

Ok so it looks like my suspicion was correct. For those running into this same issue, here is my solution, but please feel free to comment.

 

If you are matching a vertical orientated shot, input your photo dimensions for the render output. Then take your vertical dimension and divide by your horizontal dimension. This number will be the zoom factor. Lastly, take the focal length that the photo was taken at (correcting for crop-frame sensors if necessary) and multiply that by your zoom factor. This will give you the proper focal length for your 3d camera to match into a vertical orientated photo.

[Corey Beaulieu]

Makes sense. From Spot 3d: Film gate - specifies the horizontal size of the film gate in millimeters. Note that this setting takes into account the system units configuration to produce the correct result. Vertical film gate size is calculated by accounting image aspect ratio (vertical film size = horizontal film size / aspect ratio).

[salvador]

Yep! I've had this problem before. Since I've done this for medium size houses only, I usually guess it on the fly (not happy about it). Thanks for this input, it will be valuable.

 

Cheers!