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 Post subject: Re: How to correct tilt shift lens to "normal" lens
PostPosted: Mon Sep 17, 2018 9:24 am  (#21) 
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Location: Netherlands
Nutello,

I corrected for the horizon. Starting from one point perspective was no succes, so I repeated the same procedure as above. I studied the tower on different images. I'm almost sure it was square based. So the square is my reference.

find viewpoint:

Image

So now the viewpoint is also corrected. The cyan lines are helplines for the procedure to match the camera with the perspective:

Image

again in blender:

Image

I used this add-on in blender to match the perspective:
https://github.com/mrossini-ethz/camera-calibration-pvr
https://blenderartists.org/t/add-on-cam ... rectangles


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 Post subject: Re: How to correct tilt shift lens to "normal" lens
PostPosted: Mon Sep 17, 2018 8:25 pm  (#22) 
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I totally agree with that yellow horizon line.
I'm not quite sure how you found that principal point. Is it coincidence it's on the horizon? Does that mean the camera was perfectly horizontal?


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 Post subject: Re: How to correct tilt shift lens to "normal" lens
PostPosted: Tue Sep 18, 2018 1:04 am  (#23) 
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Nutello wrote:
I'm not quite sure how you found that principal point. Is it coincidence it's on the horizon? Does that mean the camera was perfectly horizontal?


This property is connected to a two-point-perspective. When the vertical lines are parallel, it is a two point perspective.

In a three point perspective the principal point is not on the horizon. Then there is a perspective triangle. The principal point is the orthocenter of this perspective triangle.

We can know the position of the camera, but we don't know of it is made with tilt-shift, corrected afterwards or cropped afterwards.


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