'[bo wrote:']I think that's because the images get remapped (warped) on a sphere
KJJones1974 wrote:1. Is the Panorama focal length more accurate than that in the EXIF data?
KJJones1974 wrote:2. Does the FOV figure in the panorama relate to the panorama focal length (not to that in the original EXIF data)?
KJJones1974 wrote:3. When the panorama is not 360 deg, can a focal length be imposed on the panorama (e.g. can I force it to try to create a panorama with the original EXIF data focal length)?
KJJones1974 wrote:As an overview of my problem, I need to be able to calculate the viewing distance of a printed version of the panorama (at a given print size) to replicate the size of the objects as closely as possible when seen by an individual with the naked eye at the place the photographs were taken. To do this, i need to know what the focal length is. Therefore i need to know whether the panorama focal length or the original photograph focal length is the more accurate focal length to use for this purpose.
KJJones1974 wrote:I want the 'scale' to remain the same across and up/down the print, as if the viewer of the print was inside a ball and the inside of the ball was printed withe the panorama (although only 360 deg horizontally). Effectively, such that the viewer can look at any part of the print (at the same distance) and the scale will be accurate - therefore I assume that spherical projection is the most suitable, rather than planar?
KJJones1974 wrote:Does this sound like a sensible way to indicate the most 'trustworthy' focal length for the purposes of calculating the viewing distance of the print?
I want the 'scale' to remain the same across and up/down the print, as if the viewer of the print was inside a ball and the inside of the ball was printed withe the panorama (although only 360 deg horizontally). Effectively, such that the viewer can look at any part of the print (at the same distance) and the scale will be accurate - therefore I assume that spherical projection is the most suitable, rather than planar?
leedsjoe wrote:I think Alexandre's post is saying that the focal length that the user finds in the data in APG is not an input value but an output one. APG algorithms use the input data available (from the images and the EXIF data, if there) to "minimise the visual error". When that process has finished APG records the calculated focal length that corresponds to that minimum.
leedsjoe wrote:If I have got this right then when APG's algorithms change - say between versions, it may well be that the calculated focal length also changes.
But the aim of the exercise is to get the 'best' panorama produced given all the data available which may or not result in the input focal and output focal being the same.
KJJones1974 wrote:As i want to be able to obtain accurate FOVs and focal length figures AND a 'visually nice' result (I want it all i know!), i can see that i will need to always produce 360deg panoramas.
AlexandreJ wrote:The focal estimation is really a hard job when having partial panorama. A small variation of focal doesn't affect at all the RMS. The optimizer really needs a large variation of the focal to see that in the focal dimension, it reached an optimum.
In practice, the result of that is some variation of the calculated focal compared to initial focal given by the camera. This variation is small when beeing at the non parallax point, and can be large when shooting handheld.
Most of time, it doesn't affect at all the quality of the stitch. In fact, it may even help to compensate the parallax caused by handheld photography. What we solves when doing camera estimation is finding the pose that minimize the visual error. If the optimize answer is a longer focal, let it be that way, because the calculation says that globally, the matching quality is better by using this focal.
This debate is totally not true when talking about a 360° panorama. The closure of the panorama pushes an extremely strong constrains on the focal and here, the only answer to the "minimize the visual error" is the real focal length. No other solution here.
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