[FFmpeg-trac] #9376(avfilter:closed): Wrong conversion from flat to equirectangular

[FFmpeg]

#9376: Wrong conversion from flat to equirectangular
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             Reporter:  jumpjack  |                    Owner:  (none)
                 Type:  defect    |                   Status:  closed
             Priority:  normal    |                Component:  avfilter
              Version:  4.3.2     |               Resolution:  wontfix
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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Comment (by Michael Koch):

 Replying to [comment:11 jumpjack]:
 > This looks like a double bug to me:
 > - FFmpeg ignores the keywords "pitch" and "yaw" and do what it likes
 with the numbers

 The v360 filter does exactly what it's supposed to do.

 > - FFMpeg introduces a roll upon changing only yaw and pitch; the order
 of the rotations should not matter, yaw=10:pitch=10  and pitch=10:yaw=10
 should give same rotation, without adding any roll.

 Sorry, that's wrong. We are talking about a spherical coordinate system,
 like the geographical coordinates on earth.
 Case 1: You walk 1km north, then turn 90° left and walk 1km to the west.
 Case 2: You walk 1km to the west, then turn 90° right and walk 1km north.
 You might think that in both cases you arrive at the same place. But
 that's wrong.
 It becomes clear when you walk longer distances:
 Case 3: You start at the equator in Africa and walk north until you reach
 the north pole, then turn 90° left and walk the same distance. You will
 arrive somewhere in central America.
 Case 4: You start at the equator in Africa and walk west until you are in
 central America, then turn 90° right and walk the same distance. You will
 arrive at the north pole.
 That means the order of rotations is important.
 When you have made yaw and pitch rotations (in this order) and want to
 undo these rotations, you must undo them in reverse order. First pitch and
 then yaw.

 Michael
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Ticket URL: <https://trac.ffmpeg.org/ticket/9376#comment:12>
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