Wrong values at screentosphere??

  • Hi everyone / Klaus,
    I'm trying to get the exact (horizontal) mouse-coordinates at distortet hotspots. My assumption: A hotspot with 500px width should be displayed with a width of 45°. This is working fine. So the left and right edge of a hotspot (centered at 0°/0°) sould be -22,5° and +22,5°. But when I try to get the mouse coordinates over the left and right edge of the hotspot via screentosphere, it indicates a Position about -26° and +26°.

    I tried also to check this with the tools from tuur. The hotspot is shown perfectly in the grid, but when i hover the mouse to the left/right corner of the hotspot, mouse_ATH is again around -26°/+26°.


    The mouse_ATH (calculated via screentosphere) at the 15° grid is about 18°, at the 30° grid mouse_ATH ist around 33°.Is there anything wrong in my asumptions? Does anybody know, how to get the correct mouse coordinates?
    Thanks a lot for your help....

  • I'm not sure if my understanding is right, so I made an example here:
    https://argum.video
    If I hover over the the left/right edge of the green Hotspot, the ATH-value should be -22.5°/+22.5°???
    I tried to visualize my understanding here: Could anybody tell me what is wrong in my understanding??

  • The means reason is the that coordinates are simply spherical...

    In your example you have split the flat cube side image linearly into equal parts, but a spherical projection is not linear.

    E.g. a 45°fov with a 1000px base would be 414px (not 500px).
    500px would be ~53 degree fov (not 45 degree)

    E.g. here the base formals:
    px = tan(fov/2 * PI/180) * 500 * 2
    fov = 2 * arctan(px/2 / 500) * 180/PI
    (the 500 is the 1000/2 base)

    Maybe draw a circle and box around it, make a line in the middle, and the try to find the angles and lengths using trigonometry.

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