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tech / sci.electronics.design / Re: Help !! Projecting a sun disc onto a spherical hemisphere

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* Help !! Projecting a sun disc onto a spherical hemispherea a
`- Re: Help !! Projecting a sun disc onto a spherical hemispherea a

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Help !! Projecting a sun disc onto a spherical hemisphere

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Subject: Help !! Projecting a sun disc onto a spherical hemisphere
From: manta1...@gmail.com (a a)
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 by: a a - Fri, 7 Oct 2022 12:27 UTC

What image of the Sun I get from a solar telescope is sun disc,
so solar hemisphere is projected to 2D sun disc.
\ I would like to reverse the projecting, taking sun disc as an input

and spherical hemisphere image as an output, to calculate number of sunspots in spherical geometry.

If you know tools reversing
spherical hemisphere to sun disc projection
just let me know or suggest something.

Is Gimp ok ?

Re: Help !! Projecting a sun disc onto a spherical hemisphere

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Date: Fri, 7 Oct 2022 06:32:52 -0700 (PDT)
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Subject: Re: Help !! Projecting a sun disc onto a spherical hemisphere
From: manta1...@gmail.com (a a)
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 by: a a - Fri, 7 Oct 2022 13:32 UTC

On Friday, 7 October 2022 at 14:28:01 UTC+2, a a wrote:
> What image of the Sun I get from a solar telescope is sun disc,
> so solar hemisphere is projected to 2D sun disc.
> \
> I would like to reverse the projecting, taking sun disc as an input
>
> and spherical hemisphere image as an output, to calculate number of sunspots in spherical geometry.
>
> If you know tools reversing
> spherical hemisphere to sun disc projection
> just let me know or suggest something.
>
> Is Gimp ok ?
alike Gimp question

---
Ok, I can add margins to image of the sun disc
to get sun disc projection limited to hemisphere only

Ok, I can rotate image od the sun disc in input 2D image to watch the strech effect at the edges of the sun disc, all around.

https://graphicdesign.stackexchange.com/questions/80701/gimp-flat-image-to-round-ball-surface-sphere

GIMP - Flat image to round ball surface (sphere)
Asked 5 years, 10 months ago
Modified 5 years, 7 months ago
Viewed 17k times
3

Using GIMP 2.8. Trying to map an image to a sphere. The idea is to make custom Christmas balls. In addition to map to sphere, I have tried perspective and cage transform, but with limited success.

2 Answers
Sorted by:
4

Map to sphere is fairly straightforward, the whole width of the image is mapped to the equator and the height is mapped to a meridian, so if you do not want your object to cover the whole sphere you need to add margins. A square image produces a sphere, and since the width of the image is mapped to the double of the height and everything looks stretched 2x horizontally, so you have to shrink horizontally (or strech vertically) first.

---
let me know your opinion.

Ther easiest way is to have live solar image from telescope projected directly onto hemisphere of the spherical ball.

Ok for watching, but hard to make any calculations.

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