Mapping an image on sphere and getting back the unwrapped equirectangular projection

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Hi,
I'm trying to achieve the following task:

Imagine having a 2:1 aspect ratio drawing canvas. I want to place rectangular images on this canvas (..x,y Cartesian coordinates) and as I move the image around further away from the canvas center (0,0) I want to get the distortion to the image as if it was sliding over the imaginary sphere's normals.

The logic I believe is to convert the (x,y) 2D Cartesian coordinates of the image to the corresponding latitude, longitude spherical coordinates, and then apply the equirectangular projection to the sphere and return the image with the corresponding distortion (as if it's uvs where unwrapped in a 3D modeling package).

There is an application doing exactly that called "HDR Light Studio" which generates equirectangular (lat/long) HDR images for 3D scene lighting purposes.
If you check out their videos you will understand exactly what kind of image distortion I'm trying to achieve.

Please give me some help over the subject if you can.
I have searched all around the net for info but no luck.

Thanks in advance

--Edit-----------------
I have found an interesting article here at CodeProject:
http://www.codeproject.com/KB/graphics/PolarView.aspx[^]

The logic is very close to what I'm trying to achieve but not exactly.
Again, if someone can take a look at "HDR Light Studio" videos from their site will understand exactly what kind of real-time image distortion I'm trying to achieve.

Posted 16-Nov-10 7:41am

skokkinos

Updated 16-Nov-10 10:02am

v4

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ely_bob 6-Dec-10 13:00pm

Are you still looking... ?

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ely_bob · Answer 1 · 2010-12-06T08:20:00

Well.. since I'm compiling... :laugh:

there are a couple of ways to do this... that i can think of.. the best is up to you to decide...

First you will want to make a decision about weather your looking for a fisheye effect or an actual projection, because it isn't exactly clear...

However.. I will proceede like a blind man..

If you want Fish eye... You will need to find the mapping of a curved surface to a square.. (probably easiest to do this in polar coords) there are a lot of these references available on graphics and physics websites... basically what you need to "fudge" is the granularity of the points to which you want to do interpolation...

For a sphere inside a cube, you repeat the previous approach 6 times...

the example you referenced is for a circumscribed circle over a flat surface, as opposed to an inscribed sphere being projected upon from a flat surface... or a sphere projecting onto a surface, as opposed to a
sphere unwrapped (UV style) and placed on a surface...

I hope that helps..?:confused:

If you have the Exact URL of a screen that shows what your looking for it is better to post that then say .."take a look at 'HDR Light Studio' videos from their site"...this isn't very helpfull... :doh: