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Hi,
I use PhotoShop (CS3) for working with astronomy images. I use various types of blending to combine many shots of the same thing.
Once I have the final product, I’m often curious about what some of the more faint spots are. Sometimes I’ll check Wikipedia and compare to their various sky charts, and sometimes I’ll use Google Sky.
The problem is, everyone has different ways of "flattening" their images. The full sky, as viewed by an observer on Earth, is a sphere (or hemisphere, since about half of it is blocked by the Earth). It’s pretty much the same problem as trying to make a map of the Earth fit into a rectangular or square shape. Mathematically, I believe that it is actually impossible to project from spherical to "flat" in a way that conserves area. In other words, you can’t take the surface of a sphere and flatten it out into a rectangular shape without parts of it becoming distorted in some way.
Google Sky images, for example, use a projection that causes the top and bottom to become highly stretched — kind of like the maps of the world that make Greenland and Antarctica look really huge. The charts on Wikipedia are generated from a program called PP3 that apparently uses a different type of projection.
The bottom line is that neither of those two images line up with an actual picture of the sky. And it’s not a simple matter of using the "transform (ctrl-T)" command in Photoshop. I guess you could say that some sort of "non-linear" transformation would be required to convert between the three different types of projections.
Anyone have an idea how to convert between the three? I understand that it won’t be trivial, because it all depends on where the "poles" are and so on… Maybe there is a plug-in to help?
Thanks in advance.
I use PhotoShop (CS3) for working with astronomy images. I use various types of blending to combine many shots of the same thing.
Once I have the final product, I’m often curious about what some of the more faint spots are. Sometimes I’ll check Wikipedia and compare to their various sky charts, and sometimes I’ll use Google Sky.
The problem is, everyone has different ways of "flattening" their images. The full sky, as viewed by an observer on Earth, is a sphere (or hemisphere, since about half of it is blocked by the Earth). It’s pretty much the same problem as trying to make a map of the Earth fit into a rectangular or square shape. Mathematically, I believe that it is actually impossible to project from spherical to "flat" in a way that conserves area. In other words, you can’t take the surface of a sphere and flatten it out into a rectangular shape without parts of it becoming distorted in some way.
Google Sky images, for example, use a projection that causes the top and bottom to become highly stretched — kind of like the maps of the world that make Greenland and Antarctica look really huge. The charts on Wikipedia are generated from a program called PP3 that apparently uses a different type of projection.
The bottom line is that neither of those two images line up with an actual picture of the sky. And it’s not a simple matter of using the "transform (ctrl-T)" command in Photoshop. I guess you could say that some sort of "non-linear" transformation would be required to convert between the three different types of projections.
Anyone have an idea how to convert between the three? I understand that it won’t be trivial, because it all depends on where the "poles" are and so on… Maybe there is a plug-in to help?
Thanks in advance.
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