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* Spherical projection - 3 messages, 2 authors
http://groups.google.com/group/adobe.photoshop.windows/t/0b1adbe63535b048?hl=en
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TOPIC: Spherical projection
http://groups.google.com/group/adobe.photoshop.windows/t/0b1adbe63535b048?hl=en
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== 1 of 3 ==
Date: Mon, Jun 15 2009 4:26 pm
From: none
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.
== 2 of 3 ==
Date: Mon, Jun 15 2009 5:21 pm
From: Rob
none wrote:
> 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 CS4. Not sure if this is available in CS3
from bridge I open the selected image files into PS layers.
select all layers - them under edit, auto align layers there are
options to join the images and one is spherical.
next auto blend layers.
alternate is to get a panoramic program which also has these options
like , Autopan or PTGui Pro
== 3 of 3 ==
Date: Mon, Jun 15 2009 11:10 pm
From: none
Rob wrote:
>
> I use CS4. Not sure if this is available in CS3
>
> from bridge I open the selected image files into PS layers.
>
> select all layers - them under edit, auto align layers there are
> options to join the images and one is spherical.
Well, CS3 doesn't have the "spherical" option here, but I don't think it
would help. For example, here is what one of my images would look like
(Big Dipper, not my image, but very similar):
http://www.spacetelescope.org/images/screen/heic0716d.jpg
And then here is the chart of that same area in the sky:
http://en.wikipedia.org/wiki/File:Ursa_Major_constellation_map.png
They have very different content.
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