I have recently made some tests with compensation of atmosphere 
influence in satellite images.  The problem of most high resolution 
satellite images is that the color is influenced differently by the 
atmosphere in different regions of the image and the same surface color 
therefore appears as a different color in different areas of the image. 
  The approach i took is to simply calculate the atmosphere thickness 
for every point of the image from the corresponding height and use that 
for compensation.  More details can be found on:

http://www.imagico.de/pov/earth_atmosphere.html

Attached are two renders from the alps, the first without the 
compensation, the second with it.  Data sources are various Landsat 
scenes for the texture and SRTM + void filling from 
http://www.viewfinderpanoramas.org/ for the elevation.

Other renders using the technique can be seen on the Views-of-the-Earth 
site (http://earth.imagico.de/new.php)

An implementation of the algorithm is available as well but this is not 
a very user friendly program, just a demonstration.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 04 May. 2006)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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Attachments:
Download 'alps2_a1.jpg' (189 KB) Download 'alps2_a2.jpg' (162 KB)

Preview of image 'alps2_a1.jpg'

Preview of image 'alps2_a2.jpg'

Christoph Hormann <chr### [at] gmxde> wrote:
> I have recently made some tests with compensation of atmosphere
> influence in satellite images.

The results are quite noticeable, even on the preview images. It's amazing
to see how much yellow-brown gets turned to green by the atmosphere.

Well done yet again, Christoph. And these are only preliminary results...

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PM 2Ring wrote:
> 
> The results are quite noticeable, even on the preview images. It's amazing
> to see how much yellow-brown gets turned to green by the atmosphere.

Actually the atmosphere has a mostly blue influence.  The overall 
difference in color between the two images is partly due to different 
color balancing which has nothing to do with the atmosphere 
compensation.  The compensation is mostly visible from the color 
difference depending on altitude.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 04 May. 2006)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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Christoph Hormann <chr### [at] gmxde> wrote:
> PM 2Ring wrote:
> >
> > The results are quite noticeable, even on the preview images. It's amazing
> > to see how much yellow-brown gets turned to green by the atmosphere.
>
> Actually the atmosphere has a mostly blue influence.

Well, blue + yellow = green ...

> The overall
> difference in color between the two images is partly due to different
> color balancing which has nothing to do with the atmosphere
> compensation.  The compensation is mostly visible from the color
> difference depending on altitude.

Now I get it. (I think :). So eventually your software will be able to give
the correct atmospheric compensation for any altitude? This sounds like it
could be complicated, since the atmospheric density varies quite a bit over
space and time.

If descending in an anim, will we need to use multiple image map files, or
will we be able to apply the required compensation by applying a correction
function to the image_map in SDL? I suppose the multiple map method will be
much faster than doing it in SDL.

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PM 2Ring wrote:
>> Actually the atmosphere has a mostly blue influence.
> 
> Well, blue + yellow = green ...

Actually - no.

> Now I get it. (I think :). So eventually your software will be able to give
> the correct atmospheric compensation for any altitude? This sounds like it
> could be complicated, since the atmospheric density varies quite a bit over
> space and time.

This is a very simplified model.  As outlined on the page i linked to 
more complex compensations taking into account spatial differences in 
the atmosphere density would require additional data and further 
assumptions about the surface properties.

> If descending in an anim, will we need to use multiple image map files, or
> will we be able to apply the required compensation by applying a correction
> function to the image_map in SDL? I suppose the multiple map method will be
> much faster than doing it in SDL.

I have no idea what you are talking about.  This has actually nothing to 
do with POV-Ray, it's about processing of images.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 04 May. 2006)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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Christoph Hormann <chr### [at] gmxde> wrote:
> PM 2Ring wrote:
> >> Actually the atmosphere has a mostly blue influence.
> >
> > Well, blue + yellow = green ...
>
> Actually - no.

Ok. You're the expert. I just assumed subtractive mixing, like with paints.
Whereas yellow through a simple blue filter looks grey.

> > Now I get it. (I think :). So eventually your software will be able to give
> > the correct atmospheric compensation for any altitude? This sounds like it
> > could be complicated, since the atmospheric density varies quite a bit over
> > space and time.
>
> This is a very simplified model.  As outlined on the page i linked to
> more complex compensations taking into account spatial differences in
> the atmosphere density would require additional data and further
> assumptions about the surface properties.

Ok, I've read your full article now. Sorry, I should've done that before I
started with my comments...

> > If descending in an anim, will we need to use multiple image map files, or
> > will we be able to apply the required compensation by applying a correction
> > function to the image_map in SDL? I suppose the multiple map method will be
> > much faster than doing it in SDL.
>
> I have no idea what you are talking about.  This has actually nothing to
> do with POV-Ray, it's about processing of images.

I'm just talking about using this colour-corrected data in a raytraced,
animated approach to the Earth's surface.  What would one need to do to get
correct planet surface colour when seen at different altitudes?

Thanks for you patience with me, Christoph.

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Hi Christoph,

I just looked to your thread because the headline sounds (and truly is!)
very promising. I also looked to your image.

Now I want to ask you to have a look to one of my images. Please open inside
"povray.binaries.images" (this newsgroup) my thread "SF: Preview 11+: 
Imperial Carrier". It is
all about a starship, with an attached image reflecting the current stage of 
development
of that starship.

I want to ask you, since you develop planetary render scenes, if you are
able to create a planet with clouds as seen - as photo - inside my image.
Moreover, if you can do such things, I want to ask you also if you would
like to work together with me.

Well, and I also would like to invite you to join the project "ISF.RC",
which is all about space and SF (Thread: "povray.general" - "Invitation: POV
Universe").

I would like to have you joining, greetings,

Sven

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Sven Littkowski wrote:
> 
> I want to ask you, since you develop planetary render scenes, if you are
> able to create a planet with clouds as seen - as photo - inside my image.
> Moreover, if you can do such things, I want to ask you also if you would
> like to work together with me.

Thanks for the invitation.  My renders are hardly suited for a realistic 
background in a space scene because they don't include any clouds and 
rendering is both time and memory consuming.

I have already considered creating a free-to-use small scale 
demonstration version with only fairly low detail data and a cloud layer 
but this would hardly be suited for a high resolution space scene.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 04 May. 2006)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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Alright.

Greetings,

Sven

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