not realistic...

I'd guess it's a matter of HDRR (High Dynamic Range Rendering) (see this for an example of the difference between non-HDRR and HDRR.

Well, it's more than HDR. You need to change your lighting model to take into consideration all of the extra lighting which the real picture displays.

The Earth texture has fairly flat colour; it's probably been adjusted to be more uniform, as it's composed of many satellite photos. The ocean in the real-life picture is reflecting a lot of light. The land masses are reflecting a fair bit, too. Your simulation looks flat and kinda dark. There's a specular component in the real photo, off the coast of Australia. Perhaps you could create a specular map, with oceans as areas of high specularity and land masses with less of a contribution?

The land masses in the real picture look slightly desaturated (perhaps a consequence of the brightness of the ocean and the clouds)? Also, there is a lot of contrast between the clouds and the ocean. Maybe that's something HDR could help with.

I think the atmosphere is slightly blurring the outlines of the land masses in the real picture (or it could be the camera). Perhaps some simulation of this?

I also notice that the fall-off from night to day is much, much more defined in the real picture than in yours, and absolutely none of the Earth which is shadow is visible in the real picture. Maybe you could tweak your lighting to move much from night to day in a shorter range, and become 0 after the night threshold?

Your simulation looks good already, I look forward to seeing it with more lighting effects added [smile]

I would add a specular map as suggested: IIRC most places that provide a texture map of the earth also provide a specular (and a bump sometimes) one. Then clouds should be a bit brighter and you should add some kind of atmosphere. Finally, you may think to modify the color of the water, if the previous things aren't enaught.

Personally, I like the first one better, the other one looks too bright...

It probably has more to do with the brighness of your image map. The real Earth picture was probably taken when the camera was between the sun and the Earth. Your texture map is probably composite image, the creator might have 'toned down' the color to hide picture boundaries. The real Earth image is manyly white clouds, which would up the brightness some too. I've also noticed that you have some ambient light in your image, which doesn't exist in space (the real Earth is completely black on one side).

In your shader you should implement a more accurate bidirectional reflectance distribution function.

Google search for Earth BRDF.

Maybe look into the Minnaert BRDF, which was an attempt to create a BRDF that modeled reflectance from the moon. It should be somewhat similar.

Well I'll second the previous statement that the first image looks far nicer. Furthermore, I'd deem what is visually pleasing to be far more important than technically accurate. However, if you do simply want your earth to look more like the real-world shot I don't think you'll want to go much further than altering the textures in something like Photoshop. If you're not comfortable doing that yourself you could post the files and ask really nicely.

Textures have nothing to do with it... unless you're going to be looking at it from the same position every time.

Your textures look fine. The problem is that Earth doesn't reflect light like a perfectly smooth sphere. You need to ditch the Phong BRDF Gouraud model and replace it with a more realistic model.

To the extent that textures might actually help, you could define a BRDF texture, which allows the clouds to reflect differently than water, and water to reflect differently than land, etc. A texture lookup could determine which BRDF to use.

ADDED: I just realized that you never specified that you were using shaders... I don't think there is any way you can do it without a shader. You have no control over the lighting model in fixed-function.

[Edited by - smitty1276 on January 19, 2007 10:20:59 AM]

First of all: thanks for all the replies!
This app is part of a bigger one that is intended to calculate, in real time, sattelite orbits. This will probably run in not so "new" computers, so the support of shaders is unknown. I do intend, tho, to include shaders and check for support on runtime, unsing them or not.
Btw, how do these compatibility issues work? if I try to run an ogl app with glsl shaders on older graphic cards, they simply wont work? or they might work?

Thanks again

Quote:

Original post by FreJa Btw, how do these compatibility issues work? if I try to run an ogl app with glsl shaders on older graphic cards, they simply wont work? or they might work?

Nah, GLSL just plain won't work on GPUs which don't support OpenGL 2.0. You can use GLee to check for specific OpenGL versions (it also sets up all OpenGL extensions, too).

If you want to provide fallbacks, you can use Cg with CgFX files to target specific platforms, from the latest profiles like nv40, etc. right the way back to fixed function. Cg has actually just had GLSL vertex and fragment profiles added (although they're a bit buggy, I hear), so you can actually take advantage of the latest hardware.