Prework for heightmaps?

[Mahnmut]

Hello there,
I´ve got a problem with my heightmaps.
I am trying to use a bumpmap from the celestia motherlode to cover a realistically scaled Mars.
My problem is not the spherical projection, I did that by using the bumpmap as displacement image, it works.

But even the biggest bumpmap I could find has one-pixel artifacts that appear as kilometer-sized bumps on my surface.
Could get rid of those by using a "selective gaussian blur" in gimp.

Biggest problem that remains is that -even without this blur- steep features like parts of the valles marineris system appear as rather flat slopes because even a steep grayscale gradient in the map represents some distance on planetary scale.

Has anybody any Idea how to solve this without painting it pixelwise by hand?
Best regards,
Jan

[Arandil]

You need a higher resolution map, and then you'll still have to cover up the artifacts with procedurals.

Even an 8k by 8k pixed image isn't going to get you detail resolution on a planet sized body.

[Mahnmut]

I think I can handle the artifacts.
Any idea where to get a bigger map?

[Arandil]

For free?  Hmmm ... search Google and Yahoo Images.

The image maps at the web site linked below are, I believe, the ones used in the Orbiter simulation, which uses a max of 32k x 16x image maps, but they cost money.

http://planetpixelemporium.com/planets.html

EDIT:

Did some quick searches, here's a few links:

http://www.vendian.org/mncharity/dir3/planet_globes/
http://maps.jpl.nasa.gov/ <-- looks like only small maps, I thought they had larger ones, can't recall offhand

[Mahnmut]

Thanks Arandil!
I didn´t find this mentioned 32k map though, which would be an improvement indeed.
The map I am using now is 16kx8k.
But maybe I will have to wait with that until my ram can handle those big maps anyway.
Could be difficult with my actual pc.
Until then I´ll try to "prework" my maps as well as I can.
Best Regards,
Jan

[Arandil]

Thanks Arandil!
I didn´t find this mentioned 32k map though, which would be an improvement indeed.
The map I am using now is 16kx8k.
But maybe I will have to wait with that until my ram can handle those big maps anyway.
Could be difficult with my actual pc.
Until then I´ll try to "prework" my maps as well as I can.
Best Regards,
Jan

I'm not sure if the 32k maps are on any of those sites.  I only know that Martin (the Orbiter developer) managed to develop 32k maps from online resources, that may have been NASA images.  He implements the 32k maps as many .dds format-based image tiles, of 512x512 size, I think.  It should be possible to extract these tiles and make your own composite texture map out of them, but Orbiter doesn't (currently) leverage bump maps, so you wouldn't be able to get 32k bump maps out of it, anyway.

Good luck!  I've been alternately toying with generating large image maps from other software (Fractal Terrains, Wilbur, ad nauseaum), and also playing with the Power Fractal shader to cook up the equivalent to image masks procedurally, but I'm still taking baby steps (not much time to do anything but read and occasionally reply to posts).

Cheers