Yesterday I'd implemented the skybox exporting and procedural planetary textures exporting feature. Here I'll show examples of the interface dialogs and examples of exported textures. I've also added a new "projection" mode - displaying of a skybox.
This is of a procedural planet:
And this is the skybox capture interface (it is fully real-time and also avaliable through the Projection settings dialog):
You can choose any resolution that is supported by your graphics card (8192 for my GF9800GTX, but trying to set it to more than 4096 had crashed my video driver ). Image format can be choosen via config as for regular screenshots.
Link to example skybox: http://en.spaceengine.org/upload/skybox.zip ADDED: Hi-quality version: http://en.spaceengine.org/upload/skybox-hifi.zip It was captured in 2048 x 2048 resolution and then reduced twice to perform "fake antialiasing".
Next is the textures exporting interface. You can export textures in two forms - cylindrical projection (it is used in SE for base "-1" level for planets) and cubemap projection (default SE format), but only for a zero level. However, you can choose any resolution that your graphics card can support, like for the skybox exporting. You can choose which layer you would like to export (surface and/or one to three clouds layers) and which texture - color map, heightmap and normalmap.
Here are the examples of cylindrical surface map and elevation map of this planet:
Link to other textures in cylindrical projection: http://en.spaceengine.org/upload/cylindrical_textures.zip Link to textures in cubemap projection: http://en.spaceengine.org/upload/cubemap_textures.zip
It is not difficult for software to add exporting for any level, but it is performance and "interface" difficult. And what can they be used for? Finest levels of typical procedural planet has a total of 1 million x 1 million pixels resolution (1 terapixel ) and will be 15 terabytes in size (or 4096 x 4096 = 16777216 tiles of 256 x 256 resolution). I think only the few first layers can be useful in another application. Some tiles of very detailed levels can be used as independent heightmap for creating a map for example for some other games, so I may add an interface feature someday (such as click on a mountain and choose "export heightmap and textures").
UPD: SpaceEngine saves exported textures in the cache/export folder. Old files are overwritten, so make sure you save them before making a new export.