I am doing this for a thesis project. What I am doing is using an
icosadecahedran as my base and then subdividing it as per the OpenGl red
book demo. An octtree is then used to store all of the initial polys. Camera
distance from any given octant is used for visibility determination and to
decide if the poly in the octant is subdivided. If subdivided the new
polys are added into the oct tree. A heightfiel is mapped initialy to the
icasodecahedron vertices and they (the vertices) are displaced as per the
heightmap. When a subdivisin occurs the heighmap bounds the maximum height
in the new terrain. Subdivided terrain also uses midpoint displacemnt to
find the new height (fractal browianina motion). All initial polys have a
seed value, and so do new polys so that the same terrain is generated
independent of the flight path.
On Mon, 3 Dec 2001, Neil McLaughlin wrote:
> You could use a parametric surface for the Earth with cylindrical coordinates (longtitude, latitude).
> It is indexed like a Texture in U,V coordinates (0.0<=U,V<=1.0). You may want to apply a height map for terrain - possibly using the texture itself or a parallel black and white version (Bryce style). This has limitations of not supporting overlap (such as a crested wave or cave).
> It's easy to texture map parametric surfaces since they are grid aligned, but you'll need to dynamically tesselate the portion you are looking at, defined by a rectangular region of the surface (u,v - U,V). The algorithm should zoom to make any such portion fill the screen. Then it's infinitely scalable. However, depending on how far you zoom the texture will get "stretched" because textures (like polygons) are not infinitely scalable. You may want to have each color on the texture represent another texture once you get up close, or use Procedural Textures.
> If you need to use a static mesh of the planets, you'll want Subdivision surfaces or to break them into parametric patches, as polygons are also not infinitely scalable and you need to maintain smooth curvature.
> Neil McLaughlin
> ----- Original Message -----
> From: Julien JEANY
> To: Game Dev Algos
> Sent: Monday, December 03, 2001 12:46 PM
> Subject: [Algorithms] Generating landcape
> Thanks for your answer.
> In fact what I want to do is a planet-body generator integrated with a
> texture generator.
> My planet musts become more complex when my camera becomes nearer. I think I
> should do my render with some octrees, to increase the time of rendering.
> I don't know how to do that, so if you can help me... =)
> Thanks to take time to answer me.
> Good luck, and excuse me for my (very) bad english.
> Julien JEANY aka blaine
> EPITA - Spe B2 - Promo 2005
> -= Protect your human right to party =-
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