用纹理贴图对球体进行凹凸贴图 [英] Bump-map a sphere with a texture map

问题描述

我们想用纹理贴图对球体进行凹凸贴图。但是，球体的表面
的面积是纹理贴图面积的10倍（两个像素的面积）。描述纹理贴图用于凹凸贴图的不同方式。

解决方案

1. 通常矩形纹理用于球体

   
   
   

   纹理（u，v）坐标是用作球坐标的角度。结果是texels在赤道附近较大，在极点附近较小。在极点，所有的纹理元素都合并为单个像素。这是怎么做的

   
   
   
   
   
   • 
     
     
     
     
     
     

     与单光源（Sun）结合使用时，我得到了以下结果：
     $ b p>
     
     

     左侧有
     
     

     等距/纸模型：

     p>
     
     
     
     
     

     等距离：

     
     
     

   
   

We would like to bump-map a sphere with a texture map. However, the surface of the sphere has an area that is 10 times the area of the texture map(area for both in pixels). Describe different ways in which the texture map can be used for bump mapping.

解决方案

1. usually rectangle texture is used for spheres

   texture (u,v) coordinates are used as angles for spherical coordinates. The result is that texels are bigger near equator and smaller near poles. At poles all the texels merge to single pixel. This is how to do it

   • texturing spheres
   • normal/bump mapping

   When you use these maps (color,normal,light,clouds):

   when combined with single light source (Sun) I got this result:

   On the left side with atmospheric scattering and on the right without it. If you zoom a bit you can see the mountains.

2. There are more ways then just rectangular sphere maps

   You can use non linear sphere maps with different properties like eqisurface/distance etc. Here some examples of sphere maps (from google):

   rectangular:

   equidistant/paper model:

   equidistant:

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