Texture coordinate generation : sphere map shape

shphere map shapesphere map shape result

When using a sphere as the map shape, the ( x,y,z ) value of a point is converted into spherical coordinates. For purposes of texture mapping, we keep just the latitude and the longitude information. To find the color in the texture map, the latitude is converted into an x-coordinate and the longitude is converted into a y-coordinate.

The objects have a map shape of a sphere, and the poles of the sphere are parallel to the y-axis. At the object’s "North Pole" and "South Pole", the squares of the texture map become squeezed into pie-wedge shapes. Compare this to a map shape of a cylinder. Both map shapes have the pie-wedge shapes at the poles, but there is a subtle difference at the object’s "equator". The spherical mapping stretches the squares in the texture map near the equator, and squeezes the squares as the longitude reaches a pole.

Source : Teaching Texture Mapping Visually by Rosalee Wolfe / DePaul University / wolfe@cs.depaul.edu