vertex. Then, the position is interpolated across polygons to which the vertex is attached. This eliminates the need for recalculating every pixel's reflection direction. If normal mapping is used, each polygon has many face normals (the direction a given point on a polygon is facing), which can be used in tandem with an environment map to produce a more realistic reflection. In this case, the angle of reflection at a given point on a polygon will take the normal map into consideration. This technique is used to make an otherwise flat surface appear textured, for example corrugated metal, or brushed aluminium. Types Sphere mapping Sphere mapping represents the sphere of incident illumination as though it were seen in the reflection of a reflective sphere through an orthographic camera. The texture image can be created by approximating this ideal setup, or using a fisheye lens or via prerendering a scene with a spherical mapping. The spherical mapping suffers from limitations that detract from the realism of resulting renderings. Because spherical maps are stored as azimuthal projections of the environments they represent, an abrupt point of singularity (a "black hole" effect) is visible in the reflection on the object where texel colors at or near the edge of the map are distorted due to inadequate resolution to represent the points accurately. The spherical mapping also wastes pixels that are in the square but not in the sphere. The artifacts of the spherical mapping are so severe that it is effective only for viewpoints near that of the virtual orthographic camera. Cube mapping Cube mapping and other polyhedron mappings address the severe distortion of sphere maps. If cube maps are made and filtered correctly, they have no visible seams, and can be used independent of the viewpoint of the often-virtual camera acquiring the map. Cube and other polyhedron maps have since superseded sphere maps in most computer graphics applications, with the exception of acquiring image-based lighting. Image-based lighting can be done with parallax-corrected cube maps. Generally, cube mapping uses the same skybox that is used in outdoor renderings. Cube-mapped reflection is done by determining the vector that the object is being viewed at. This camera ray is reflected about the surface normal of where the camera vector intersects the object. This results in the reflected ray which is then passed to the cube map to get the texel which provides the radiance value