Wireframe Rendering


   Wireframe rendering is the fastest, yet crudest form of 3D rendering.
   In fact, many of the charactoristics of three dimesions are lost when
   rendered using this method. The main advantage of using wireframe
   rendering is it's very fast speed. From the standpoint of the
   computer, it is the simplest method of rendering in which lines are
   drawn from every vertex to every other vertex which it is connected
   to.
   
   Typically, wireframe rendering is used as a quick way of previewing a
   model, and isn't generally used in the final rendering. Most, if not
   every, 3D modeller is capable of wireframe rendering. Some only offer
   it in the modeller and not in the renderer.
   

--------------------------------------------------------------------------


        			Constant shading
                                      

   Flat surface rendering (or 'constant shading') is the simplest
   rendering format which involves some basic surface properties such as
   color distinctions and reflectivity. This method is exclusively used
   on polygon models, such as Strata Vision, to produce a rendering which
   has nothing done to 'smooth' over the facets which make up the
   surface. The resulting visualization shows an object which appears to
   have surfaces faceted like a diamond.
   
   From the stand point of the computer, this method of rendering only
   requires computation of a color for each visible facet. The whole
   facet then is filled with this color. Images can be produced fairly
   quickly this way than otherwise more complicated methods.
   

--------------------------------------------------------------------------


               			Gouraud Shading

                                      
   Gouraud shading is the next step of realism after flat surface
   shading. Gouraud shading uses the information attained from flat
   surface shading and linearly interpolates the color shade of one
   surface normal to other adjacently connected surface normals. The
   result is a much smoother looking sufaces on rounded objects at the
   price of a moderate increase in rendering time. A drawback to Gouraud
   shading is the occational presence of artifacts around polygon edges
   and around areas of specular highlights. Gouraud shading is available
   in Strata Vision as an intermediate rendering step between quick
   previewing and final proofs.
   

--------------------------------------------------------------------------


				Phong Shading

                                      
   Phong shading is similar to Gouraud surface shading, but instead of
   color being interpolated from polygon normal to polygon normal,
   normals are interpolated. The result is a larger number of normals,
   each corresponding to a pixel in the viewing plane (i.e. the rendering
   window). The resulting normals are then used to calculate the color
   shades. This results in renderings similar to Gouraud shading, except
   reflections on the surface of the objects are sharper and more
   defined. The main advantage, though, of Phong shading is the ability
   to 'tinker' with the surface normals with surface maps and
   enviromental variables to further increase realism. Again, this
   technique is used exclusively for polygon based models, and is the
   most realistic surface map rendering technique currently available in
   commercial rendering packages.
   


---------------------------------------------------------------------------


                             Radiosity Shading

                                      
   Radiosity shading is a rare rendering method primarily used for
   animation purposes. It works by altering surface maps on an object to
   properly realize the amount of light which that surface is reflecting.
   The result is a model which can be rendered quickly (such as with flat
   surface shading) but looks similar to a ray traced image (shadows,
   textures, etc.). The advantage of this is to quickly render 3D
   animations 'on the fly' which have very quick rendering times with
   realistic lighting attributes. A common drawback to radiosity is the
   appearance of 'dull' non-reflective surfaces. This is due to the fact
   that any reflections (e.g. a light source seen through a mirror)
   depends on the point of view of the rendering. In general, any point
   of view dependant charactoristics are severely hampered, such as
   shadows produced by the 'camera', reflections, surface glossiness,
   texture bumpiness (unnoticable in small textures), etc.
   
   Radiosity is very common on Silicon Graphic machines (SGIs) where 3D
   'spinning' engineering models are a common-place. (SGIs are generally
   very fast at surface mapping). Another form of radiosity is common in
   video games such as Marathon or DOOM. This is actually debatable
   whether these games actually used radiosity since it is likely that
   some (if not all) of the surface map 'rendering' was done by hand.
   But, never-the-less, they do render pre-shaded surface maps on the fly
   using a fast renderer such as flat surface shading.
   
   There is a simliar rendering method in Strata Vision Pro called
   'Raydiosity' (note the 'y'). This has some similarities to radiosity,
   but is used as an alternative to ray tracing. From what I have heard,
   it produces dull textured objects with more realistic 'fuzzy' shadows,
   and tends take something on the order of ten times longer than normal
   ray tracing. This isn't used for quick animating as described above
   and is quite different from 'real' radiosity.
   
.