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View Subdivision Surface

A Subdivision Surface (SubD) is any polygonal surface that has then had an effect applied that “smoothes” the original surface by adding more resolution (more polygons), and modifying the final surface shape by analyzing the contributing polygons from the original surface.  The final shape is extremely dependent upon the polygonal distribution of the source surface.  Evenly-spaced polygons on the source surface will yield an even mesh in the SubD surface. Oddly-distributed polygons on the source surface can yield strange, perhaps even unusable results on the SubD surface.  Areas of high polygon density on the source surface will be jammed with polygons on the SubD surface.  In practice, should you have a large area covered by a few polygons transition into many polygons that are densly packed, you will see a noticable affect on the SubD mesh.  This may also impact the fidelity of your image maps and procedural shaders at render time.

SubD modeling is the most common modeling technique used today, and that has been true since they were introduced into the computer modeling lexicon.  A good idea is a good idea, and the ability to originally create a low resolution, nee “boxy” looking source mesh, and then have it magically become smooth just by clicking a button or adding a generator or attribute is really the bees knees.  Need more detail?  Add it to the source mesh gradually, checking your SubD mesh as you go. 

SubD modeling does have some characteristics to be concious of in order to get the best results.  First, note that the resulting SubD surface will be slightly smaller than your source mesh, effectively contained within the original mesh.  So, if you are modeling to blueprints, you will need to make adjustments on the source mesh in order to have the SubD mesh properly conform to the blueprint profiles. Next, SubD modeling prefers quadrilateral (4 sided) polygons on the source mesh.  You can get away with triangles, but its a good idea to hide them where they will not be seen by cameras at render time, as they can exhibit a “pinching” artifact.  N-sided polygons can work in some types of SubDs, but doing so will cede control of the resulting surface explicitly into the hands of the computer.  That is rarely a good idea, and even if your SubD method allows for n-sided polygons, most professional modelers avoid them as much as triangles.  Point of fact: it is extremely possible to have SubD source meshes contain only quads; it can take a bit of creativity or experience to achieve the result, but its worth it in the long run.  There are plenty of online forums and books that will describe this technique in detail.

SubD surfaces have become the preferred form of modeling for characters, as they offer tremendous benefits over any other method, and with few restrictions.  Perhaps the most troublesome aspect of SubDs is that they are completely arbitrary, and as a result, you are responsible for creating a good UV layout yourself.  You will get no assistance from the data, as you do with NURBs (in the form of inherent UV coordinates).  You will need to create, assign, and arrange the UVs on your mesh in order to paint image maps for your work.  Depending upon the complexity of the creation, creating UVs can get rather tricky…

 

Category:Glossary

Category:Modeling

Category:Rendering

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