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MAA 1134: Principles of 3d Modeling Through critical analysis, the student will apply basic design principles to the solution of visual problems using elements of 3D design. The student will conceptualize 3D coordinate systems, construct 3D models, and perform mathematical computations as they apply to geometric construction.

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Extrusion modeling (sometimes refered to as edge modeling) is a technique which I find works best for individual artists who are tradditionaly more comfortable with the concept of contour drawing. We begin using the Create Polygons Tool (Polygons--> Create Polygons Tool). Using this tool we can draw out a silhoutte of the aircraft.

Next we shall select all of the edge on our silhoutte and extrude them in one direction along the X-axis to produce a strip of faces. Delete out the inside face and you are left with this:

Note that FOR EVERY "IN" THERE WILL BE AN "OUT". What this means is that if we draw 10 edges on the top of the silhoutte, we should also draw 10 on the bottom; 4 on the front, then 4 on the back as well. This ensures that we end up with enough faces to match so that we have an all quad mesh. The challnge of extrusion modeling is to maintain the same sort of grid flow that we achieve by default with box modeling, by calculating the "ins" and "outs" on our own. However, the benefit of this type of modeling is two fold. 1, it is extremely quick to set up several contours, merge them together, then extrude and append. 2, unlike box modeling where we have a mass of verticies which are initially created in the wrong place and must be moved to the correct position, we can create verticies in the correct place on the first try.

1. With the first silhoutte created from the side view, lets draw out a silhouttes for the front view representing areas at the cockpit, wing, and tail of the plane, using the in and out concept.
2. Again, extrude out the edges and delete the unnecessary faces.
   
3. Combine together the "strips" of polygon faces to make them all part of one object.
4. Use the Append polygon tool to fill gaps and connet the strip.
5. Use a combination of the Extrude Edge tool and the Split Polygon tool to add more faces.

In some cases you might notice that when appending together the different strips,

that the new face gets flipped inside out. To understand this, we must examine the concept of Surface Normals.

SURFACE NORMALS: or just normal, is a three-dimensional vector which is perpendicular to that surface. This vector line is what informs the renderer which was the object is facing (out or in). This determination is made by the right-hand rule, and is why we append in a counter clockwise fashion. It is important in determining which way textures bump when displacement, bump, or normal mapping. It is also important in determining the way dynamic simulations such as hair and fur work, since an inside-out face will grow hair INTO the body instead of out.

We can view the direction our normals face by going to Display-->Polygon Components-->Normals (or short normals). You should now see something like this:

If our normals look inside out on a section, we can reverse them using Edit Polyongs-->Normals-->Reverse with the appropriate faces selected.

Once they are reversed we can turn the annoying Normals display off (Display-->Polygon Components-->Normals) and the our append task should work appropirately.

We can also utilize our normals to make our object feel softer or harder. Edit Polyongs-->Normals-->Soften/Harden-->options box will allow us to alter our model in too look like the following: