subject: 3d models Lesson 15 - Onward and Upward - Part 1 [print this page] 3d models Lesson 15 - Onward and Upward - Part 1
We could actually perform such an extrusion of a 2-D and 3D Models circle polygon to create the very same cylinder, but using the primitive is easier. Let's make the radius of the cross-section .25 meters (250 mm). The diameter of the cross-section circle is therefore .5 meters (500 mm). Make sure you've thought this through before you go on.
We'll be working in wireframe views here because learning to visualize in wireframe is a critical skill, and one not easily mastered. Here is a wireframe view rendered from a camera placed directly in front of the cylinder
Huh?!
We'd better look at a shaded render of the very same scene to get oriented.
Stop and take a moment to understand these two images and how they correspond. The wireframe view is terribly confusing. The main problem is that the image is in true perspective. In perspective view, as our eyes or a camera sees in the real world, objects contract with distance.3D Models This is precisely how we judge the distance of an object, comparing its apparent size with our own judgment of its true size. Looking down railroad tracks, we see them appear to converge at a single point in the infinite distance. We know this is an illusion. This is the nature of perspective. Thus in our wireframe view of the cylinder, the back side of the cylinder appears smaller than the front side, and the faces on the side appear to converge toward the center. Even this interpretation can been very difficult to see, but try to recognize it in the image. The problem is (as with many visual tricks associated with the work of M.C. Escher) the mind's effort to make sense of conflicting interpretations, and its bouncing back and forth between them.
Notice, however, how perspective distortion helps us to understand the shape in the shaded view. The vertical ends appear to bulge out in the middle. Our mind interprets this to mean that the middle horizontal of the object is closer to us than the top or bottom horizontal edges. Without the bulge (and particularly without the shadowing), we would interpret the image as a flat rectangle rather than as a rounded surface bulging out toward us. The 3-D artist must become sensitive to all the clues that reinforce the illusion of objects occupying 3D Modelsspace.
If we rotate the cylinder around the vertical (y) axis, the true nature of the shape is more comprehensible, though the perspective wireframe is still confusing.
But, fortunately, there is another way of viewing wireframes.
