Page 159 - DCAP504_Computer Graphics

Computer Graphics

Oblique Projections
Oblique projection projects an image by intersecting the parallel rays from the three-dimensional source
object with the drawing surface. In oblique projection, the parallel lines of the source object produce
parallel lines in the projected image. The projectors produce the projected image by intersecting the
projection plane at an oblique angle.

Figure 10.13 Oblique Projection

As shown in figure 10.13, oblique projection is not really a 3-D system, it is a 2-D view of an object with
forced depth. One way to draw using an oblique view is to draw one side of the object in two-
dimensions that is flat. Then, draw the other sides at an angle of 45 degrees. Instead of drawing the
sides full size they are only drawn with half the depth creating forced depth - adding an element of
realism to the object. Even with this forced depth, oblique drawings look very unconvincing to the eye.
For this reason, oblique projection is not often used by professional designers and engineers.
10.3 Summary
• The line clipping is modified to clip the polygon. The clipping polygon is of two types: concave
polygon and convex polygon.
• The Sutherland-Hodgeman polygon clipping algorithm applies divide-and-conquer strategy to
clip a polygon.

• Weiler-Atherton Algorithm illustrates both the subject polygon and the clip polygon with the help
of list of vertices.
• The projection maps a point to its image on the display surface. The two basic method of
projection are perspective projection and parallel projection.
10.4 Keywords
Anomaly: The deviation from the general order, type or rule.
Isometric: This is the act of presenting equality in dimension and measurements.
Orthographic: In mathematical terms, this means perpendicular.
Polygon: A polygon is a closed, geometric, two dimensional plane figure formed by straight lines.

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