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Intersections
For any artist trying to draw three-dimensional shapes,
intersections are an important factor in describing the forms. We
can see this best in nature where crystalline forms are involved.
There is one form, which if presented by itself in its entirety, has
no intersections. That’s a sphere, and it requires the shading
provided by light to define its surface.
In the real world, not the abstract one of descriptive geometry,
much more is at play than intersections. I’ve already alluded to
one, light; but there are more. As 3D modelers we need to
examine the things that make our renderings believable. I’m going
to take the idea of intersections to a more realistic level and refer
to that level as transitions.
Transitions
Transitions include intersections, but are more complex. They are
also needed in nearly all cases if we want to present something
realistically. Take a cube, for example. If the cube is all brown and
placed with one face resting on a horizontal plane that’s all green,
we can see that the cube is sitting on the plane or suspended
above the plane or coming up through the plane. We can’t
distinguish among the three unless we add light and shadow.
(Moreover, if the plane were tipped and the cube were suspended
above the plane, we would not know either condition.) Even adding
light, and assuming the plane is level, we can’t tell whether the
cube is sitting on the plane or coming up through it unless we
know that we’re dealing with a cube. Then we would know by the
proportions of the visible object.
Buildings. In real life, say a house sitting on the ground, we have
familiar clues that can help us determine the exact relationship of
the house and the ground. A house is generally built on top of a
foundation, and a bit of that foundation pokes up through the
ground to keep the wood framing of the house away from the
ground, where it is likely to wick up moisture. In America we are
also accustomed to surrounding our foundations with bushes,
though that would not be the case with a barn.
Something else happens besides light, shadow, and shading (notice
the side facing the sun is a lighter shade of its color than the side
not facing the sun). The ground around the house may be different
in the sense that it is more worn where people walk, and is
probably greener where the lawn is maintained than where the
lawn is allowed to become meadow. We may also notice that
variations occur in paving that surrounds a building, especially if
automobile traffic is involved.
Virtual Railroader - 6 - May – June 2005