184 ◾ 3D Animation for the Raw Beginner Using Maya
Before we look at this, remember that we can and do work with polygon surfaces that are
not completely enclosed in 3-space. And we work with completely enclosed basic shapes in
NURBS modeling. So, there is no sharp divide between straight- and curved-line model-
ing that says that polygon modeling is used only with enclosed surfaces like cubes and that
NURBS modeling is only used on objects that are not completely enclosed.
Isoparms
In Figure5.51, we have a NURBS plane. In Figure5.52, we have three NURBS planes: two
that are horizontal and one that is vertical. e horizontal surfaces are two stairs and they
FIGURE 5.48 A cactus
with badly scaled texture. FIGURE 5.49 Repeat UV values.
FIGURE 5.50 Cactus rerender. FIGURE 5.51 A NURBS step.
Materials, Bump Maps, Lights, Projection versus Normal Textures ◾ 185
need to be connected via the vertical plane. We want to make the connection smoothly
curved, as this is carpet we are modeling, not metal or wood. In Figure5.53, we have
selected the top plane and right clicked, and then chosen Isoparm mode. Notice that we are
not selecting Edge mode like we might in polygon modeling, although for many purposes,
NURBS isoparms can be treated like polygon edges.
Let’s go over the dierence between a curved line and an isoparm. In particular an
isoparm is a more narrowly dened geometric concept. An isoparm is a line across a
NURBS surface where the u or v value
in 2-space is constant. us, the hori-
zontal hoops in a NURBS sphere are
isoparms, but in the vertical direc-
tion we single out half-hoops that go
from top to bottom as isoparms. (You
have to look at the surface without
considering its orientation in 3-space,
because u, v values are local to a given
surface.)
In a sense, an isoparm creates a
NURBS cross-section. Try creating
a NURBS sphere primitive with the
Create menu. Go into isoparm mode
and click on some of the curved lines.
You will discover that only the curved
lines that have a constant value for u or
v are actually isoparms. At rst glance,
FIGURE 5.52 Two steps.
FIGURE 5.53 Isoparm mode.
186 ◾ 3D Animation for the Raw Beginner Using Maya
this seems to not be true, however, as there are fully connected curves that wrap entirely
around the sphere from top to bottom, but they are actually made up of two isoparms.
Why don’t two of these curves form an isoparm? e answer lies in the following:
When we are manipulating the sweep of a NURBS sphere, the two parts of one of those
loops that look like they should be isoparms do not remain in the same plane. And
they have neither a constant u value nor a constant v value. is is because a seemingly
enclosed NURBS primitive (sphere, cylinder, etc.) can be opened up, and which axis
is used to unfold the primitive controls which curves are isoparms. A default NURBS
sphere in Maya, for instance, has a sweep that opens the sphere from top to bottom. is
causes horizontal hoops on a sphere to be isoparms, but only half-hoops are isoparms in
the vertical direction.
Connecting Stairs
In Figure5.54, we have selected two isoparms: one from a vertical face and one from a hor-
izontal face. e bottom face is tucked just a bit under the horizontal face; this is because
we want to model the way carpet rolls back up under a stair. We then select:
Surfaces Main Window → Edit NURBS → Stitch → Stitch Edges Tool
We see this in Figure5.55. e result is seen in Figure5.56. Maya has connected the two
NURBS surfaces by creating a smooth curved surface between them. e geometry of the
connecting surface can be tailored with the settings of the tool.
Putting a Material on the Stairs
To carpet our stairs, we rst create a le as a projection texture and use a photo of carpet
as the texture image. In Figures5.57 through 5.59, we use interactive planar placement
to put a carpet texture on the stairs. is is done by projecting the carpet texture three
times: one on the vertical plane between the two stairs and once on each of two hori-
zontal planes that make up the two steps. We select the plane we want to texture, then
go into the Hypershade and right click on the
texture, and then choose Assign Texture’s
Material to Selection. e rendered result
is shown in Figure 5.60. ere is a hidden
imperfection there; the carpet texture under-
neath the lip of the stair is stretched.
Using the Append to Polygon Tool
for Connecting Two Stairs
We have connected two carpeted stairs and
have created a horizontal oset for each under
the top step, so that the carpet will tuck under
the lip of each step. We used NURBS tools to
do this. Here we take a quick look at doing a
similar thing with polygon modeling.
FIGURE 5.54 Two isoparms selected.
Materials, Bump Maps, Lights, Projection versus Normal Textures ◾ 187
First, we create the two planes needed for two steps. Importantly, we must use the
Combine tool and create one object out of the two. is tool is found by choosing:
Polygons Main Menu → Mesh → Combine (see Figure5.61)
e planes are not connected yet, but they are one object. Now, we select:
Polygons Main Menu → Edit Mesh → Append to Polygon Tool (see Figure5.62)
en we select the two edges of the two polygons that are closest together (see Figure5.63).
We hit Enter, and the two planes are connected by an angled polygon, creating the oset
of the carpet from the front of one step to the top of the other. e result is shown in
Figure5.64.
USING A FILE TEXTURE AS
A MATERIAL’S COLOR AND
MAKING A MATERIAL STICK
We are going to look at another creative
way to make use of a texture: substituting
it for the color attribute of a material. We
will also look at one way to prevent a tex-
ture from wandering once it is applied to an
object.
FIGURE 5.55 Stitch tool.
FIGURE 5.56 Stitch result.
188 ◾ 3D Animation for the Raw Beginner Using Maya
A Texture as a Color of a Material
e color attribute of a material can be
manipulated by assigning a le texture to it,
and then leveraging other attributes of the
material to create a combined eect.
Assigning an Image to a
Material’s Color Attribute
In Figure 5.65, we have created a Blinn
material and have clicked on the checker-
board icon to the right of its Color attribute.
We have then chosen File when the Create
Render Node panel has popped up.
FIGURE 5.57 Texture placement.
FIGURE 5.58 Texture rotated.
FIGURE 5.59 Two placements.
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