NURBS Modeling
January 24, 2003
By Brian J. Immel
Surfaces Menu
Revolve
As the name suggests, Revolve function takes a curves and creates a surface based on revolving the curve from the pivot center. This function is very good for creating things like vases, bottles and objects of that nature.
- Select a curve and hit Surfaces > Revolve option box.
- Play with the Axis Present option to create revolved surfaces
Loft
A loft is a surface created between two or more curves. A small tip about building NURBS curves from curves: If the curve at the beginning has four divisions, the curve at the end should have four divisions also. If the curves aren’t equal in divisions, Maya will try to make the surface anyway but it doesn’t know exactly what to do with the extra divisions and create a surface that’s a little less pretty and predicted.
- Select the curves.
- > Hit Surfaces > Loft. Maya will create a non-coplanar surface between the curves. What I mean by non-coplanar surface is that the surface created is not flat. The next function works only if the surfaces are coplanar.
Planar
- Create two or more curves that create a closed line or hit Create > NURBS Primitives > Circle. In order for this function to work, the curves must their ends touching one another making a closed loop.
- Hit Surfaces > Planar. Maya creates a planar trimmed surface. Trimmed NURBS surfaces are difficult to manipulate later on in the scheme of modeling and animation.
Extrude
Extrude can extrude a surface a pre-defined distance.
It can also create a tube to follow along a path.
- Create a snaking curve.
- Create a circle (Create > NURBS Primitives > Circle).
- Select the circle first then the snaking curve and hit Surfaces > Extrude option box. Change Style to Tube, Result Position to At Path and Orientation to Profile Normal. You may need to rotate the circle so that it sits at a right angle to the beginning of the snaking curve.
Birails
Selection methods works according a rider and rail(s) relationship.
Its important that the rider curve is tangent (touching) the beginning of the rail curves. If the rider curve isn’t touching, the birail function will not work. Also, there is not need to shift-select. The Birail tool already knows how many selections it needs to make before completing the function. The only exception is the Birail 3+ tool in which case, you must select the riders, hit enter, then select the two rails.
Birails work best if the rails have the same amount of EPs and the riders (if more than one) have the same number of EPs also.
Birail 1
- Build three NURBS curves. Two curves should be parallel to each other on the X or Z axis (the rails. The other curve will be our rider. Model the rider curve on the Y and Z axis.
- Hit the Birail 1 tool (Surfaces > Birail > Birail 1 tool).
- Select the rider curve first.
- Select the two rail curves. A NURBS surface will be created according to how the curves are laid out.
Birail 2
- Build four NURBS curves. Two curves should be parallel to each to each other on the X and Z axis (the rails). The other two curves will be our riders. Model the rider curves on the Y and Z axis.
- Hit the Birail 2 tool (Surfaces > Birail > Birail 2 Tool).
- Select the rider curves first.
- Select the rail curves next. Upon selecting the last curve, a surface will be created according to how you laid out the curves.
Birail 3+
- Build two rail curves on the X and Z axis.
- Build three or more rider curves and the Y and Z axis.
- Hit the Birail 3+ tool (Surfaces > Birail > Birail 3+ Tool).
- Select all the rider curves first. After you’ve select all the rider curves, hit enter.
- Select the rail curves. Maya will create a NURBS surface that looks a little like a hill with varying heights depending on the rider curves you made.
Boundary
Boundary tool can be used to create geometry to ‘fill’ holes created by trim edges or to create surfaces a loft cannot. Below are instructions to fill a hole left from a trim edge.
- Select the trim and duplicate the curve (Edit Curves > Duplicate Surface Curve).
- Select three to four EPs on the curve we just created and hit Edit Curves > Detach Curves. A boundary cannot be created from one or two curves; it needs at least three curves.
- Select all the curves and hit Surfaces > Boundary. This will create a surface that fits the trim we are trying to fill but it may appear to have a seam with the trim edge surface and boundary surface (another problem with trim edges).
Square
Square function allows you make a selection on a surface and make a copy of that selection.
- Select 3-4 isoparms on a NURBS surface. The first and second selection of the isoparms must intersect, second and third must intersect and the third and fourth must also intersect. Basically, you are defining an area to duplicate from.
- Go to Surfaces > Square. This will create another NURBS surface based on the selection you made from above. This comes in handy when you want to hand rebuild a surface.
Bevel
Does as it names says but its not very handy. The bevel it creates is separate from the geometry you’re working with and you then have to go through the hassle of connecting properly.
- Select the isoparm where you want the bevel to be on a surface and hit Surfaces > Bevel.
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