Modeling with nurbs deel2
Contents
Introduction
When working with nurbs you need the modeling menu set:
In the edit curves menu you can find all commands with which you can alter curves. The surfaces menu contains all commands which create nurbs surfaces and in the edit nurbs menu you will find all commands to edit nurbs geometry.
Construction history
In Maya geometry has a history. This history describes what has happend to that geometry, and how it was made. This information can be used to your advantage, because you can change things (for example values) afterwards. Which results in a more interactive way of modelling. For example; if you make an object based on curves, and change these curves, your object will also change (see image below).
History can be recognized in several ways. The most obvious is in the channelbox on the right side of your screen. This contains the regular X, Y, and Z transformation values, but also inputs and sometimes outputs. If there is information in the in- or outputs box, there is history. You will see outputs if your selected piece of geometry is used to make another piece of geometry.
Also history is recognizable if you select an object, and the output geometry becomes purple (in wireframe mode).
In order to change an object with the use of history, you can do several things:
- Change the object(s) that were used to make the with history connected object (as done in the above example).
- Change the value in the channelbox numerically, by clicking on an out- or input connection.
- Use the manipulator tool to change the value graphically (as done in below example).
- Deleting history
History is often very handy, and it is recommended to keep it as long as possible. But sometimes it gives unwanted results. For example, when you select some objects and move them, some objects move twice as fast. This is related to the history of these objects, where it accumulates the movement.
If you want to prevent this from happening, you can either select only the output geometry, and not the objects that were used to create the output geometry (like the curves in the above vase example), or delete the history. Which can be found in EDIT - DELETE BY TYPE - HISTORY.
Once the history is deleted, you cannot get it back. The geometry becomes dumb, and is no longer linked to other objects, and you will no longer be able to take advantage of the link between objects.
selection masks
A key to understanding maya is understanding the way maya builds the geometry. For example: A polygon exists of Vertices and Edges. Editting the components of a polygon edits shape of an object, and the form or location of the other components. In order to change the shape on an object in maya, you can also modify component-type information to alter the shape.
There are a variety of component types, such as points, isoparms, faces, hull, pivot points and handles. These components can be used to interactively modify and reshape the appearance of an object. These may be confusing, but is very usefull to understand the different type of components, and the role they play in creating objects.
When you work with NURBS you almost immediately work with curves, often these curves are on the same place of the edge-isoparms of surfaces. Thus it often occurs that you want to select a curve, and by accident select a surface. In order to prevent this, you use selection masks. First you make sure you are in object mode. Than disable either sufaces or curves, by disabling one, you prevent selecting that type by accident.
- Surface selection:
Disable this option if you want to prevent selecting surfaces by accident.
- Curve selection:
Disable this option if you want to prevent selecting curves by accident.
When wanting to change NURBS or NURBS curves, you can use the component mode, in which you can select parts of a curve or geometry.
- Control point selection:
Use control points to change the shape of the surface or curve.
- Edit points:
Use edit points to select points on a surface, to add knots or change the surface or curve.
- Isoparms:
Use isoparms to extract curves from, or the creation of geometry
- Hulls:
Use hulls to select a line or row of cv's.
Creating surfaces
The commands we use to create surfaces are all found in the surfaces menu set, under the menu surfaces.
loft
Surfaces > loft creates a surface between two or more curves. It creates a surface from curve to curve in order of the selected curves.
More information and problem solving on the loft command.
extrude
The extrude option is used to create NURBS geometry. One setting in the tool is used to extrude a single curve in a certain specified direction, creating a surface. This extrude option in one direction uses only one curve.
Extrusion along a path has the advantage that the direction of the extrusion can be controlled. There is however a disadvantage of generating a surface like this. The profile ( section ) of the surface generated isn’t constant if the curve along which it is extruded curves to much. To generate this geometry select all the settings on the right of the option box of the command.
First select the circle you want to extrude, then select the curve. And as final step select Extrude.
More information and problem solving on the Extrude command.
planar
Surfaces > planar creates a planar (flat) surface enclosed by one or more curves, isoparms or trim edges. Two conditions have to be met in order to create a planar surface successfully:
- the lines need to connect or intersect (no gaps between them)
- the lines need to be planar (flat).
more information and problem solving on the planar command
revolve
Surfaces > Revolve creates a surface by rotating a profile curve around an axis. The axis runs through the Pivot Point of the profile curve.
More information and troubleshooting on the Revolve command
bevel
With the bevel option you can make a beveled surface from a profile curve. Select a curve and then use the bevel option. This will create an extruded surface with beveled edges for a smooth transition.
square
The square option looks a lot like the boundary option however it is limited to four intersecting or connecting curves. First select the 4 overlapping curves, then use the square option to make a NURBS shape.
boundary
The boundary option will create a surface between an minimum of 3 curves connected to or intersecting each other. First select the three curves and use the boundary option to create the surface.
birail
The other method to generate NURBS geometry is to define the geometry in both directions with curves and then using the birail option.
