Modeling with nurbs deel3

Editing Surfaces

The commands we use to edit nurbs-geometry are all found in the surfaces menu set, under the edit nurbs menu.

Attach surfaces

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Edit Nurbs > Attach surfaces: When we attach two surfaces, the Isoparms will have to be combined in one to generate the new attached surface. If the Isoparms don't line up they could be moved, possibly altering the curvature of the surface or extra isoparms are integrated. If the number of isoparms doesn't match new ones will be created to support both sets of the surfaces. The surface will move to close the gap between the two surfaces. If the isoparms are connected the curvature of the surfaces may alter due to the way the isoparms connect with each other. They can blend together or keep their curvature and make a hard connect without influencing the other isoparm.

attach without movement

Edit NURBS > Attach Without Moving blends surfaces together, but they don't move towards each other. The surfaces themselves will retain their shape, their will be a surface created to fill the gap and the surface will try to align its tangency with the existing surfaces.

align surfaces

Surfaces > align: With this option the surfaces are aligned. Just as the curves there are three methods of alignment. The C0 –positional alignment, the C1 – tangency alignment ( the surface will make a smooth connection with the least impact on its original shape) C2 – Curvature. The curvatures will be matched to generate a smooth transition. The in and out curvature will be the same, the effect on the existing surface will be larger. In the option box the settings of the alignment can be altered.

open/close surfaces

Surfaces > open/close surfaces: Just as a curve a surface can be closed. The function works like the attach option with the difference that the attached edges belong to the same object. A surface can be closed in both directions or one of the two directions.

detach surfaces

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See also the example video's at the bottom of this page

Surfaces > detach surfaces is used to split a surface using one or more isoparms as a cutting edge. The result is two or more separate surfaces. The advantage of this method is that the resulting geometry still will be defined by a set of crosswise isoparms and will have the full functionality of a NURBS surface, opposed to trimming, which effectively only hides specific parts of a surface.

project curve on surface

Surfaces > project curve on surface: To be able to trim a surface at least one curve (curve on surface) should be present that divides the surface in (at least) two parts. Maya has the option of projecting a curve on a surface. The curve will be projected along the axis of the view port or the normal of the surface. The result will be a curve on both sides of the surface.

intersect surfaces

Surface > Intersect creates a curve-on-surface along the intersection of two surfaces, which could later be used for trimming for instance.

More information and problem solving on the Intersect Surfaces command

trim tool

Surfaces > trim tool can be used to cut out or cut off a part of a surface. The cutting edges are closed curves on the surface or curves moving van one edge of the surface to another or the same edge of the surface. The surface within the curves can be deleted or kept and the surface outside the curves deleted.

When you've created a curve-on-surface with Intersect Surfaces or Project Curve on surface, the trim tool removes the parts divided by the curves.

To remove parts of your geometry that are intersecting:

Select the two surfaces that are intersecting, and need removing.

Go to Surfaces > Intersect, this will create a curve on the surface of both the objects, this curve can later be used for trimming (removing parts of the geometry).

Now the NURBS geometry is ready for trimming. To trim: Select the object to be trimmed, go to Surfaces -> Trim Tool And click on the parts of the geometry that you want to keep (a dot will appear on the parts that are preserved). When ready, press ENTER.

Repeat this process to make a hole in the other part of the geometry.

More information and problem solving on the trim tool

insert isoparm

Edit NURBS > Insert Isoparms: Just like curves it's possible to refine a surface by adding vertices. In the case of a surface we add isoparms which in their turn are defined by the vertices. Adding an isoparm will increase the vertices of the surface. If after generation of a surface, the surface locally has to be adjusted and more vertices are needed to support the transformation, inserting a new isoparm can be enough to enable the desired transformation.

extend surface

Edit NURBS > Extend Surfaces: Extends surfaces at one end or both. The distance can be specified in the Option Box. The direction ('U', 'V' or both) of the extension is also set there. These can also be altered afterward through the channelbox.

offset surface

Edit NURBS > Offset Surfaces: Offsetting a surface is a quick way of generating a closed volume (or 'thickness' as you will). The offset surface and the original can easily be closed by lofting the edges of the surfaces. Attaching the surfaces will generate a closed tube.

round tool

Surfaces > round tool: The round tool is used to generate beveled edges on surfaces. The tool has the advantage in contrast to the bevel option that a rectangular edge can be beveled without first adjusting the surfaces themselves.

circular fillet

Edit NURBS > Surface Fillet > Circular Fillet enables you to make smooth transitions between two intersecting surfaces. The fillet tries to accommodate a tangent continuity. The Radius of the fillet can be adjusted. If the radius is to big the fillet may possibly fail.

More information and problem solving on the Circular Fillet command

freeform fillet

Surface > Surface Fillet > freeform fillet: Free form fillet is basically the same function as the circular fillet. The difference is the way the fillet is defined. With a circular fillet, the fillet is created between two objects. With the free form fillet the edges of the fillet is defined by curves on surfaces. This will create the option to make very complex fillets, with the fillets still tangency aligned with the surfaces.

fillet blend tool

Surface > Surface Fillet > Fillet blend tool: The surface blend fillet is a good example how the topology of NURBS surfaces influence the possibilities to adjust a surface. With the Surface Blend Fillet tool it is possible to blend multiple surfaces together. By creating the surface the tangency will be aligned with all the surfaces where the blend is applied to. In the selection option of the tool, the first thing which is asked is to select the left edge and after that the right edge. This will mean that the direction of the blend surface is defined in one direction by the selection. Twisting of the surface will mean that the surface direction has to be altered. This can be done after the blend is made.

Examples of curve based modeling

Using the four methods of form generation based on Nurbs curves

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Use of curves from geometry to generate new geometry

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Common problems

Several problems can occur when modeling with NURBS. Modeling with nurbs: Troubleshooting describes common issues and the solutions.