How Do You Create 3D Geometry?


The process of creating 3D geometry can be quite difficult or tedious, depending on the shape or complexity of the object. Pilot3D gives you many tools to make this job easier for objects made up of smooth curves and surfaces. There are a number of ways to get started, but first you need to understand how NURB surfaces are pieced together to create 3D objects. NURB surfaces are rectangular-like grids of row and column curves that define a smooth, membrane-like surface. It can be stretched into any shape you like, but the more non-rectangular the shape, the more difficult it will be to shape and fair. Your job is to determine how to divide a 3D object into one or more rectangular surfaces. There can be many ways to do this, but some ways will be easier than others.


1.   Perhaps the easiest approach is to start by defining the key edges or control curves of the object using the curve (and polyline) entities. These control curves will define the boundaries between the various NURB surfaces used to construct the 3D shape. There are no limitations to these curves that will form a “wireframe” representation of the model. This will give you a good idea of the shape of the object, but it is not a complete 3D model. This is because you need to define every square inch of the model by skinning or covering it with NURB surfaces. Only then can you do exact 3D shaping of the object and be able to render or display the object accurately in 3D. Once the 3D control lines have been shaped, you can use various tools in Pilot3D to cover the object with surfaces. The skinning command will be the most powerful one for this in that it allows you to fit a NURB surface between any two or more curves. These curves can even be made up of trimmed edges of other surfaces.

2.   Another approach is to start from scratch with a simple, two row and two column surface. You can create this surface using the Surf-Add Surf command. Once created, you can position the 4 corner points of the surface where you expect them to belong. Then you can start adding in additional rows and columns, one-by-one, to the surface to add shape and control flexibility. As you add in each row and column, you can move the new edit control points to their proper positions. You should add only enough rows and columns to achieve the shape you need. To finish off the exact shape of the surface, you should first edit and fair the boundary edges of the surface. Once those are set, then you can then perform the final shaping and fairing of the internal surface edit points.

3.   A third approach is to start with one of the generic 3D solid shapes: triangle solid, box solid, wedge solid, cylindrical solid, cone solid, or ellipsoid solid. These shapes can be solid or hollow, consisting of a user-defined thickness. The cylinder, cone, spherical, or ellipsoid shapes can also be full 360 degree revolutions or any user-defined range of angles. The shapes that are created are true 3D, bonded and editable solids. All edges are bonded with geometric relationships so that you can move any edit point without worrying that the solid will split apart. If your 3D model or part is close to the shape of any of these standard 3D shapes, then it may be easier to generate the solid and modify its shape rather than to create the shape from scratch.

4.   Of course, you can create 3D objects using any combination of the techniques listed above. Also, remember that you are not required to create or maintain a closed 3D solid model at any time. However, if you want to transfer the model to a true, 3D solid modeling program, then you will have to make sure that your model is close and has no gaps. This can be more difficult than it seems, but there are many industry tools now available that can help with this process.