SolidWorks 2011 Parts Bible - Matt Lombard [303]
Whether or not the data you receive is of value to you depends in part on what you want to do with it. If your data only has to be a visual representation, and not a CAD-accurate NURBS (Non Uniform Rational B Spline) model, you may be able to accept a wider range of data types. If you are looking for manufacturing quality data, some formats are simply not worth your time to deal with. These file types are mesh data that SolidWorks can read and are useful for visual data, but useless for clean NURBS data:
• *.stl. Stereolithography, typically used for rapid prototypes
• *.vrml. Virtual reality markup language, typically used for games, an old format that allowed color to be transmitted with the mesh geometry
• *.cgr. Catia graphics
Converting point cloud data
One of the most common import questions is how to import data from file formats such as *.obj or *.3ds, among others. These file types are mesh files, which means they are simply point cloud data. SolidWorks and most other CAD programs create geometry that is based on NURBS data, where the surfaces are represented by very accurate mathematics. Mesh data is represented by points in space, which is much faster to work with because it is similar to the data used by graphics cards and drivers to display curvy shapes. Mesh data is used by Hollywood, video game developers, and computer graphics studios, and NURBS data is used in engineering and manufacturing. It is easy to convert NURBS to mesh, but more difficult to convert mesh to NURBS. The mesh to NURBS conversion can be done, but complex software and specialized expertise is needed for it to happen correctly.
Note
SolidWorks can make the mesh to NURBS conversion with the Scan To 3D software that is part of the Premium package. Because this is not included in the Standard package, it is beyond the scope of this book and will not be covered here.
Understanding the IFC file format
The *.ifc (Industry Foundation Classes) file format is from the AEC (Architecture, Engineering, and Construction) industry, which means it is for buildings. IFC is related to the BIM (Building Information Modeling) initiative that enables the transfer of more than just geometrical information about a building. Much of the AEC discussion is well beyond the scope of this book. If you want more information on IFC, BIM, and AEC modeling, a good place to start is at www.aecbytes.com/feature/2004/IFCmodel.html.
SolidWorks appears to be reaching into this market with a couple of enhancements in the 2011 release, including the large-scale design options with 3D sketches and weldments.
Understanding the Traditional Role of Direct Edit Tools
What I call “direct editing” is also known by other names. You may hear it referred to as direct modeling, explicit modeling, history-free modeling, or even synchronous technology. I call it direct editing because the way the geometry is created is all approximately the same and the difference is in the way edits are made. In fact, one of the claims to fame of direct editing software tools is that it is the only system that deals effectively with imported geometry, because “geometry is geometry,” regardless of its source — native or imported. This is the reason why I cover imported geometry and direct edit tools together in this chapter.
Traditionally, direct editing CAD software has lived by the rule that how you create geometry should not affect how you edit the geometry. Therefore, direct edit CAD packages still use functions like extrude and revolve to build parts, but they would not return to those functions to edit the part; they would instead directly manipulate faces of the part by moving, offsetting, and rotating.
CAD software that depends on direct editing tools has existed for a long time: it has been around longer than history-based CAD software. In the last several years, some new direct edit CAD products (Sketchup and Spaceclaim) have appeared on the scene and have renewed an interest in direct edit techniques. Until this recent