Attaching Entities to CAD Surfaces
FRED’s CAD import feature transfers geometry from STEP or IGES files in the form of parametric curves and surfaces. These curves and surfaces are based upon the NURBs representation common to all CAD software. During import, FRED makes no attempt to identify surface types and substitute native geometry. All CAD objects retain their original representation as NURBs. As a result, imported objects all share a common coordinate system; namely the Global Coordinate System. The fact that there are no local coordinate systems associated with CAD geometry undermines the ability to “attach” Analysis Surfaces or position other entities at the location of a CAD object. The purpose of the article is to provide a method for properly locating and orienting an entity with respect to CAD geometry.
The script UV_2_XYZ.frs which accompanies this article queries a CAD surface using the command ExplicitSurfEval. When run, the script prompts the user to specify the CAD surface to “attach to”and the entity to “attach” as shown in Figure 2. A second dialog (Figure 3) displays the UV coordinate limits and allows values to be entered. Selection of UV coordinates is largely trial-and-error, however, mid-range values are a good starting point. In this example, U=0.5 & V=0.5 conveniently locates the Analysis Surface at the center of the end cap as shown in Figure 4.
The functionality offered by this script greatly simplifies positioning and orienting entities with respect to imported CAD surfaces. At some point, this will become a permanent feature in FRED’s GUI.
Download the FRED Script: UV_2_XYZ3.frs