Creo Elements/Direct Modeling provides a utility to help you detect surface imperfections in parts and faces. You can analyze curvature values, check maximum and minimum radius values on surfaces, and check transitions between faces.
Curvature values on a face
The Surface Analysis utility calculates Gaussian or mean curvature values and displays the analysis graphically on the selected faces or parts. Color-coding, which you can adjust, indicates the positions of possible trouble areas. You can let Creo Elements/Direct Modeling determine the maximum curvature value to be analyzed, or you can specify a maximum manually.
The basis for an analysis is the facet model of a face or part. In general, the standard Creo Elements/Direct Modeling faceting is sufficient to give an informative analysis on bad surfaces. However, a finer facet model can lead to more accurate visual results. You can refine the facet model temporarily during a surface analysis to help you visualize the results more accurately. (Under 3D Geometry, click the Wire check box in the “Show Properties of ‘vport’” window to see the facet model of a part or face.)
Analyzing surface quality is particularly useful in detecting surface wiggling, which is the transition on a surface from convexity to concavity. This change is implied by negative Gaussian curvature, whereas convex and concave surfaces themselves imply positive Gaussian curvature. Surface wiggling is usually avoided in plastic housing design.
The figure shows an example of a part with a poor surface and the same part with an improved surface.
The part on the left demonstrates a surface with bad curvature behavior (rapid changes in color-coding). The part on the right shows a surface with good curvature behavior (smooth changes in color-coding).
Creo Elements/Direct Modeling uses a color distribution (for example, Green-Red-Blue) to display the analysis result. The most positive curvature values are displayed in the first color (Green), the middle color (Red) represents values close to 0, and the last color (Blue) represents negative values. All values smaller than the negative limit or greater than the positive limit are displayed with the most intense color values. Between the limits the color values are interpolated with respect to the current curvature value.
Maximum and minimum radius values on a face
Another feature of the Surface Analysis utility is the capability of checking maximum and minimum radius values of a face. As soon as you select a single face to analyze, graphical feedback indicates the main curvature circles (where the maximum and minimum radius values are found) on the face at the cursor point. Also, the maximum and minimum radius values (at the cursor point) are displayed in the prompt text line.
This utility is especially useful before shelling a part or thickening or offsetting a face part. The maximum and minimum radius data can be interpreted as follows.
When you shell a part, a positive offset value means an offset to the inside and a negative value means offsetting to the outside. You can analyze the radius values of a face of the solid that you want to shell:
• To shell a part to the inside (that is, by using a positive Shell offset value), you need only consider the maximum radius value. If this radius value is positive and smaller than the required shelling distance, then shelling fails because the offset surface cannot be generated without self-intersections.
• To shell a part to the outside (that is, by using a negative Shell offset value), you need only consider the minimum radius value. If this radius value is negative and larger than the required shelling distance, then shelling fails because the offset surface cannot be generated without self-intersections.
For the Offset and Thicken commands, a positive offset value means offsetting in the direction of the positive face normal and a negative offset value means offsetting in the direction of the negative face normal. Analyzing the radius values of a face in these cases would be done as follows:
• To thicken or offset with a positive offset value, if the maximum radius is negative and its absolute value is smaller than the offset value, then the action fails due to self-intersections in the offset surface.
• To thicken or offset with a negative offset value, if the minimum radius is positive and its absolute value is larger than the offset value, then the action fails due to self-intersections in the offset surface.
Transition between faces
In commands that create or modify b-spline surfaces, use the Zebra stripes analysis to calculate transitions between faces. When possible, the system analyzes the neighboring faces in order to support the face/face transition analysis.
Zebra stripes are a reflection of an imaginary striped sphere or cube. Watch the stripes at the transition edge. If the stripes do not fit together, this indicates that the transition between the two faces is not smooth. If the stripes do fit together and have a clear angle this indicates that it is a tangential transition. If the stripes fit together at no angle there is a near curvature continuous transition. Because the Zebra stripes are an optical analysis, a curvature continuous transition is not certain and must be considered "near."
