曲面模型建構

Curve/surface analysis - Visualize and analyze curvature on a sketch in the Part Studio. Access the Curve/surface analysis dialog by clicking Shift+c, right-clicking on a sketch, part, or surface, or clicking the Show analysis tools icon () at the interface's bottom right corner.

These tools show curvature combs (the intensity of the curvature at a certain point along an edge or face), and control point grids. Ideally, the curvature combs should have steady increases or decreases.

The following example looks good without evaluation tools but shows extreme fluctuations in curvature (especially in the red U direction below left) when Curvature/surface analysis is enabled. The outer edge is especially problematic (below right):

Additionally, the control point grid is a measure of the complexity of the surface. The flow and density of control points can illustrate a model with too many control points:

Connection analysis - Assess or report the connection between curves and surfaces in a Part Studio or Sketch. Access the Connection analysis dialog from the Show analysis tools icon () at the bottom right corner of the interface. Select curves or surfaces to analyze; the dialog box (shown below) populates with results automatically upon selection, along with color coordinated indicators in the graphics area.

Zebra stripes and Color map - Zebra stripes represent the reflection of a striped room on the current model, faces, or surfaces in a Part Studio or Assembly. This allows you to see whether or not the curvature across edges and faces are aligned and continuous. Access Zebra stripes from the Show analysis tools icon () at the bottom right corner of the interface.

Zebra stripes do not match up with G0 or positional continuity. In G1 or tangency continuity, they match up directly on the edge but diverge sharply. In G2 or curvature continuity, the zebra stripes pass smoothly through the edge (shown below left). Zebra stripes also allow you to see defects or imperfections in the surface (shown below right):

Curvature color map - Enables deeper investigation of curvature by applying a gradient of color of your choosing onto a face or surface in a Part Studio. Adjust the scale of the color gradient and choose from different types of color maps to gain the best visual representation to discern surface continuity and transition between edges.

The most common color map curvature option is Gaussian, which is helpful in determining if there are local imperfections or drastic changes in surface curvature. The rippling detected in the above Zebra stripes image is more apparent viewed with Gaussian curvature:

Dihedral analysis - Access Dihedral analysis by selecting the Show Analysis tools icon () at the bottom right corner of the interface. This displays the angle between the normals of 2 surfaces at a shared edge. If the angle is zero, the 2 surfaces are at least tangent at that location along the edge. In the example below, the dihedral intentionally changes from a hard crease to a smooth tangent blend at the other end of the curve:

Deviation analysis - Display the minimum and maximum deviation between 2 curve chains in a Sketch or Part Studio, or 2 surfaces in a Part Studio.

Example showing the Max/Min deviation between two curves

Example showing the Max/Min deviation between a "Source" surface and a surface "To measure"

See Deviation analysis for more information.

Reflection analysis - Renders the model in the graphics area with a reflective material and environment image of your preference.

See Reflection analysis for more information.

Highlight boundary edges - Highlight any open edges in red. Access Highlight boundary edges from the Camera and render options dropdown () below the View cube. This is useful when you are trying to identify any open areas in a surface to form a solid.

Face Tangent Angle - Face Tangent Angle (a Measure tool) provides quick feedback on whether a curve approaching a face is tangent at its endpoint. Select the face. The tangency angle is displayed to the left of the measure tool. This is useful to test continuity before completing a Loft or Boundary surface:

View in high quality - Turns on the highest available quality tessellation for the view and is essential to identify curve imperfections and evaluate continuity accurately. Access View in high quality from the Camera and render options dropdown () below the View cube.

Shaded with edges/Tangent edges - Useful to view edge continuity more clearly. Access both these options from the Camera and render options dropdown () below the View cube.

Boundary surface - Some features provide little control over the curves to create a surface, over-complicating and decreasing surface quality. A Boundary surface provides complete control over the U and V direction curves. The resultant surface is only as complicated as the input curves. Loft, Sweep, and Fill features create curves in one or both directions that cannot be controlled, complicating the surface.

For example, the same surface is built with a Boundary surface and a Sweep. The sweep develops curves along the V direction along the path, creating an overly complex surface:

The same surface is built with a Boundary surface and a Loft. The Loft creates a dense control point grid in both directions:

Fill - Fill patches small holes in a surface. After using Fill, evaluate the resultant surface to ensure a quality surface. In the example below, Fill adds a ripple towards the bottom. Loft creates a better control point grid with no rippling, but the Boundary surface creates the smoothest, most consistent result:

Face Blend and Fillet - Face blend and Fillet create complex edges similar to projections or split operations. Edges created by Face blend or Fillet have a higher chance of failing and introducing imperfections due to the complexity of these features. Since this is usually cosmetic, building the surfaces to the virtual sharps and adding these features at the end is best:

Use Beziers instead of Splines - Splines have points defined along the curve and handles on the start and end points. Beziers have control points defined along the control polygon offset from the curve. Bezier curves increases and decreases smoothly with no continuity breaks:

Keep curves simple - Use the Bezier tool and start with 3 or 4 control points (including endpoints). Add the least possible amount of Spline points.

• The degree of a Bezier is the number of control points minus 1. Beziers should generally be of the degree 3, 5, or 7. Limiting the degree of a single Bezier curve to 7 is best because the mathematical computation becomes very complex at higher degrees. Moving one control point affects the entire curve, and higher-degree curves are difficult to adjust without introducing imperfections.

• Use a consistent flow of control points to ensure smooth curvature changes with no unintended intensity changes.

  Below are a few examples of curves with poorly placed control points. The first has a zig-zag between the first and second points (outlined by the circle). The second has control points positioned above and below the curve. It is only appropriate to change which side you place control points on when you intend to add inflection to the curve. The third does not have smooth spacing between control points. The point’s spacing compared with the others is drastically different (indicated by the arrow below):

  

Avoid building from trimmed edges or projected curves - Since these are made from trimming operations or projections with many spans (segments knotted together) of degree-3 (cubic) splines, anything built from them is more complex and imperfect.

For example, the surface here has a denser control point grid when creating a ruled surface directly from a trimmed surface's edge (below left). Instead, overbuild both surfaces and use a Mutual trim to trim the excess at the intersection (below right):

Instead of projected curves, see if Bridging curves can build the same geometry with less complexity. Bridging curves are Bezier curves that reach up to degree-5, depending on end conditions.

Aim to use four-sided surfaces - Four-sided surfaces have the most consistent control point grid. Creating a surface without four sides leads to singularities (degenerates) or irregularly spaced control points (shown below left). Overbuild and trim the surface with a reference surface using the Split feature. This creates surfaces with different edge profiles, while maintaining a consistent control point grid (shown below right):

Use symmetry when possible - Apply constraints for continuity to ensure a smooth transition across the centerline.

• Use reference lines in a sketch with Tangent or Curvature constraints.

• In a 3D model, add reference surfaces to assist with the continuity of the generated surface.

Use shortcut menus and hotkeys - Use shift+c (Curve/surface analysis), shift+d (Dihedral analysis), and shift+r (View in high quality). You can also customize the Shortcut toolbar (s) under My account > Preferences > Shortcut toolbars.