# Visual Evaluation of 'Lines' - Curves, Edges and Isoparms

The most accurate and informative way of assessing the 'quality' of freeform curves is to visually analyse the 'curvature'.

The *Curvature* is the *Inverse of the Radius* at any one point.

It is the way in which the curvature changes along the curve - the *flow* - that informs us about the shape, and this is typically displayed as a series of lines known as a *comb plot* :

- The length of each curvature line is proportional to the inverse of the radius of the curve at that point.
- The direction of each curvature line is at 90 degrees (normal) to the curve at each point.
- The red outline shows the smoothness and character of the curve.

# Locators → Curve Curvature

Apply the Curve Curvature tool by clicking on a curve or edge. At this time (while the locator is active) you can adjust the comb plot interactively using the mouse buttons.

To go back to an existing comb plot to change the settings :

- Use Pick → Locator if it's not already active.
- Use Windows → Information → Information Window to change the settings.
- Use Delete → Locators to remove.

# Understanding the 'Flow' of the Curvature Comb

The comb plot can give you valuable information on the look and 'feel' of your surface, and with experience you will learn to interpret the comb plot and undersand how it relates to the real-life surface.

Here are some typical interpretations:

# Evaluating Continuity *Between* Curves

So far we've just looked at applying the comp plot to a single curve or edge. But comb plots are key to accurately understanding how two curves or surfaces join - their 'continuity'.

The four continuity levels, G1, G1, G2 and G3 are explained in detail in the Matching and Aligning Theory Builder.

This is how the comb plots between two curves are shown for each continuity level:

# Curvature Comb on Isoparms

A curvature comb plot can be applied along the isoparm directions of a surface using the Control Panel tools:

- Control Panel → Display → Curvature U/V (Displays curvature on the edges and isoparms of a surface).
- Control Panel → Curvature Controls the display of the comb plot - (size and spacing).

# Curvature Comb on Cross-Sections

Curvature comb plots can be applied along cross-sections using one of:

- Windows → Cross-Section Editor.
- The xsedit icon on the Control Panel.

This has the advantage that it is independent of the surface orientation and isoparm direction, so gives an accurate comparison across different surfaces.

It's important to note that these comb plots are applied to the tesselated surface, and so the accuracy is controlled by the Diagnostic Shading tolerance setting.

For more information on creating different types of cross-section, see the v2011 Update Movies - Cross-Section Editor.