CATIA V5

Wireframe and Surface Analysis Techniques

This is the first article in a series discussing the tools available within CATIA to analyze the quality

of surfaces and curves. This article will focus on analyzing the quality of the wireframe.

Any surface designer will tell you that a surface is only as good as the wireframe it is created

from. A quality surface can only be created from quality curves. If we start with low quality curves, we will always get a low quality surface. As a result, the importance of analyzing curve

quality cannot be overlooked and should be a necessary step in the design process.

Before we can start analyzing a curve, we need to understand what differentiates a good curve

from a bad curve. The first thing to analyze is the continuity of the curve. There are three types of continuity - point, tangent, and curvature, with point continuity being the lowest quality and

curvature continuity being the best quality.

Point continuity occurs when the two curves share a common endpoint.

Tangent continuity occurs when the two curves share a common endpoint and are tangent to

one another at that point. Tangent continuity is acceptable for most surfacing applications, with the exception of Class A surfacing. For tangency continuity, the angle can measure either 0° or

180°.

Finally, Curvature continuity occurs when the two curves share a common endpoint, are tangent

at that point, and have the same radius of curvature at that point. Two circles joined together is a classic example of a curvature discontinuity. If you approach the endpoint from the left, the

radius is 40mm, but from the right it is 75mm (see Fig. 3). For curvature continuity, the radius should be the same from both sides.

The first tool that we will take a look at is the curve connect checker. This tool will quickly and

easily identify any continuity problems within a single curve or within a network of curves. Simply select the type of continuity to check for, set a tolerance range, and then select the curve or

curves to analyze. CATIA will then determine the trouble spots, if any. In the example below (Fig.

4), we are looking for tangency discontinuities that have a deviation greater than .5°. CATIA then highlights the problem areas and displays the tangency values. Be careful to interpret the data

correctly. At first glance it may appear that there are two tangency problems. However, upon further inspection, you will notice one of the problem areas measures 180°, which is actually a

tangent continuous situation.

Once you have identified the type of continuity in your curves, the next step is to look at the quality of the curve. Just because a curve is curvature continuous, that does not necessarily

mean that the curve is of high quality. To verify this information, we will use the Curvature Analysis Tool. This tool is used to detect curve imperfections that the naked eye may not see. It

performs a porcupine analysis on the curve. The spikes are displayed normal to the surface. The

magnitude of the spikes is based on the value of the curvature at each point and the direction is based on the curvature direction at that point. An inflection point occurs every time the curvature

changes direction (a bump in the curve). Sometimes a curve should have multiple inflection

points, but many times this is a signal that the curve is of poor quality.

Now that we know what we are looking for, let’s look at an example. In Fig. 6 there are two very similar looking curves, both of which appear two have three inflection points. However, by using

the curvature analysis tool, it becomes quite obvious that the bottom curve has some major flaws

in it.

The magnitude of the spikes on the curve reveals important information about the curve. When the magnitude of the spikes is small, this indicates a flat region on the curve. When the

magnitude of the spikes is large, this indicates a more rounded area on the curve. When transitioning between areas with different curvature, you want your transition area to be as

smooth as possible. Try to avoid sudden peaks and valleys in the graph; this usually indicates a poor transition area

Conclusion:

A high quality surface requires high quality curves. Rather than relying solely on the naked eye to

verify the quality of a curve or surface, use the tools available in CATIA. CATIA has a vast array of tools to verify and analyze the quality of curves and surfaces. These tools are very easy to use

and can be applied to a curve in seconds. First check the continuity of the curves and then check

the quality of the curves, you’ll be on your way to creating high quality surfaces.

Wireframe and Surface Analysis Techniques #2

This is the second in a series of articles discussing the tools available within CATIA to analyze the quality of surfaces and curves. The previous article discussed just wireframe analysis techniques.

This article will focus on analyzing the continuity and the quality of surfaces.

The procedure for analyzing surfaces is the same as analyzing wireframe. First check the

continuity of the surfaces and then check the quality. Once we have verified that we have an acceptable surface, then we can analyze the surface to check such things as minimum draft

angles and surface manufacturability. However, these topics will be discussed in the next article.

The first tool to look at is the surface connection checker. It is used to check the continuity of a

single surface or the interface between multiple surfaces. Simply select the type of continuity to check for, set a tolerance range and select the surface or surfaces to analyze. CATIA will then

determine the trouble spots, if any. In the example below (Fig. 1), we are looking for curvature

discontinuities that have a deviation greater than 5%. CATIA then highlights the problem areas (blue for curvature, yellow for tangency and red for point continuity) and displays the maximum

and minimum Curvature values. Curvature deviation varies from 0% to 200%. Ideally, curvature continuity should be as close as possible to 0%.

Figure1: Quick Surface Analysis Checker

The only problem with this quick analysis is it that while it correctly identifies the problem areas, along with the maximum and minimum extreme locations, it does not quantify the problem areas

along the entire interface. This is where the full analysis is beneficial. It uses a customizable color palette. All edges of the surfaces are color-coded based on the magnitude of the deviation. In fig.

2, the blue areas identify tangent continuities; the purple areas represent a maximum deviation

of greater than 2 degrees. Notice the areas of yellow and green which identify varying degrees of tangency discontinuity, more than 0 degrees, but less than 0 degrees.

Figure 2: Full Surface Analysis Checker

Now that we have checked the continuity, the next step is to check the surface quality. The quickest and easiest check is a quick visual search. It isn't as accurate as some of the other

techniques, but it will identify any obvious defects. For best results, change the color of the

surface to a brighter color and adjust the light sources.

Figure 2: Visual Surface Quality Check

A visual analysis will not identify all problems on a surface, but CATIA has several tools to check surface quality. Before we look at the tools, we need to define surface curvature.

At any given point on a surface, curvature is measured in two directions. Gaussian curvature =

where R1 and R2 are the radius of curvature in each direction.

Figure 3: Gaussian Curvature defined

Gaussian Curvature can be positive or negative. If the curvature direction is the same for both

measurements, the curvature is positive. If the curvature directions are opposite, the curvature is negative. This represents a saddle point on the surface

Figure 4: Gaussian Curvature Direction

This tool is used to identify surface quality problems. It color codes the surface based on Gaussian Curvature at every point. The magnitude of the curvature is not too important. Rather,

what is more important is how the surface transitions from areas of low curvature to areas of high curvature. Try to avoid sudden large curvature changes. The colors should change gradually

over a larger area. When the transitions occur over a small area, the result will always be a

bumpy surface. If the transition occurs over a larger area, the result will be a smoother surface.

Figure 5: Gaussian Curvature

A sudden change in the color indicates a curvature discontinuity.

Figure 6: Gaussian Curvature - Discontinuities

In summary, CATIA has excellent tools to analyze surface quality. For anyone designing class-A surfaces, these tools are a must. In this article, we have looked at two of those tools. The

surfaces connect checker checks surface continuity and the Gaussian Curvature tool checks

surface quality. In the next article, we will look at the tools available to check for part manufacturability.

Wireframe and Surface Analysis Techniques #3

This is the Last in a series of articles discussing the tools available within CATIA to analyze the

quality of surfaces and curves. The first article discussed just wireframe analysis techniques. The second article focused on analyzing the continuity and the quality of surfaces. This article will

continue to focus on tools that will analyze surface quality.

The first tool to look at is the inflection Analysis Tool. It will identify the areas of the surface where the curvature direction changes (bump in the surface). In the blue area, curvature is the

same in both directions (positive). In the green area, curvature is reversed (negative). In the yellow, the curvature is 0, which represents a transition area. Sometimes inflection areas in a

surface are needed, but many times this represents an unwanted bump in the surface.

Figure 1: Inflection Analysis

Try to avoid areas of one color embedded inside the other color. If this occurs, investigate the area for possible defects. In the following example (figure 2), there are two green pockets

surrounded by blue. These green areas dip below the rest of the surface. This tool does not

quantify how big this problem is. It only points out that a problem exists. A Further analysis using

some of the other tools we have already discussed, such as Gaussian Analysis, would determine the severity of the problem.

Figure 2: Inflection Analysis – Problem areas

The intersection planes command cuts the surface to create cross sectional curves of the

surface. Use the compass to define the direction of the cuts. This tool allows you to control

where the cuts are taken, how many there are and how far apart they are. A Curvature Analysis can then be performed on each of these cross sectional curves.

Figure 3: Intersection Planes Analysis

The next two tools will analyze the manufacturability of the surfaced part.

The limited radius analysis tools is used to identify the areas of the part where the radius of curvature in either direction is too small, making it impossible to manufacture the part. For

example, in figure 4 we want to know if a 2mm tool can be used to machine the part. Anywhere

where the part is colored red indicates a radius of curvature of less than 2mm, which means it is impossible to machine this area with a 2mm tool. So for the red areas, we will need a smaller

tool size.

Figure 4: Limited Radius Analysis

The last tool to look at is the draft analysis tool. This tool quickly reveals if the part has enough draft to be removed from a mold. Use the compass to specify the pull direction,

which is the direction the mold will be removed from the part. Select the surface to analyze and specify the draft angle to analyze. The surface is then color-coded based on the results.

Green shows areas that have the minimum required draft. Red indicates the area where the draft is less than the minimum but greater then 0 degrees. Blue areas represent an undercut. At any

location on the surface, you can obtain exact draft angle information.

Figure 5: Draft Analysis

All of these analysis results are captured in the specification tree. This means they can be easily

modified, renamed, or hidden. They are also fully associated to the parent geometry. So if the original curve or surface is modified, the analysis results will be updated, removing the need to

recreate the analysis on the new surface. In the following example (Figure 6), notice how the cutting plane analysis is automatically updated when the surface is modified.

Figure 6: Modifications

In Summary, CATIA has the tools that can help you analyze not only the quality of a surface, but also the functionality of a surface. Hopefully, this series of articles has provided you with

techniques that you will be able to use to be more efficient and effective in your daily design

work with CATIA V5.