Links in CATIA, Part 3: Context Link

Julie Cyrenne, Dassault Systemes

Introduction

In the previous article, we saw how to do design in context, where the child part (also known as contextual part) utilizes elements from the parent part to complete its geometrical definition. As a result, the parent part has no external link while the child part has 2 external link types: import and context. This article will explain when and how the context link is created. All the concepts will be illustrated using the example of a spline.

The Context Link
In CATIA V5, a context link is created when an import link is created in a CATPart. However, there may only be one context link per part, regardless of the number of import links. The context link points from a CATPart (the child) to a CATProduct (the parent).

Figure 1: Edit/ Links panel showing 5 import links but only one context link

The context is the product in which a part designed in context is associatively designed. In other words, if this product is opened, all the parent parts of the contextual part (part with import links) will be present and all the links will be resolved. You can also think of the context as the entity which needs to be opened for synchronizing links and updating a contextual part.

Choosing a context
In Tools/ Options/ Infrastructure/ Part Infrastructure/ General, there is one option associated with the context link: ‘Use root context in assembly’.

Figure 2: 'Use root context in assembly' option

When the option ‘Use root context in assembly’ is not selected, the minimum context is used. In other words, when creating a part’s first import link, the first product that is a common parent of the two parts involved in the link becomes the context of the contextual part. The two left cases in Figure 3 below illustrate the result of using the minimum context.

When the option ‘Use root context in assembly’ is selected, the root product opened in session becomes the context of the child part. The right case in Figure 3 below illustrates the result of using the root context.

Figure 3: Impact of the 'Use root context in assembly' option

Once the context link is created, it does not change if the contextual part is opened in another configuration (unless explicitly changed by the designer as described in the ‘Managing the context’ section)

Considerations when choosing a context
1) It is impossible to create links with parts outside the context

In the example below, the Profile part contains a sketch of an I-beam profile. The Beam part is a pad using the Profile’s sketch, hence creating an import link in the Beam part. The context link of the Beam points on Product2, as the ‘use root context in assembly’ was not selected. Later, if the designer wants to split the Beam with the Surface, he will get an error message (Figure 5 and Figure 6). Since the Surface part is outside Product2 (the context), it is impossible to create an import link from the Beam to the Surface.

Figure 4: Example for 'impossible to create links outside the context'

Figure 5: Pop-up message when trying to select an object outside the context for contextual design

Figure 6: Error message when trying to paste with link an element from outside the context

2) It is impossible to update links if the context is not loaded in session

In the example below, the Cylinder is a pad defined up to the Surface part. The import link points from the Cylinder to the Surface. Since the option ‘use root context in assembly’ was active when the import link was created, the context link points from the Cylinder to the Product1. If a designer wants to work in Product2, any modification to the Surface will not be represented in the Cylinder because the context product is not in session (even though all the parts involved in the import link are loaded in session).

This example shows how, in a context of concurrent engineering, the root context should be used with caution!

Figure 7: Modification and update of a contextual part outside its context

3) In specific use cases, it may be mandatory to work with a specific context

I don’t want to enter into details as this is outside the scope of this article, but an example is when building a ‘structure exposed’ assembly in ENOVIA, the root context must be used,

Managing the context
It is possible to change the context of a part to a higher level or a lower level product.

Open Right-click on the part whose context should be changed, go to ‘Components’ and ‘Define Contextual Links’. In the panel that appears, simply click on OK. The new context of the part will be the active product in session (regardless of the option ‘use root context in assembly’)

Figure 8: 'Define contextual links' panel

Icons
There are four CATPart icons to inform on the part’s context. You may understand their purpose from the images in the examples. The next article will explain the meaning of each icon,

	Non-contextual part
	Definition contextual part
	Instance of the definition contextual part
	Instance of a contextual part

The spline example
Two designers are working in their separate assemblies, Product_A and Product_B.

In Product_A, the first CATPart, Points_A, contains 5 points that are published. The second CATPart, Spline_A, has import links to the 5 points as it uses them for the definition of the spline. Whether the option ‘use root context in assembly is enabled or not is irrelevant: because Product_A only has one level, the context link points to Product_A in either case.

Product_B is architected the same way.

Figure 9: The spline example: designer's initial state

Once both designer’s work is done, the two products are inserted in a higher level product, Integration_A-B. The two splines must be connected by using the last point of Point_A as a point for Spline_B. The figure below shows how the software will not allow this operation.
Figure 10: The spline example: Spline_B's context does not allow to import with link elements from Points_A

In order to enable this operation, the context of Spline_B should be changed from Product_B to Integration_A-B using ‘Define Contextual Links’. Once the context is changed, Figure 12 shows how the operation will be allowed. The context of Spline_A does not need to be changed: the part does not have any external links outside Product_A to create.

Figure 11: The spline example: changing the context of Spline_B

Figure 12: The spline example: Spline_B successfully imported with link an element form Points_A

Conclusion This article explained the context link and the means to manage it. There is no good or bad way: it depends on concurrent engineering, data architectures, etc.

One useful source of information to interpret the context is the CATPart icon. This will be explained in the next article.

Julie Cyrenne
Dassault Systemes
Julie Cyrenne

What kind of surface do I need?
Nathan Haller, MSC.Software Corporation

With the wide variety of surfacing tools available in CATIA V5, how do you know which tool to use and when?

Surface geometry can be generated in a variety of different ways. Some methods are unique to the program generating the surfaces while other methods have been used and proven over the years. When creating a surface, you should consider not only the capability of your software tools but also how and where the surface is going to be used. CATIA V5R14 has seven primary shape design products. Each product is different in its functionally and intended use.

Generative Shape Design 2 (GSD) is one of the more widely used products. It helps to design advanced wireframe1 and surface1 geometry with fully associative specifications. GSD is a feature-based design environment for the capture and reuse of analytical1 design methodologies and specifications. See example in Figure 1.

GSD is commonly used as an alternative or complement to solid modeling tools, resulting in a “hybrid1” modeling scheme. Laws and knowledgeware built into GSD provide productivity enhancing functionality to create complex surfaces even faster. GSD has tools that allow the user to create free-form1 spline1 curves and conic curves. It also has the ability to control point, tangency, and curvature continuity1 between curves and surfaces.

Generative Shape Optimizer (GSO) is added on top of GSD and gives the designer access to smart tools that allow for faster shape deformation. GSO also adds productivity gains suitable for automotive design with the addition of variable offsets on a complex shell.

Figure 1: Example of GSD in use.

Freestyle Shaper (FSS) is used to generate aesthetic1 non-associative (datum) 3D curves and surfaces from scratch, and to dynamically deform and analyze all produced elements. See example in Figure 2. FSS uses control points1 to control the continuity1 between elements and to adjust curve and surface curvature. The quality of the curves and surfaces can be checked using industry-oriented diagnostic tools.

In addition to FSS, Freestyle Optimizer (FSO) adds global deformation of multiple surfaces and the ability to “fit” geometry to physical mock-up scan data.

Figure 2: Example of FSS in use.

Automotive Class A (ACA) is an industry specific product used to create “Class A” surfaces that meet or exceed strict tolerance and smoothness requirements. Similar in methodology to Freestyle Shaper, ACA surfaces can obtain G3 continuity matching, or the rate of change of curvature continuity. ACA has some associativity when creating and modifying elements, but the end results are usually non-associative. See example in Figure 3.

In addition to ACA, Automotive Class A Optimizer (ACO) can be added for global deformation capabilities on multiple surfaces.

Figure 3: Example of ACA in use.

Imagine and Shape 2 (IMA) is used to capture and make tangible the conceptual phase of aesthetic1 product development. See example in Figure 4. Complemented by Freestyle Sketch Tracer (FSK), IMA is based on mathematical “subdivision1” technology: an algorithmic technique to generate smooth surfaces as a sequence of successively refined polyhedral meshes. This will allow you to form your concept from a sphere, a flat surface, or a curve. IMA is quite possibly the future of CAD modeling.

Figure 4: Example of IMA in use.

Freestyle Sketch Tracer (FSK) is used to convert 2D images into a 3D scene in order to create 3D geometry from your hand drawings or other sources such as pictures. Once added, the images are able to move normal to the positioning plane. The designer can then use products like Generative Shape Design, Freestyle Shaper, or Automotive Class A to generate the geometry. FSK works with JPG, BMP, TIFF and RGB files. See example in Figure 5.

Figure 5: Example of FSK in use.

Digitized Shape Editor (DSE) is not used to create geometry, rather it is used to import and process digitized point clouds1. The point cloud can be tessellated1 for quick visualization of the imported polygon mesh1. DSE is a vital component in the reverse engineering process. Once the cloud is imported and adjusted to suit your need, Generative Shape Design, Freestyle Shaper, Quick Surface Reconstruction, or Automotive Class A can be used to generate the geometry. See example in Figure 6.

Figure 6: Example of FSK in use.

Quick Surface Reconstruction (QSR) allows you to create prototype quality surfaces from digitized data that has been cleaned up and tessellated using Digitized Shape Editor (DSE). Essentially a “shrink wrapper” is produced based on user defined tolerances1. In addition to organic shapes, QSR will detect and create mechanical shapes (plane, cylinder, sphere, and cone). The resulting surfaces are datum (non-associative). See example in Figure 7.

Figure 7: Example of QSR in use.

In summary, for surfaces in a hybrid environment that are fully associative, Generative Shape Design is the product you should choose. If you need more flexibility in aesthetics, then Freestyle Shaper is your choice. For flexibility in aesthetics with high tolerances for Class A surfaces, then the Automotive Class A product should be your choice. To quickly construct surfaces from point cloud data, you’ll want to invest in Quick Surface Reconstruction.

“Surfacing” Lexicon