CATIA geometry and data mapping

Use the following sections to identify the mapping process used for geometry types and non-geometric data transferred between Alias and CATIA via the CAI file.

Supported Alias geometry types

The following Alias geometry types can be exported to CATIA. Non-geometry entities such as Lights, Cameras, Textures, Windows, Shaders and Animation are not supported by the translator. The numbers in the table entries refer to Notes for table 1below.

Notes for table 1

1. The scale component of the Alias Construction Plane is not transferred. That is, its orientation and position will remain the same, but its size will not. After a round trip translation (Alias > CATIA V4> Alias), an Alias Construction Plane with original scale values Sx, Sy, and Sz, will return with scale values of 1, 1, 1.
2. An Alias Line created by Curves > Line and related tools is not supported on export to CAI as a CAI Line primitive, but is supported as a CAI BsplineCurve. However, on import to Alias of a CAI Trimmed Curve whose basis curve is a CAI Line (this maps to a CATIA V4 limited Line), an Alias Line is created. Such a Line will be exported as a CAI Line. This ensures the original CATIA V4 limited Line is preserved.
3. An Alias Face element is converted to a Trimmed Surface temporarily and then exported as such (see note (5) below).
4. An Alias Target Surface contains one or more Curves-on-Surface. A CrvSrf entity is exported for each curve-on-surface. On import to Alias, multiple CrvSrf entities that reference the same base surface will be converted to one Alias Target Surface containing multiple curves-on-surface that correspond to these CrvSrf entities.
5. An Alias Trimmed Surface is exported as one or more FaceElements (one FaceElement for each region of the trimmed surface). On import to Alias, multiple FaceElement entities that reference the same base surface are converted to an Alias Trimmed Surface, with multiple regions corresponding to these FaceElements.

• An Alias Trimmed Target Surface also contains curves-on-surface that have not yet been used for trimming. Similar to the descriptions in Notes 2 and 3, it is exported as a combination of CrvSrf and FaceElement entities.

Identifying CATIA V4 geometry and data mapping entities

To identify supported CATIA V4 geometry and data mappings use the following tables to identify the mapping process used for geometry types and non-geometric data transferred between Alias and CATIA V4 via the CAI file. The definitions for the letters and numbers in parentheses is provided below the table.

Notes for CATIA entities in table 2

1. For all CATIA curves whose limits have been modified, a CAI Trimmed Curve instance may be created when exporting.
2. For CATIA planar faces, some 4.24 planes may be transferred as they are used as the base face surface.
3. The curve associated with the edge in CATIA is converted into a B-spline Curve, used by the Oriented Edge. The parametric definition of the CATIA edge is converted to a B-spline Pcurve used by the Oriented Edge.
4. The domains of the CATIA volume are converted to open shells.
5. The Boundary representation of the solid is extracted and converted to CAI elements (open shells, curves, and so on). Prior to exporting the exact solid, make sure that this solid is up-to-date.

Notes for Alias entities in table 2

1. A CAI Point is converted to a degree 1 curve composed of two coincident points and a Locator that identifies the location of this curve. On export to CAI, this construction is converted back to a CAI point.
2. A CAI Plane describes an infinite plane and is converted to a unit Alias Surface. This Surface will be re-exported as a CAI Plane.
3. The CAI Oriented Edge maps to a trim curve of a trimmed region of an Alias Trimmed surface.
4. A CAI CrvSrf entity maps to one Alias curve-on-surface for a particular surface. Multiple CAI CrvSrf entities in the CAI file referencing the same surface will cause multiple Alias curves-on-surface to be added to one Alias Target Surface.
5. A CAI FaceElement maps to one region of an Alias Trimmed Surface. If multiple CAI FaceElements in the CAI file reference the same surface, then an Alias Trimmed Surface will be created with multiple regions.
6. A CAI Ditto is imported as an Alias instance node, with the CAI Ditto transformation, of the Alias group representing the CAI Detail (see Supported Non-Geometric Data, Groups/Instances below).

   However, if at least two CAI Dittos of the same CAI Detail each belong to different parent CAI details, then those dittos are “exploded”. That is, each geometric entity of the detail is copied and transferred by the transformation of the CAI Ditto.

Supported non-geometric CATIA data

The following non-geometric data can be imported and exported between Alias and CATIA.

Groups/instances

How an Alias Group is exported depends on whether it is instanced or not. An Alias Group that is not instanced has its component geometry exported to the appropriate independent CAI geometric entities. An Alias Group node that is instanced is exported as a CAI Detail entity (that is, the grouped Alias geometric entities become members of the CAI Detail); an Alias Instance node is exported as a CAI Ditto entity. CAI Dittos and Details are subsequently imported into CATIA as CATIA Dittos and Workspaces, respectively.

An Alias Instance that contains a non-proportional (non-p) scaling factor in its transformation is “exploded” on export (that is, each geometric entity that belongs to the Alias Group being instanced is copied and transformed to independent CAI geometric entities). Only instances that contain a non-p scale component are exploded. Other instances of the same group that do not have a non-p scale component will export as CAI Dittos of a CAI Detail (as noted above).

CATIA Workspaces and Dittos can feature a situation that is not supported by the Alias dag structure and instancing mechanism. This situation arises when Dittos of the same Workspace belong to different parent Workspaces (see note (6) in Notes for Alias entities in table 2 above). The CATIA Ditto/Workspace structure is preserved as best as possible on CAI export from CATIA and subsequent import back to CATIA.

Names

Alias DAG node names are exported as an attribute of the CAI entity to which the node’s geometry maps. Alias Instance node names are exported as an attribute of the CAI Ditto; the corresponding CAI Detail will have the name of the instanced Alias Group node. The name attribute of a CAI entity is mapped to the CATIA User Identifier for that entity in CATIA.

On CAI import to Alias, it is possible for multiple CAI entities to map to a single Alias object (see notes (4) and (5) in Notes for Alias entities in table 2 above). Each of these CAI entities may have a unique name (CATIA User Identifier), but the Alias object can only have one name available for viewing and editing. The CATIA User Identifiers that are not mapped to an Alias object with a modifiable name are maintained by Alias for subsequent export to CATIA via CAI, assuming the objects to which the names are assigned still exist.

For example, a CATIA user can name individual Faces that all reference the same surface. These Faces map to CAI FaceElements which in turn map to trim regions of a single Alias Trimmed Surface. Only the trimmed surface node can have a name, and this is given the name of the underlying CATIA surface being trimmed. The CATIA User Identifiers of each of the faces that mapped to trim regions are maintained within Alias so they can be transferred back to CATIA. A similar situation exists for multiple CAI CrvSrf entities that map to one Alias Target Surface. The CAI CrvSrf name attribute is preserved for export back to CATIA.

Alias generated names of the form node#<n> (for example, node#5) are not exported to CAI. CATIA generated names of the form *<OBJ><N> (for example, *FAC5) are not exported to CAI. CAI entities that do not have names are given a system generated name on import to Alias or CATIA.

Layers

The Alias Layer assignment is preserved when exporting to CAI. As with names, the layer number becomes an attribute of CAI geometric entities and Dittos. The layer name and other Alias Layer attributes are not exported.

On CAI import to Alias, geometric entities are placed on the layer defined by the CAI layer number attribute. If the layer is created by the import process, it is given the name CATIA_<N> where <N> is the layer number. All layers created by the CAI import process are sorted in the layer bar by ascending number.

As with the name attribute, the layer number assignment for CAI FaceElement and CAI CrvSrf entities is preserved on CAI import so that this information can be returned to CATIA through CAI even though it cannot be modified in Alias.

In Alias, a geometric object and all of its ancestors in the dag hierarchy must be in the same layer. In CATIA, this is not necessarily the case, as a Ditto may be in a different layer than the components of the instanced Workspace. On CAI import to Alias, this feature of CATIA layers is maintained for subsequent export back to CATIA. If you change the layer assignment of an Alias Instance that was created from a CAI Ditto, you will change the layer assignment of all the geometric entities being instanced to this new layer number within Alias. However, on CAI export, the original CATIA layer number assignments for the component geometric entities and Ditto will be used.

CATIA Dittos that are not assigned to a layer will be preserved through a bi-directional CAI translation with Alias. While in Alias, these Dittos will be imported as Alias instances that reside in the Default Layer.

Object colors

The wireframe display color of CATIA objects is preserved in a bi-directional CAI translation with Alias, providing the CATIA model uses the CATIA Standard Color Table. If the model references a user-defined color table, then on CAI import to CATIA, the CAI color of each element is chosen from the standard color table as the closest match to the original color.

As with names and layers, the CATIA wireframe color index of an object is an attribute of the CAI geometric entity. On CAI import to Alias, the CAI geometric entity’s color index is converted to an RGB color based on the CATIA Standard Color Table. This RGB color is used to create a simple shader that is assigned to the associated Alias object that is created, unless the object is a curve. Only for curves is the CATIA wireframe color index preserved. CAI surface geometry that has no CAI color attribute is assigned the Alias default shader.

On Alias export to CAI, the color index of a CAI geometric surface is determined by finding the index in the CATIA Standard Color table that represents the closest match to the RGB color of the associated Alias shader. For non-surface CAI entities, the preserved CATIA color index is exported if it exists. For original Alias curve geometry, the layer color is used to find a close match to a CATIA Standard Color index.

Layer colors

Layer colors are not transferred explicitly via the CAI format. However, layer colors are assigned to layers created as a result of CAI import by one of two possible methods.

In the first method (the default) a created layer is assigned one of the 15 available colors based on the remainder of the layer number divided by 15. This cycles through the available Alias layer colors as the layer number increases.

The second method uses the CATIA Standard Layer Color Table which is defined in the CATIA environment’s startup initialization file CATINSTD.dcls. If this file exists in the /usr/aw/alias/.Alias/ directory of the Alias installation, or in the.Alias/Prefs.1/Color/ directory of the Alias user account, then the CATIA Standard Layer Color Table will be extracted from this file by the Alias CAI import process and used in the layer color assignment process.

The CATIA Standard Layer Color Table assigns to each of the 256 CATIA layers a default CATIA color index whose RGB color is defined in the CATIA Standard Color Table (see Object colors above). When the Alias CAI import process has access to this default layer color assignment, it assigns a color to a newly created Alias layer that closely matches the color for that layer number in the table.

To activate this second method copy the CATINSTD.dcls file from the CATIA installation to /usr/aw/alias/.Alias/ or to the .Alias/Prefs.1/Color directory of your user account. Alternatively, create a symbolic link, in either of these Alias directories, to the CATINSD.dcls file in the CATIA installation.

For example, if Alias is installed in /usr/aw and CATIA is installed in /usr/catia, then the following command will create the necessary symbolic link:

ln -s  /usr/catia/cfg/dec/CATINSTD.dcls /usr/aw/alias/.Alias/CATINSTD.dcls

What happens when creating a skin and offsetting for CATIA?

Creating a ‘skin’ and ’offsetting’ (or creating solid geometry from imported Alias models) is a common workflow when integrating Alias and CATIA. When exporting the model from Alias, you must ensure that the geometry is built to the correct tolerance and that it can also be stitched. The stitching process in Alias identifies gaps between surfaces so that you can repair the appropriate geometry before writing the file out to CATIA.

During stitching, the surfaces are twinned. This means that the surface boundaries may be split to accommodate adjacent surfaces, and periodic geometry is detached into multiple surfaces. For this reason, you should save the Alias wire file before stitching so that if further modifications are required to be made to the Alias model, the construction history will be intact.