Creating Extruded Bodies

Contents

• 37.1 Introduction
• 37.2 Supplied arguments
  • 37.2.1 Profile types
  • 37.2.2 Specifying the start and end of the extrusion
  • 37.2.3 Supplying an extruded body
  • 37.2.4 Returning disjoint bodies
  • 37.2.5 Consistent parameterisation
  • 37.2.6 Extruding facet bodies
    • 37.2.6.1 Preventing mixed bodies
• 37.3 Bound types
  • 37.3.1 PK_bound_distance_c
  • 37.3.2 PK_bound_surf_c
  • 37.3.3 PK_bound_face_c
  • 37.3.4 PK_bound_body_c
  • 37.3.5 PK_bound_sheet_c
  • 37.3.6 PK_bound_none_c
• 37.4 Tracking information
  • 37.4.1 Extruded entities
  • 37.4.2 Bounding entities
• 37.5 Dealing with multiple intersections of the extruded body
• 37.6 Dealing with profiles that intersect the first division
• 37.7 Examples of extrusion

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37.1 Introduction

Creation of extruded bodies is supported via PK_BODY_extrude. This function creates a body by linear extrusion of a profile body. The profile body may be a minimum body, a wire body or a sheet body. These profiles create extruded wire bodies, sheet bodies or solid bodies respectively. The start and end of the extrusion can be specified in a number of ways; in particular by intersection with other bodies.

The direction of extrusion is defined by a unit vector. The start and end of the extrusion (the bounds) must be ordered along this vector so that the start comes first.

Figure 37-1 Extruding a profile to create an extruded body between two bounding faces

There are several ways of defining the start or end of an extrusion:

For more information on these options, see Section 37.3, “Bound types”.

PK_BODY_extrude returns tracking information that shows which entities have given rise to entities in the resulting extruded body. For more information, see Section 37.4, “Tracking information”.

For an example of this functionality, see the code example in the C++\Code Examples\Modelling\Profiling\Extrude folder, located in example_applications in your Parasolid installation folder.

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37.2 Supplied arguments

The following arguments are supplied to PK_BODY_extrude:

profile

path

options

37.2.1 Profile types

Several different types of profile body can be passed to PK_BODY_extrude, each of which creates a different type of extruded body. The supplied profile cannot be a general body.

A sheet profile must be a connected manifold sheet body. It may have multiple laminar boundaries.

37.2.2 Specifying the start and end of the extrusion

The start and end of the extrusion are specified in the PK_BODY_extrude_o_t structure. Two bounds must be supplied, and they are both specified in the same way, as described in the table below.

For each bound (whether start or end) the following information is required:

bound

forward

distance

entity

nearest

nth_division

side

37.2.3 Supplying an extruded body

Rather than let Parasolid extrude a profile, there may be times when you have already created a body using a sweep or extrusion operation (for instance, a tapered extrusion created using PK_BODY_sweep and PK_BODY_taper), and you want to trim it using the powerful bounding functionality provided by PK_BODY_extrude. You can do this by supplying the body using the extruded_body option in PK_BODY_extrude_o_t. An example of the intended use of this option is shown in Figure 37-2.

Figure 37-2 Supplying an extruded body for trimming

If you supply an extruded_body , then you should supply the profile used to create that body as the profile for PK_BODY_extrude. If the profile lies within the extruded_body (i.e. if the start bound is backward and the end bound is forward) then it should be an exact section that fully intersects the extruded_body . This lets you specify a region to include, and is necessary to resolve any ambiguities where multiple solutions are possible.

37.2.4 Returning disjoint bodies

You can use allow_disjoint in PK_BODY_extrude_o_t to specify whether disjoint components can be returned by PK_BODY_extrude. By default, disjoint components are not allowed: if the resulting extruded body contains several components, PK_BODY_extrude returns PK_ERROR_disjoint. To return a single body containing several disjoint components in such cases, set allow_disjoint to PK_LOGICAL_true.

37.2.5 Consistent parameterisation

You can use consistent_params to specify whether or not the v-parameter of an extruded plane is aligned with the sweep direction of the extrude operation. By default, it is set to PK_PARAM_consistent_unset_c. Figure 37-3 illustrates the result of an extruded plane when consistent_params is set to either value.

Figure 37-3 Extruded plane with its v-parameter aligned with the sweep direction

37.2.6 Extruding facet bodies

If the supplied profile contains facet geometry you can control how the resulting extruded body is split and model edges are created using the have_pline_angle and the pline_angle options.

The pline_angle is the maximum angle between the polyline segments of the profile that will result in a model edge being created in the extruded body.

If the have_pline_angle option is set to PK_LOGICAL_true, and the angle between adjacent polyline segments, when viewed down the extrude direction, is greater than or equal to pline_angle then an additional model edge is introduced to the extruded body which splits the body at that position.

37.2.6.1 Preventing mixed bodies

You can control the geometry types of the resulting body if the input body contains facet geometry only.

The keep_as_facet option controls the geometry type of the extrusion, and determines whether the result body contains only facet geometry, or a mixture of classic and facet geometry.

See Section 84.6, “Creating a mixture of facet and classic geometry”, for more information.

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37.3 Bound types

This section describes the different types of bound that can be defined.

37.3.1 PK_bound_distance_c

The bound is produced by creating a copy of the given profile shifted along the path vector by the given distance. The distance must be non-negative. To extrude in the opposite direction to the path vector the forward field of the bound is set to PK_LOGICAL_false.

Figure 37-4 Extruding a profile a specified distance

37.3.2 PK_bound_surf_c

The bound is produced by trimming the extruded body to a surface. Either a surface or a face can be supplied. If a face is supplied then its surface is used, but divisions are not restricted to the region of the underlying surface that the face occupies. The surface is unaffected by the operation.

Figure 37-5 Extruding a profile to a surface

37.3.3 PK_bound_face_c

The bound is produced by trimming the extruded body to a face. If the face does not completely trim the extruded body, then adjacent faces are used to trim the body. The faces are unaffected by the operation.

Figure 37-6 Extruding a profile to a face

37.3.4 PK_bound_body_c

The bound is produced by trimming the extruded body to a sheet body or solid body. Parasolid selects suitable faces for bounding the extrusion. The body is unaffected by the operation.

Parasolid finds all collections of faces that may intersect the extrusion.

Figure 37-7 Extruding a profile to a bound created by intersection with a body

37.3.5 PK_bound_sheet_c

Like PK_bound_body_c (when given a sheet body), the bound is produced by trimming the extruded body to a sheet body. However, the sheet body itself is destroyed by the operation. All faces of the given sheet body are used in finding the bound.

37.3.6 PK_bound_none_c

This bound is exclusively for use when you specify an existing body using the extruded_body option, rather than let Parasolid create one from a profile. Using this bound indicates that the corresponding end of the extruded_body should not be altered by the extrude operation.

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37.4 Tracking information

PK_BODY_extrude provides tracking information that shows which entities have given rise to entities in the resulting extruded body. Tracking is provided for both:

• Extruded entities, i.e. entities that have been created as a result of extruding from the profile.
• Bounding entities, i.e. entities that have been created as a result of the extruded result intersecting with a bounding entity.

In any result body, a given entity may be considered to be both an extruded entity and a bounding entity, and so may be tracked from more than one source.

37.4.1 Extruded entities

For extruded entities, the tracking information returned is as follows:

37.4.2 Bounding entities

For all bound types except PK_bound_distance_c, bounding entities are created where the extruded body intersects a bounding body. The bounding entities are tracked from what they intersected. The nature of bounding entities created depend on the type of profile supplied:

The tracking information returned for bounding entities depends on the nature of the bound:

If you extrude a wire profile and also specify an extruded_body , then each edge of the result body that is not a bounding edge is tracked from the edge of the given extruded_body in the same position. This is because the tag of the edge of the result body may not be the same as the tag of the edge of the extruded_body .

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37.5 Dealing with multiple intersections of the extruded body

A given bounding entity (such as a sphere) may intersect the extruded body at several places. When this occurs, use nth_division and nearest to determine which intersection should be used as the bound. The way that intersections in the bounding body are numbered also depends on the value of forward .

When nearest is PK_LOGICAL_true, divisions are numbered from the profile outwards, so that the first intersection is the nearest. The reverse is true if nearest is PK_LOGICAL_false, as shown in Figure 37-8.

Figure 37-8 Using nearest to reverse the direction of division numbering

When forward is PK_LOGICAL_false, the extrusion occurs in the opposite direction, and divisions are numbered as shown in Figure 37-9.

Figure 37-9 Division numbering when extrusion occurs in the opposite direction

Bounds can only occur at a division that goes right across the extruded profile. Intersections with the extruded profile that do not completely cross the extrusion are ignored.

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37.6 Dealing with profiles that intersect the first division

In cases where the profile (or a distance bound from the profile) intersects the first division on a bounding body or face, extruding the profile may yield several different solutions. Figure 37-10 shows an example (in cross-section) where several extrusions are possible as a result of extruding a profile from the first division of a bounding body.

Figure 37-10 Multiple solutions possible due to profile intersecting division

You can use the side field in either the start or end bound to specify which side of a bounding entity should be in the first division when extruding. This field can take the following values:

Figure 37-11 illustrates the bodies that would be extruded from the example in Figure 37-10 for each of these values.

Figure 37-11 Specifying which solution should be used

Figure 37-12 shows a number of additional examples. In each one, the start bound is left at its default setting: a distance bound of 0. The end of the extrusion is bound by the bounding body shown. The examples demonstrate the different extruded bodies that can be created using different values in the side field of the end bound.

Figure 37-12 Extruding using profiles that intersect the bounding body

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37.7 Examples of extrusion

In the following examples, only an end bound of type PK_bound_body_c is supplied. The profile and the bounding body are as shown in Figure 37-13. The path is from the profile directly towards the bounding body. Resulting extruded bodies are shaded.

Figure 37-13 Profile and bounding body used in subsequent examples

Figure 37-14 Extruding to the nearest and furthest bounding faces

Figure 37-15 Extruding in to the second nearest and second furthest bounding faces

In the following examples, both a start bound and an end bounds are specified. Both bounds are of type PK_bound_body_c. The profile and bounding body shown in Figure 37-13 are used.

In Figure 37-16, the profile is extruded from the nearest division to the furthest division. Note that the profile is not contained in the resulting extrusion.

Figure 37-16 Extruding from the nearest bounding face to the furthest bounding face

You can achieve the same effect by placing the profile between the bounds and extruding as far as possible in each direction

Because the start bound must come before the end bound, if you request start and end bounds at the same division, the end bound that Parasolid chooses is at the first division after the start bound, as shown in Figure 37-17.

Figure 37-17 Extruding to identical start and end bounds

Figure 37-18 demonstrates extruding across an intersection that does not go right across the profile. In such cases, the intersection is not considered to be a true division. Note that the extruded body could be further modified by setting the side field in the start bound, as described in Section 37.6, “Dealing with profiles that intersect the first division”.

Figure 37-18 Extruding across an incomplete intersection to the nearest bounding face

If you extrude a wire profile to create a sheet body, each extruded face may intersect with a bounding body a different number of times. This can lead to different result bodies, depending on the division that you choose to extrude to.

Figure 37-19 shows an example in which a square wire profile is extruded until it intersects a cylinder with a diameter that is equal to the length of an edge in the profile. In this example, some faces intersect with the bounding body once, while other faces intersect twice. You can produce different results, depending on whether you select the first or second division.

Figure 37-19 Specifying different divisions when extruding wire profiles

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