Assemblies And Instances

22.1 Introduction

Assemblies and instances in the PK are primarily provided to enable applications to transfer assembly information via Parasolid transmit files. It is not intended to provide complex assembly modeling capability in Parasolid.

See Chapter 100, “Archives”, for further information about Parasolid transmit files.

22.1.1 What is an assembly?

An assembly is a collection of instances of parts (parts are bodies or assemblies):

Assemblies may also contain construction geometry (surfaces, curves and points).
Assemblies may have attributes attached.
A group owned by an assembly may only have instances and construction geometry of the assembly as members.
An assembly graph must be acyclic, i.e. an assembly may not instance itself, directly or indirectly.
An assembly cannot instance a part in a different partition.

22.1.2 What is an instance?

An instance is a pointer to a part contained within an assembly:

An instance refers to its owning assembly, the part it instances, and a transform.
An instance has an integer entity-id; the instances directly referenced by an assembly have distinct entity ids.
An assembly may contain any number of instances of the same part.
Instances cannot exist outside an assembly, and the part they instance must not be null.

22.1.3 What is a transform?

A transform positions a part in the coordinate frame of an assembly:

Transforms attached to instances must be a rigid motion or a reflection (see Section 14.2.9, “Assembly”).
If the transform is null, it is treated as the identity transform.
Transforms may not be shared by instances.

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22.2 Transmit files

A Parasolid transmit file (part file) contains one or more non-instanced parts, together with all their sub-parts, down to the bodies at the bottom level. These assembly graphs are disjoint, i.e. they have no common parts.

22.2.1 Part names

The system-defined name attribute (SDL/TYSA_NAME) may be used by applications wishing to attach a textual name to identify parts in a part file. Alternatively, the entity ids of the instances may be used to reference particular instances in a part file.

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22.3 PK functions

The following functions can be used to create, modify and request information about assemblies.

22.3.1 Creation and modification functions

Function	Description
PK_ASSEMBLY_create_empty	creates an empty assembly
PK_INSTANCE_create	creates an instance, given a standard form containing assembly, transform and part
PK_INSTANCE_change_part	alters the instance to instance a different part
PK_INSTANCE_replace_transf	replaces the transform of an instance
PK_ASSEMBLY_transform	transforms an assembly by transforming all its instances
PK_INSTANCE_transform	transforms an instance by transforming its transform

PK_ASSEMBLY_make_level_assembly

Creates a new one-level assembly which is a flattened version of the given assembly. The new assembly contains new instances and transforms, but instances existing parts. There is one instance in the new assembly, for each path from the given assembly down to a body at the bottom level of the assembly graph.

22.3.2 Navigation functions

Function	Description
PK_ASSEMBLY_ask_parts	returns the parts directly instanced by an assembly, with duplicates if a part is instanced more than once
PK_ASSEMBLY_ask_instances	returns the instances directly referenced by an assembly
PK_ASSEMBLY_ask_parts_transfs	returns the parts and transforms corresponding to the instances directly referenced by an assembly
PK_INSTANCE_ask	returns the standard form of an instance, which consists of its owning assembly, referenced part, and transform
PK_PART_ask_ref_instances	returns the instances which instance the given part