About This Manual

Contents

• 1.1 Introduction to the XT format
  • 1.1.1 Parasolid XT format terminology
  • 1.1.2 Types of file document
  • 1.1.3 Text and binary formats
  • 1.1.4 Standard file names and extensions
  • 1.1.5 The alternative solution

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1.1 Introduction to the XT format

This XT data Format manual describes the formats in which Parasolid represents model information in external files. Parasolid is a geometric modeling kernel that can represent wireframe, surface, solid, cellular and general non-manifold models.

Parasolid stores topological and geometric information defining the shape of models in transmit files. These files have a published format so that applications can have access to Parasolid models without necessarily using the Parasolid kernel. The main audience for this manual is people who intend to write translators from or to the Parasolid transmit format.

Reading and writing transmit data are significantly different problems. Reading is simply a question of traversing the transmit file and interpreting the records stored within it. Writing is a significantly harder process; as well as getting the data format of the transmit file correct applications must also ensure that the many complex and subtle inter-relationships between the geometric nodes in the file are satisfied.

The presentation of material in this manual is structured to help the construction of applications that perform read operations. It is strongly advised that the construction of applications that write files is only attempted when a copy of Parasolid is available during the development process to check the consistency and validity of files being produced.

This manual documents the XT data format. This format will change in subsequent Parasolid releases at which time this manual will be updated. As new versions of Parasolid can read and write older XT data formats these changes will not invalidate applications written based on the information herein.

1.1.1 Parasolid XT format terminology

Some of the terminology used in the XT data format differs from that used in the documentation for Parasolid. The following table lists these differences:

1.1.2 Types of file document

There are a number of different interface routines in Parasolid for writing XT data. Each of these routines can write slightly different combinations of Parasolid data, the ones that are documented herein are:

• Individual components (or assemblies) written using SAVMOD
• Individual components written using PK_PART_transmit
• Lists of components written using PK_PART_transmit
• Partitions written using PK_PARTITION_transmit

The basic format used to write data in all the above cases is identical; there are a small number of node types that are specific to each of the above file types.

1.1.3 Text and binary formats

Parasolid can encode the data it writes out in four different formats:

• Text (usually ASCII)
• Neutral binary
• Bare binary (this is not recommended)
• Typed binary

In text format all the data is written out as human readable text, they have the advantage that they are readable but they also have a number of disadvantages. They are relatively slow to read and write, converting to and from text forms of real numbers introduces rounding errors that can (in extreme cases) cause problems and finally there are limitations when dealing with multi-byte character sets. Carriage return or line feed characters can appear anywhere in a text transmit file but other unexpected non-printing characters will cause Parasolid to reject the file as corrupt.

Neutral binary is a machine independent binary format.

Bare binary is a machine dependent binary format. It is not a recommended format since the machine type which wrote it must be known before it can be interpreted.

Typed binary is a machine dependent binary format, but it has a machine independent prefix describing the machine type that wrote it and so can be read on all machine types.

1.1.4 Standard file names and extensions

Due to changing operation system restrictions on file names over the years Parasolid has used several different file extensions to denote file contents. The recommended set of file extensions is as follows:

• .X_T and .X_B for part files .P_T and .P_B for partition files.

Extensions that have been used in the past are:

• xmt_txt , xmp_txt - text format files on VMS or Unix platforms
• xmt_bin , xmp_bin - binary format files on VMS or Unix platforms

1.1.5 The alternative solution

An alternative solution for reading and writing XT data is to license the Parasolid software, which is available in Designer, Editor, Communicator and Educator packages.

For further details on these packages, and contact information, visit the Parasolid website at http://www.parasolid.com

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