ACIS3D几何建模引擎入门指南

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"该资源是关于ACIS（Advanced Computer Aided Interoperability Solutions）的参考文档，虽然以英文形式呈现，但具有很高的参考价值。ACIS是一个由Spatial Corp.开发的面向对象的三维（3D）几何建模引擎，常被用作各种3D建模应用的基础几何框架。该引擎由C++编写，提供了线框、曲面和实体建模的开放架构，基于统一的数据结构。" 在"Chapter 1 Introduction"中，文档首先对ACIS进行了简要介绍，强调了它作为3D几何建模的核心组件的角色。ACIS设计用于支持各种最终用户3D建模应用程序，并提供了一个统一的平台，以处理从线框模型到表面模型再到实体模型的各种几何构建。 "3D ACIS Fundamental Concepts Guide"是进一步了解ACIS的关键资料，它涵盖了使用ACIS的基础概念，如几何学、拓扑学、公差、曲线和曲面等。这本指南深入解释了ACIS如何利用C++语言进行编程，为开发者提供了重要的理论背景和实践指导。 "3D ACIS Glossary"是ACIS及相关几何建模术语的词汇表，对于理解和学习ACIS的专用术语非常有帮助。通过查阅这个词汇表，读者可以更准确地理解文档中的专业术语，提高阅读效率。 "3D ACIS Online Help User’s Guide"则详细介绍了如何使用在线帮助系统。这个指南对于那些需要快速查找特定功能或解决问题的用户来说，是非常实用的工具，它能够帮助用户高效地导航和利用ACIS的文档资源。虽然文档中提到Spatial不保证对对象的所有操作都有效，但这通常意味着在实际应用中，开发者需要理解和测试ACIS的各种操作，确保它们在特定场景下的正确性和稳定性。 ACIS参考文档提供了全面的ACIS介绍、基础概念、专业术语和在线帮助系统的使用方法，对于开发者和工程师而言，这是一个深入了解和掌握ACIS技术的重要资源。通过深入学习和实践，用户将能够有效地利用ACIS进行复杂的3D几何建模。

Getting Started Guide 8.0

Chapter 3.

SAT Save File Format

Topic: SAT Save and Restore

ACIS can store modeling information in external files, called save files. These files have an

open format so that external applications, even those not based on ACIS, can have access to

the ACIS geometric model.

The basic information needed to understand the ACIS file format (focusing on the reading, or

restore, operation), includes the structure of the save file format, how data is encapsulated, the

types of data written, and subtypes and references.

Save File Types

Topic: *SAT Save and Restore

ACIS supports two kinds of save files, SAT and SAB, which stand for “Standard ACIS Text”

and “Standard ACIS Binary”, respectively. Although one is ASCII text and the other is binary

data, the model data information stored in the two formats is identical, so the term SAT file is

generally used to refer to either (when no distinction is needed).

SAT files are ASCII text files that may be viewed with a simple text editor. A SAT file

contains carriage returns, white space and other formatting that makes it readable to the

human eye. A SAT file has a

.sat file extension.

SAB files cannot be viewed with a simple text editor and are meant for compactness and not

for human readability. A SAB file has a

.sab file extension. A SAB file uses delimiters

between elements and binary tags, without additional formatting.

The binary formats supported are:

int 4–byte 2s complement (as long). . . . . . . . . . .

long 4–byte 2s complement. . . . . . . . . .

double 8–byte IEEE. . . . . . . .

char 1–byte ASCII. . . . . . . . . .

Getting Started Guide 8.0

 Summarization of logicals

 Summarization of enums

Indexing of IDs

This method of compression gives each ID an index, then allows that ID to be represented by

it’s index for the remainder of the sat file. For example, the first occurrence of ’loop’ in a sat

file would be represented by ”loop%1”. All subsequent occurrences of ’loop’ would be

represented by ”%1”.

Summarization of logicals

Some ACIS entities have sat–file data that has two–states, e.g., forward/reverse, out/in,

no_rotate/rotate, etc. In summary mode, these states are simply represented as the single

characters, T/F.

Summarization of enums

Some ACIS entities have sat–file data that has many states, e.g.,

non_singular/singular_low/singular_high/ singular_both, no_radius/single_radius/two_radii

etc. In summary mode, these states are simply represented by E0/E1/E2/E3 and so on.

Restoring in Summary Mode

Topic: SAT Save and Restore

It is not necessary to enable summary mode to restore a summarized sat file. The restore

mechanism automatically detects the presence of indexed id’s and loads the file as a

summarized sat file. Once ACIS determines that the sat file being restored is summarized, it

assumes that the entire file is fully summarized and loads it as such. As such, it is not

recommended that end users make modifications to summarized sat files.

In loading the summarized sat file, ACIS does not enable

save_summary_mode. Enabling

save_summary_mode can only be done through the option.

Compression Results

Topic: SAT Save and Restore

For sat files that are attribute heavy, summary mode can yield compressions of up to 40%. On

average, the compression is 10%.

Reserved Characters in SAT Files

Topic: *SAT Save and Restore

Several characters have special meaning when found in “unknown entity” string data in ACIS

SAT (

.sat) files. Therefore, these characters should not be contained in any user string data

written to SAT files. This includes string data in attributes, but applies to string data in any

unknown entities.

Getting Started Guide 8.0

Integer String length for the ACIS version string: “11”.. . . . . . .

String ACIS version which produced the file: “ACIS 7.0 NT”. This may be. . . . . . . .

different from the file version and can include the major release number, the

minor release number, and the point release number. It also includes the

platform on which it was produced.

Integer String length for the date string: “24”.. . . . . . .

String Date file produced (in C ctime format): “Mon Apr 09 16:44:18 2001”.. . . . . . . .

Double Number of millimeters represented by each unit in the model: “–1”.. . . . . . .

Real Value of resabs when the file was produced: “9.9999999999999995e–007”.. . . . . . . . .

Real Value of resnor when the file was produced: “1e–10”.. . . . . . . . .

Version Numbers

Topic: *SAT Save and Restore

Spatial has always maintained the concept of a current version (release) number in ACIS, as

well as a save version number. The save version allows one to create a SAT save file that can

be read by a previous version of ACIS.

Beginning with ACIS Release 4.0, the SAT save file format does not change with minor

releases, only with major releases. This allows applications that are based upon the same

major version of ACIS to exchange data without being concerned about the save version. To

provide this interoperability in a simple implementation, ACIS save files have contained a

symbol that accurately identified the major version number, but not the minor version. This

meant that applications created using the same major version of ACIS would produce

compatible save files, regardless of their minor versions. This was accomplished by simply

not incrementing the “internal” minor version number between major versions.

Beginning with Release 7.0, ACIS will again provide accurate major, minor, and point version

numbers, which can be queried using the functions

get_major_version, get_minor_version,

and

get_point_version. To summarize how release numbers and SAT changes are related:

 Major release: SAT file changes may be made; significant functionality changes likely;

may require significant changes to existing applications

 Minor release: No SAT file changes are made; may provide new functionality; may

require some minimal changes to existing applications

 Point release: Minor changes only (bug fixes)

Entity Records

Topic: *SAT Save and Restore

The header is followed by a sequence of entity records. Each entity record consists of a

sequence number (optional), an entity type identifier, the entity data, and a terminator.

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