DATA EXCHANGE FORMAT IGES A presentation by Mahesh Babu Gajula (206516) Data Management for Engineering Applications

Overview Data Exchange in IGES History File structure IGES File – Samples IGES Entities Structure – Start – Global – Data Entry – Parameter Data – Terminate Advantages Disadvantages References

Data Exchange in IGES IGES stands for International (originally ‘Initial’) Graphics Exchange Standards and a neutral data format that allows the digital exchange of information among CAD systems. Figure 1. Data exchange using neutral file

Data Exchange in IGES(Contd.) When this neutral file is used, each CAD system needs only one pre-processor and one postprocessor which form one set of translators. Figure 2 illustrates the way the pre-processor imports the data into the system and the post- processor outputs the file into standard. Number of two-way translators needed for n CAD systems to exchange data among them. N=c(n/2)=n!/2!(n-2)!

Data Exchange in IGES(Contd.) CAD IGES Post Processor Pre Processor Post Processor Figure 2. CAD data exchange

History The Initial Graphics Exchange Specification (IGES) (pronounced eye-jess) is a file format which defines a vendor neutral data format that allows the digital exchange of information among computer aided design (CAD) systems. First developed by National Institute of Standards and Technology (NIST) in 1980.

History(Contd.) IGES version 1.0 was developed in January 1980 mean for two dimensional and three dimensional mechanical drawings. Then adopted by the American National Standards Institute (ANSI) in 1981 year,which it is used for communicating product definition data.

IGES MODEL DRAWINGS Skull modelIGES model of a car

FILE STRUCTURE Global section Directory entry section (DE) Parameter data section(PD) Terminate section Start section All geometric entries are given here 2)Table 2 specifications of the IGES file

FILE STRUCTURE(Contd.) The file is divided into 5 sections: Start-S Global-G Directory Entry-D Parameter Data-P Terminate-T The above characters are listed in Column 73. Characteristics and geometric information for an entity is split between two sections; – Two record, fixed-length format (the Directory Entry, or DE Section). – Multiple record, comma delimited format (the Parameter Data, or PD Section).

IGES FILE

Output of Above file When displayed, the user should see: 2 Yellow points. – (Hard to see on a white background, but most CAD systems use a black background). 2 Red circular arcs 2 Green lines.

Output of Above file(Contd.) The above drawing contains only two POINTS (Type 116), two CIRCULAR ARC (Type 100), and two LINE (Type 110) entities. It represents a slot, with the points at the centres of the two half-circles that form the ends of the slot, and the two lines that form the sides.

IGES entities specification Table1 : List of Entities

Start section Human readable introduction to the file. Described as a “prologue” to the IGES file. Characters used as delimiters between individual entries and between records (usually commas and semicolons respectively), The name of the IGES file itself, Vendor and software version of sending (source) system, Number of significant digits in the representation of integers and single and double precision floating point numbers on the sending systems, Date and time of file generation, Model space scale, Model units, Minimum resolution and maximum coordinate values, Name of the author of IGES file. Global Section

List of all entities in IGES file with certain attributes with them. The entry for each entity occupies two 80-character records. – Divided into a total of twenty 8-character fields. The first and eleventh(beginning of the second record of any given entity) fields contains the entity type number – Such as 100 for circle,110 for line etc. The second field contains a pointer to the parameter data entry for the entity in the PD section. Directory Entry Section

Parameter data section Contains the actual data defining each entity listed in the DE section. Each entity has always two records in the DE section. The number of records required for each entity varies from one entity to another – (the minimum is one record) and depends on the amount of data. Parameter data are placed in free format in columns 1 through 64.

Parameter data section(Contd.) The parameter delimiter (usually a comma). – To separate parameters The record delimiter (usually a semicolon). – To terminate the list of parameters. Both delimiters are specified in the Global section of the IGES file. Column 65 is left blank. Columns 66 through 72 on all PD records contain the entity pointer specified in the first record of the entity in the DE section.

Terminate Section The Terminate section contains a single record that specifies the number of records in each of the four preceding sections for checking purposes.

Advantages of IGES Product data exchange among different CAD/CAM systems are even animation and documentation software are of great importance to computer – integrated manufacturing(CIM). The sharing of data is also key successful development to he concurrent engineering. IGES also educes lead time of product development. Due to the large variety of CAD systems in the market,design data exchange among different CAD systems is indispensable.

Disadvantages of IGES IGES file does not have a formal information model. Problems occur during file exchanges and manipulations. Hard to understand file formats. IGES does not support life cycle information which may be relevant for engineering applications other than design.

References 1) _13. 2) _6. 3) m/version6.pdf. 4) 5) 6) guides/mergedProjects/Opening_Models/IGE S_Entities_Supported.htm.

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