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Initial Graphics Exchange Specification (IGES)

IGES or Initial Graphics Exchange Specification is an exchange file format for CAD originally published in January 1980 by United States National Bureau of Standards. IGES file format became widely adopted by commercial and government entities. Many older specifications are stored in IGES format to make sure that data could be read even if original software which was used to create CAD model is no longer available.

IGES is an ASCII text file format with each line exactly 80 characters long (this line length is an artefact from a time when computers typically displayed 80 columns of visible text). IGES file is split into 5 sections:

  • Start (S)
  • Global (G)
  • Directory Entry (D)
  • Parameter Data (P)
  • Terminate (T)

Start and Global sections typically contain information about the name of the file and its source.

Each entity in directory entry (D) section is represented by two lines with the following data in it:

Line 1:

  • Entity Type – numeric code of entity type
  • PD pointer – pointer to a parameter section with actual entity data
  • Structure
  • Line Font Pattern – defines if line should be solid, dashed, dotted, etc.
  • Level – levels associated with an entity
  • View – view associated with an object
  • Transformation matrix pointer – pointer to a transformation matrix or zero if no transformation
  • Label Display Associativity – defines how the entity label appears
  • Status Number – flags associated with an entity
  • Section Code and Sequence Number – line number within the data directory section

Line 2:

  • Entity Type - numeric code of entity type
  • Line Weight Number – line thickness for the entity
  • Color Number – entity color
  • Parameter Line Count – number of lines which entity uses in parameter data section
  • Form Number – defines form or representation of the entity.
  • Reserved
  • Reserved
  • Entity Label – identifier specified by an application
  • Entity Subscript Number – numeric identifier for the entity. Together with “Entity Label” form unique identifier for the entity
  • Section Code and Sequence Number – line number within the data directory section

Parameter data sections follows Directory Entry section and lists all data associated to each entity.

Below is an example of an IGES file:
SolidWorks IGES file using analytic representation for surfaces S 1
1H,,1H;,10HP65.SLDPRT,45HI:\Example.IGS, G 1
15HSolidWorks 2011,15HSolidWorks 2011,32,308,15,308,15,10HP65.SLDPRT, G 2
1.,2,2HMM,50,0.125,13H120402.093950,1E-008,499990.,8H,,11,0,13H1G 3
20402.093950; G 4
314 1 0 0 0 00000200D 1
314 0 8 1 0 0D 2
110 2 0 0 0 01010000D 3
110 0 0 1 0 0D 4
110 3 0 0 0 01010000D 5
110 0 0 1 0 0D 6
314,75.2941176470588,75.2941176470588,75.2941176470588,; 1P 1
110,0.,0.,-1011.6,0.,0.,-11.6; 3P 2
110,25.2,0.,-11.8,25.4,0.,-11.6; 5P 3

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Extension Details
AutoCAD Drawing File Format
MIME Type
  • application/acad
  • application/x-acad
  • application/autocad_dwg
  • image/x-dwg
  • application/dwg
  • application/x-dwg
  • application/x-autocad
  • image/vnd.dwg
  • drawing/dwg
Opens with
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  • DWG TrueView
  • Autodesk Online Viewer