Initial Graphics Exchange Specifications (.iges) import/export

Initial Graphics Exchange Specification (.iges) defines a vendor-neutral data format that allows the digital exchange of information.

Import

Import notes

• When Rhino reads an IGES file using the Open command, the Rhino units are set to those in the IGES file and the Rhino system tolerance is set to the IGES file tolerance, with some adjustments made to keep Rhino from setting a too small/big tolerance based on a bogus IGES file tolerance.
• When Rhino reads an IGES file using the Import command, the Rhino system tolerance is not changed. The tolerance used in rebuilding incorrect IGES trims is automatically computed and is always smaller than or equal to the Rhino system tolerance. If the IGES units do not match the Rhino units, you are given the option of scaling the imported IGES geometry so that it matches the current Rhino unit system.
• IGES supports only the printable subset of ASCII characters from character 32 to 127. This causes layer names to be truncated at the first occurrence of a non US character (like é).
• Unnecessary knots are removed from imported curves if the curve has identical geometry and parameterization.

Export

IGES Export Options

IGES type

Always use these settings. Do not show this dialog again.

IGES Export Detailed Options

IGES type

Specifies a pre-defined IGES type that attempts to match requirements in target software.

Edit Types

Click to customize existing IGES types or to create new IGES export types.

Author / Organization / Sender's product ID / Receiver's product ID

These are text fields in the IGES file that can be used for identification purposes.

IGES tolerance

In general, the IGES tolerance should match the absolute tolerance setting in Rhino, taking account the possible unit conversion.

The IGES tolerance does not affect the accuracy of the geometry.

IGES units

The units used for the IGES export.

Include Rhino notes in the IGES file

Check to save notes in IGES start section. Otherwise, the IGES start section is a blank line.

Use render color as IGES entity color

Check to use the render color of objects as the IGES entity color. Otherwise, Rhino uses the layer color of the object as the IGES entity color.

Always use these settings. Do not show this dialog again.

Export note

• Polygon meshes are not exported to IGES file.
• There are two types of solids modelers: surfaces and solids. Use the "surfaces" type when exporting a single surface to those products. Use the "solids" type when exporting anything you want to be able to join back together.

IGES Type Details

General

Name

Type a name for the IGES type.

See: Naming conventions in Rhino

IGES version

Choose between IGES version 5.2 and 5.3.

The difference is 5.2 stores years if you use two digits and 5.3 if you use four digits.

Text file type

Choose among MS-DOS, Unix, and MacOS style line endings.

Scale

Set the default scale factor for the IGES type. The number must be bigger than zero. In most cases, this number should be 1.

Points and Curves

Point Objects

Max degree

Composite curves as single B-spline

Curve made from two or more B-splines can be exported as an IGES 102 (composite curve) entity or as IGES 126 entities.

Use simple entities when possible

Use this setting to export NURBS curves that are lines, arcs, or circles (within the IGES tolerance) as IGES lines, IGES arcs, or IGES circles.

Fit rational curves

With this setting all rational curves (curve objects and trim curves) are approximated, in non-rational cubics, to the tolerance specified as the IGES tolerance.

Clamp end knots

With this setting periodic NURBS curves are exported as NURBS curves with clamped end knots.

Surfaces

Solids

Polysurfaces

Surfaces

Use simple entities when possible

With this setting NURBS surfaces that are planar (within the tolerance specified as the IGES tolerance) export as IGES planes or IGES trimmed planes.

Fit rational surfaces

With this setting, when possible, rational NURBS surfaces are be approximated with non-rational cubics to the tolerance specified as the IGES tolerance.

Clamp end knots

With this setting periodic NURBS surfaces are exported as NURBS surfaces with clamped end knots.

Split closed surfaces

If a surface is closed (like a cylinder), the surface will be split into two halves in the IGES file. If a surface is closed in both directions (like a torus), the surface will be split into four quarters in the IGES file.

Split bipolar surfaces

If a surface has poles at both ends (like a sphere), the surface is split so each half has just one pole.

IGES Export Types

IGES Type

Lists the currently defined IGES types.

New

Opens the IGES Type Details dialog box.

Copy Type

Opens the IGES Type Details dialog box with settings from the currently selected IGES type.

Edit

Opens the IGES Type Details dialog box to edit settings from the currently selected IGES type.

Delete

Deletes the currently selected IGES type.

The ReadEveryIGESEntity command imports all IGES entities, regardless of type.

The ReadEveryIGESEntity command only effects the next IGES file that is read. If you do something like:

open alpha.igs
ReadEveryIgesEntity
open beta.igs
open gamma.igs

Rhino attempts to read every entity only from beta.igs.

Rhino reads alpha.igs and gamma.igs normally, accepting only entities marked as geometry.

The IGESStudy command examines specific entities in an IGES file by limiting which portions of the IGES folder are parsed.

Background

Every entry into an IGES file also has folder entry (DE). The information that a DE stores determines if the corresponding IGES entity (curve, surface, solid, color, layer name, etc.) gets read. To further understand the importance of not blindly reading every entity in an IGES file as a top level piece of geometry, do this test:

Basic scenario:

You read an IGES file and it looks like some information is coming in damaged. The first thing you need to find out is the DE of the damaged objects. Run the IGESStudy command and turn the Label option on.

IGES debugging options (DEtest=Off FirstDE=1 LastDE=0 ReadEveryEntity=Off Label=On)

Read the file again. This time, every object you read has its Rhino name set to "DE N", where "N" is an odd number. The folder entries in an IGES file are labeled 1, 3, 5, 7, and so on. Select the bad objects and make a list of the DE's that are troublesome. Let us say 13, 137, and 9025 were coming in as bad objects.

Now you use the IGESStudy command to read just the problem entitles, one at a time.

IGES debugging options (DEtest=On FirstDE=13 LastDE=13 ReadEveryEntity=Off Label=On)

You verify that DE 13 is coming in as junk. Then, look at the IGES file (in a text editor or a program like IGESure) and see what DE 13 is supposed to be. If you understand the entity, you can use the IGESStudy command to read in the parts that are used to make the entity. For example, you can look at the base surface and trimming curves to see what might be going on. As you do this, you will find blocks of entities you need to read. In those cases, you can use the IGESStudy command to read chunks of the file. For example:

IGES debugging options (DEtest=On FirstDE=123 LastDE=199 ReadEveryEntity=On Label=On)

will read every entry with DE number between 123 and 199. If you only want to read top level entities you set ReadEveryEntity=Off.

The SetIGESLayerLevelMap command controls the correspondence between Rhino layers and IGES levels on IGES import and export from the command line or a script.

IGES "levels" are like Rhino layers, except they use a number as an identifier instead of a text name. If you have layer standards for products that use IGES to exchange data, you will need a way to define a correspondence between Rhino layer names and IGES level numbers. Rhino has a layer to level function.

Note

• In general, it is a good idea for Rhino's "Default" layer to correspond to IGES's level 0, but this is not required.
• This file can contain multiple flavors. A flavor has a name enclosed in square brackets [] followed by lines that look like:
  "<RhinoLayerName>" = N
  where N is a non-negative integer (0, 1, 2, 3, ... ).
  The Rhino layer name appears between the quotation marks.
  A flavor is terminated by a blank line.
  The converter/map program ignores spaces and tabs.
  The converter/map program ignores lines that begin with semi-colon (;).
  If an imported IGES file contains a level number that is not listed in the set of rules and does have a IGES level name, that level will automatically import to a layer called "IGES_LEVEL_N".
  If an exported Rhino layer name is not listed in the set of rules, an IGES level number is automatically selected.

See also

Import and export objects

Troubleshooting IGES Files with Rhinoceros

Wikipedia: IGES