IGES Translation Notes

Return to NASA STEP Central
IGES is the "Initial Graphics Exchange Specification", ANSI/ASME Y14.26M-1989.

Note: STEP (ISO 10303) is a demonstrably superior technology to IGES, so the use of STEP instead of IGES is strongly encouraged for all new data exchange applications. However, these notes are provided for those who may have legacy IGES data or who may not yet have acquired a STEP translator for their software application but have an IGES translator.

IGES Tips (Lessons Learned)

IGES is not an exact science. It often requires much "tweaking" on a per file basis while drawing on past experiences. This document is a collection of "Lessons Learned" related to the conversion and flavoring of IGES files.


Brent A. Newsom
Mechanical Engineer
NASA Support Operations - MSFC
(205) 544-6656

EMS Files

Conversion of an active EMS file to IGES (using MSFC custom interface):

  1. Turn all layers ON in all views, turn 'Element Display' and 'Element Locate' ON for all elements, and fit all views.
  2. Delete all elements not to be translated.
  3. Select the directory in which to place the resulting IGES file.
  4. Select a flavor and enter the desired Chord Height Tolerance.
  5. Prepare the active file for conversion using the 'Prepare Active EMS File' button (remember not to save when exiting EMS).
  6. Save the prepared file under a new name using the 'Save Active EMS File' button (the saved file will be placed in the directory shown in the form. EMS, IGES, and log file information will be filled in automatically).
  7. Submit the EMS file for conversion using the 'Submit EMS File in Form' button (the IGES file will be placed in the directory shown in the form).
  8. View the log file using the 'View Log File in Form' button.
  9. View the IGES file using the 'View IGES File in Form' button (this will automatically bring up IGESVIEW which is a third party IGES viewer by IGES Data Analysis, Inc.).

Note: Non-active EMS files can be converted to IGES by filling in the directory, EMS, IGES, and log file information in the form and then pressing the Submit button. A non-active EMS file cannot be 'prepared'.


Note: The P3/PATRAN flavor button uses the 'Surface', 'NURB Curve as Polynomial Curve', and 'All Surfaces as NURBs' options.
  1. Toggle the 'NURBs Accelerator' OFF (The NURBs Accelerator by default causes curve and surface geometry to be converted to a piecewise polynomial format. Although this option provides an increase in display performance, problems may occur when importing IGES files).
  2. Disable the translation of 'invisible entities' and select only the desired entities to be translated.
  3. Decrease 'global' tolerance if gaps are present between surfaces after conversion.


Note: The RASNA flavor button uses the 'Surface' option.


Note: Watch for tolerance problems. PTC modeling tolerance by default is two orders of magnitude looser than EMS bastol.



Output IGES file from IDEAS using the trimmed curve option only. It is important to address tolerance issues before modeling in IDEAS. By default, the IDEAS modeling tolerance is set to 0.01 mm or 3.94E-4 in. EMS by default is much tighter at 1E-6 in.

Comments specific to EMS to IGES conversions:

  1. The 'STOP' button may be used to abort if an error occurs when networking with the remote server.
  2. When the conversion script is running, each step in the process is echoed to the window from which EMS was invoked. It is helpful if this window is visible before bringing up the form.
  3. Set the Chord Height Tolerance' equal to that of the model file (usually 0.001).
  4. Elements with display OFF and elements on layers that have been turned OFF are translated.
  5. Elements that are ineligible for selection are not translated. Use 'Locate Eligibility' and 'Change Layer Locate Eligibility" to change the status of these elements.
  6. If problems occur with derived surfaces and solids created from b-spline curves (revolutions, projections, etc.), try splitting the surfaces at the cusps.
  7. When placing skins, surfaces by boundaries, and other complex surfaces, break up into smaller sections. For example, it may not always be best to use one complex skinning cross section when it can be represented by several simpler sections.

Webmaster: Steve Waterbury (email: stephen.c.waterbury@nasa.gov)

Responsible NASA Contact:
Stephen Waterbury
NASA Product Data Exchange Working Group

NASA Logo NASA WWW Home Page