IGES Translation Notes
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IGES is the "Initial Graphics Exchange Specification",
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
NASA Support Operations - MSFC
INTERGRAPH Huntsville, AL
Conversion of an active EMS file to IGES (using MSFC custom
- Turn all layers ON in all views, turn 'Element Display' and
'Element Locate' ON for all elements, and fit all views.
- Delete all elements not to be translated.
- Select the directory in which to place the resulting IGES
- Select a flavor and enter the desired Chord Height Tolerance.
- Prepare the active file for conversion using the 'Prepare
Active EMS File' button (remember not to save when exiting EMS).
- 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).
- 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).
- View the log file using the 'View Log File in Form' button.
- 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.
- 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).
- Disable the translation of 'invisible entities' and select
only the desired entities to be translated.
- 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:
- The 'STOP' button may be used to abort if an error occurs
when networking with the remote server.
- 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.
- Set the Chord Height Tolerance' equal to that of the model
file (usually 0.001).
- Elements with display OFF and elements on layers that have
been turned OFF are translated.
- Elements that are ineligible for selection are not
translated. Use 'Locate Eligibility' and 'Change Layer Locate
Eligibility" to change the status of these elements.
- If problems occur with derived surfaces and solids created
from b-spline curves (revolutions, projections, etc.), try
splitting the surfaces at the cusps.
- 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.
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