What is inside an IGES file
IGES (Initial Graphics Exchange Specification) was first published in 1980 as a U.S. national standard for exchanging CAD geometry. STEP was later developed as its successor, yet old archives and some suppliers still send IGES. The unit is a flag in the global section of the file, and the viewer reads it.
Some IGES models are a set of separate surfaces rather than one closed solid. That explains most IGES trouble: two neighbouring patches can face opposite ways, and the mesh check then reports flipped triangles or inside-out normals.
How the IGS viewer opens surfaces
OpenCascade runs inside the tab and tessellates each surface. A 1 inch test cube declared in inches comes out at 25.4 mm, the same result as the STEP test. Precision has three levels, Coarse, Medium and Fine; a rounded cube gives 48, 84 and 172 triangles at those levels.
- Drop the .igs or .iges file on the page, or press Open File.
- Read X × Y × Z in the Info panel; switch Units mm/in if you think in inches.
- Look at the mesh check line to see whether the model is closed.
- Press Section or Measure to check a wall or a bore.
Flipped faces and other IGES problems
On a 6-surface test cube, the patches arrived with mixed orientation. Edit → Repair made the normals consistent and outward, and the message listed what it changed. Run it whenever the mesh check flags flipped triangles.
- Size looks wrong by 25.4. Compare the unit flag with what the sender meant. Units mm/in switches the display; Edit → Inches → mm rescales the mesh.
- Gaps between patches. Repair closes simple holes with a flat fan. A large curved gap needs a CAD fix at the source.
- Cut or booleans refuse to run. They need a watertight mesh, so run Repair first.
Inspecting an IGS part: views, sections, weight
Standard views put the part square to the screen: isometric, top, front, right and their opposites, in perspective or orthographic projection. Wireframe and the feature edges outline show where one surface patch ends and the next one begins.
The section plane runs along X, Y or Z with a slider and a flip button. The inside shows in red, so a thin wall or a missing face stands out. Once the model is closed, Info gives volume in cm³, surface area and weight for 17 materials, from aluminium to brass.
IGES next to STEP
When the sender can choose, ask for STEP. It stores exact solids, whole assemblies and the length unit. Open those files in the STEP viewer. For printing, IGES to STL saves the tessellated mesh in millimetres; that pair was converted and re-opened in tests. The 3D model viewer hub lists the other formats.
Questions and answers
How do I view an IGS file without CAD software?
Open this page in a Chromium browser and drop the .igs file. The surfaces are tessellated in the tab, so no install is needed.
Are .igs and .iges different formats?
No, they are two extensions for the same IGES format. The file picker here shows both.
Why does the mesh check report flipped triangles?
Some normals point inward, a common result when an IGES model is a set of loose surfaces. Edit → Repair turns them outward.
Can this IGES reader measure holes?
Measure snaps to vertices and shows the distance with ΔX, ΔY and ΔZ. On a bore, pick two opposite vertices at Fine precision.
Do I have to wait for the engine every time?
No. The 7.6 MB engine downloads with your first STEP or IGES file, and the next files open without that download.
Does my file leave the computer?
No. OpenCascade is served from our domain and runs in the tab. In a full test run the page made 0 requests to other domains and posted nothing.