# IfcPolygonalFaceSet and face winding.

**URL:** <https://forums.buildingsmart.org/t/ifcpolygonalfaceset-and-face-winding/3169>\
**Category:** Developers\
**Tags:** ifc4\
**Created:** [December 2, 2020, 2:23pm UTC](https://forums.buildingsmart.org/t/ifcpolygonalfaceset-and-face-winding/3169 "2020-12-02T14:23:24Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![claimred](https://avatars.discourse-cdn.com/v4/letter/c/e47c2d/32.png) [@claimred](https://forums.buildingsmart.org/u/claimred)\
**Post date:** [December 2, 2020, 6:04pm UTC](https://forums.buildingsmart.org/t/ifcpolygonalfaceset-and-face-winding/3169/2 "2020-12-02T18:04:04Z")

</div>

The bottom face seems to be mentioned twice (1, 2, 3, 4) & (1, 4, 3, 2) (which contradicts the informal proposition about unique faces). And “front” face is not found. 🤔

Guess it should be

```diff
-#1 IfcIndexedPolygonalFace: ((1, 2, 3, 4)
+#1 IfcIndexedPolygonalFace: ((1, 2, 6, 5)
#2 IfcIndexedPolygonalFace: ((6, 2, 3, 7)
#3 IfcIndexedPolygonalFace: ((7, 3, 4, 8)
#4 IfcIndexedPolygonalFace: ((8, 4, 1, 5)
#5 IfcIndexedPolygonalFace: ((1, 4, 3, 2)
#6 IfcIndexedPolygonalFace: ((6, 7, 8, 5)

```

 ![image](https://us1.discourse-cdn.com/flex016/uploads/buildingsmart1/original/2X/7/7a2b0b70c6aee4ef00d57104f46404608f8b1d0c.png)

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