face issue and more ...

[Ning_Zhou]

assume all faces / curves are coplanar:

1) is there a way to do face boolean operation like join all planar faces together?

2) is there a way to create extrusion from face?

3) is there a way to check if curve is inside face? looks like Face.Intersect will treat all coplanar curves as SetComparisonResult.Subset, i'm currently using Face.IsInside which is not efficient.

thanks.

[mikako_harada]

1) is there a way to do face boolean operation like join all planar faces together?

How about the following method? 

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Face.Intersect Method (Face)

Calculates the intersection of the specified face with this face and returns the intersection results.

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2) is there a way to create extrusion from face?

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FamilyItemFactory.NewExtrusion Method 

Add a new Extrusion instance into the Autodesk Revit family document.

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you can defind profile from a face. 

3) is there a way to check if curve is inside face? looks like Face.Intersect will treat all coplanar curves as SetComparisonResult.Subset, i'm currently using Face.IsInside which is not efficient.

Looks like you already tried.  But I would try below and some combinations. 

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Face.Intersect Method (Face)

Calculates the intersection of the specified face with this face and returns the intersection results.

Face..::..Intersect Method (Curve)

Calculates the intersection of the specified curve with this face.

Face.IsInside Method (UV)

Indicates whether the specified point is within this face.

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[Ning_Zhou]

thanks Mikako.

since all faces / curves are coplanar, Face.Intersect won't work, besides, what i need is basically the 2D face boolean operation.

you can create extrusion based on simple profile, but not relatively complicated profile, until factory can make available of sketch-mode editing which will solve lots of issues!