topic Re: Face Lower Left corner in Revit API Forum

Face Lower Left corner

LandformX — Wed, 24 Mar 2021 09:38:50 GMT

Hi Guys,

It's me again 😉 wondering why I'm getting different result on getting face bounding box max/min as shown in the video.

PlanarFace face = solid.Faces.get_Item(0) as PlanarFace; BoundingBoxUV bbUV = face.GetBoundingBox(); XYZ p3 = face.Evaluate(bbUV.Max); FamilyInstance famInst = doc.Create.NewFamilyInstance(p3, fixture, Autodesk.Revit.DB.Structure.StructuralType.NonStructural);

Thanks again.

Re: Face Lower Left corner

RPTHOMAS108 — Wed, 24 Mar 2021 12:07:11 GMT

Can't easily see what you are doing from that gif but I'm assuming face 0 isn't always the same face direction. Have you compared the normal vectors of each?

Face.getBoundingBox:

"A BoundingBoxUV with the extents of the parameterization of the face."

Re: Face Lower Left corner

LandformX — Wed, 24 Mar 2021 12:39:52 GMT

Hi @RPTHOMAS108 thank you again for your quick response, basically I just want to get lower left corner for each face, so I thought I'll start by getting bb min, I haven't compare their vectors yet (and not sure how) since they are all rectangular i just thought they should be returning at least same corner locations?

Re: Face Lower Left corner

LandformX — Wed, 24 Mar 2021 12:43:04 GMT

PS. I did face normal comparison and they are all the same

Re: Face Lower Left corner

RPTHOMAS108 — Wed, 24 Mar 2021 16:21:27 GMT

Since you are dealing with a PlanarFace it has an X,Y and Z direction.

It will help your understanding to plot these and what that means for BoundingBoxUV coords plotted in that space. You can use Face.Evaluate to get XYZ for a given UV point on a face, whilst Face.ComputeDerivative will give you the direction vectors at a given point (for PlanarFace they don't change).

In the below RGB represents X,Y,Z at face origin respectively. Green line drawing from min to max (after transforming into coordinate space of face).

Ordinarily the UV points aren't as useful as say projecting an XYZ of a known location onto a face (Face.Project). If you are tiling the face etc. then UV may be useful but you have to consider direction and form of parameters may not be as you expect.

Re: Face Lower Left corner

LandformX — Thu, 25 Mar 2021 08:24:36 GMT

Thanks @RPTHOMAS108 , very helpful, I found an answer from @jeremy_tammik 's utility samples, again thank you for both of you.

if anyone will need the same i posted jeremy's code below. Cheers!

// <summary> /// Return the bottom four XYZ corners of the given /// bounding box in the XY plane at the given /// Z elevation in the order lower left, lower /// right, upper right, upper left: /// </summary> public static XYZ[] GetBottomCorners( BoundingBoxXYZ b, double z ) { return new XYZ[] { new XYZ( b.Min.X, b.Min.Y, z ), new XYZ( b.Max.X, b.Min.Y, z ), new XYZ( b.Max.X, b.Max.Y, z ), new XYZ( b.Min.X, b.Max.Y, z ) }; } /// <summary> /// Return the bottom four XYZ corners of the given /// bounding box in the XY plane at the bb minimum /// Z elevation in the order lower left, lower /// right, upper right, upper left: /// </summary> public static XYZ[] GetBottomCorners( BoundingBoxXYZ b ) { return GetBottomCorners( b, b.Min.Z ); }