Rotating Breps in VB.net

Hi everyone,

I am wondering how to select the origin point on which a Brep is rotated in VB.net? The Breps I have created are just boxes and i would like to be able to rotate them on the y axis from the centre of the bottom surface.

I have had a look on the Grasshopper Primer V2 and found the code "rotate.Rotation(angle, OnUtil.On_yaxis, OnUtil.On_origin)" but I don't know how to change the OnUtil.On_origin to the centre point of the base surface.

Any help would be very much appreciated.

Replies to This Discussion

Permalink Reply by Dirk Anderson on December 8, 2009 at 12:31am

you need to determine which is the bottom surface and then use a centroid of the brep.Face().NurbsSurface as an origin point. See code below of how to extrapolate the surface and centroid.

Private Sub RunScript(ByVal inContext As List(Of OnBrep), ByRef A As Object, ByRef B As Object)
Dim srfList As New List (Of OnNurbsSurface)
Dim ptList As New List (Of On3dPoint)
For i As Int32 = 0 To inContext.Count() - 1
Dim brep As New OnBrep
brep = inContext(i)
Dim faceCount As Int32 = brep.m_F.m_count
For j As Int32 = 0 To faceCount - 1
Dim nSrf As New OnNurbsSurface
nSrf = brep.Face(j).NurbsSurface
Dim mp As New OnMassProperties
nSrf.AreaMassProperties(mp)
Dim pt As New On3dPoint(mp.Centroid)
ptList.Add(pt)
srfList.Add(nSrf)
Next
Next

A = ptList

End Sub

Permalink Reply by Axiom on December 16, 2009 at 10:09am

Hi Dirk,

Thanks for getting back to me. I had managed to find a bit of a work around but it involved me doing a lot more manual calculations. I will try this code as soon as I get a free moment.

Thanks again

Permalink Reply by David Rutten on December 16, 2009 at 11:15am

Hi Axiom,

OnBreps have a Rotate method as well as a Transform method. If you can get away with using one of the overloads of OnBRep.Rotate() I suggest you follow that route.

In either case, rotation origins are just regular points, and rotation axes are regular vectors. Thus, to set a custom rotation point do something like:

New On3dPoint(x,y,z)

and for custom rotation axes do something like:

New On3dVector(x,y,z)

--
David Rutten
david@mcneel.com
Poprad, Slovakia

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