Rotate camera around any axis any angle

By Adam Nagy

This is a generalization of this post: 
http://adndevblog.typepad.com/manufacturing/2014/11/rotate-drawing-view-around-x-axis-of-sheet.html

Here we'll use the Matrix class to help us create a matrix that can transform any point or vector around any vector/axis and an angle: Matrix.SetToRotation(Angle As Double, Axis As Vector, Center As Point) 

To make sure we have a precise radian value for 90 degrees I'm using 2 * Atn(1) inside VBA. In languages like .NET there is a constant for PI, so you could use that instead.

We just need to get the vector we want to rotate around inside the Model space. If the vector we want to use is in the Sheet space then we need to transform it using SheetToModelTransform matrix. 

Once we have both the rotation centre (Camera.Target in our case) and the rotation axis (Sheet X inside the model space in our case) then we can create the transformation matrix and use it to get the new Eye position and UpVector direction.

Sub RotateBaseView()
  Dim baseView As DrawingView
  Set baseView = ThisApplication.ActiveDocument.SelectSet(1)
  
  Dim tr As TransientGeometry
  Set tr = ThisApplication.TransientGeometry
  
  Dim c As Camera
  Set c = baseView.Camera
  
  Dim oldEye As Point
  Set oldEye = c.eye.Copy
  
  Dim oldTarget As Point
  Set oldTarget = c.Target.Copy
  
  Dim oldUpVector As UnitVector
  Set oldUpVector = c.UpVector.Copy
  
  ' Get the Sheet's X axis into the model space
  Dim sheetXInModel As Vector
  Set sheetXInModel = tr.CreateVector(1, 0, 0)
  Call sheetXInModel.TransformBy(baseView.SheetToModelTransform)
  
  ' Calculate rotation in the model
  ' around the Target and the Sheet X
  ' in model space
  Dim m As Matrix
  Set m = tr.CreateMatrix()
  
  ' Set the rotation angle to 90 degrees
  ' Atn(1) = 45 degrees in radian
  Dim Rad90 As Double
  Rad90 = 2 * Math.Atn(1)
  Call m.SetToRotation(Rad90, sheetXInModel, oldTarget)

  ' Now we just have to transform the points and
  ' vectors
  Call oldEye.TransformBy(m)
  c.eye = oldEye
  Call oldUpVector.TransformBy(m)
  c.UpVector = oldUpVector
  
  Call c.ApplyWithoutTransition
End Sub