How to orient the view normal to a plane defined by 3 points and then zoom to fit.

I think this might be of assistance.

Camera Transformation and View Matrix

This was the code we used in the end. ( All helper extension methods can be found at GitHub - Weingartner/SolidworksAddinFramework))

using SolidworksAddinFramework;

using SolidWorks.Interop.sldworks;

namespace WeinCadSW.Macros.ToolAligner

{

    /// <summary>

    /// Provides the orientation matrix for IModelView::Orientation3. If you

    /// have 3 points that define a plane and you wish to look at the center

    /// of those three points in a direction normal to the plane then

    /// use this.

    /// </summary>

    public class ViewOrientationFor3Points

    {

        public MathPoint P0 { get; set; }

        public MathPoint P1 { get; set; }

        public MathPoint P2 { get; set; }

        /// <summary>

        /// The center of the three points

        /// </summary>

        public MathPoint PCenter { get; }

        /// <summary>

        /// The normal to the plane defined by the three points

        /// </summary>

        public MathVector Normal { get; }

        /// <summary>

        /// Orientation matrix for IModelView::Orientation3

        /// </summary>

        public MathTransform Orientation { get; set; }

        public ViewOrientationFor3Points(IMathUtility math, double[] p0, double[] p1, double[] p2)

        {

            P0 = math.Point(p0);

            P1 = math.Point(p1);

            P2 = math.Point(p2);

            var pTool = p0;

            var pCurve = p1;

            var pAxis = p2;

            var va = math.Vector(pTool, pCurve).Normalise();

            var vb = math.Vector(pTool, pAxis).Normalise();

            var w = ((MathVector)va.Cross(vb)).Normalise();

            var u = math.Vector(new[] {1.0, 0, 0}).CrossTs(w);

            var v = w.CrossTs(u);

            var c = math.Vector(new[] { pTool, pCurve, pAxis }.Average());

            var trans = math.ComposeTransform(u, v, w, c, 1);

            Orientation = (MathTransform)trans.Inverse();

            Normal = w;

            PCenter = math.Point(new[] {p0, p1, p2}.Average());

        }

    }

}