RasterImage Inverse Transform

By Balaji Ramamoorthy

A BlockReference provides the “BlockTransform” matrix which can be helpful in case you need to transform the entity to negate the effects of displacement, rotation and scaling. A RasterImage entity does not provide a similar matrix, but can be constructed knowing the individual rotation, displacement and scale values in x and y directions. Here is a sample code to negate the scaling, displacement and rotation of a selected raster image.

[CommandMethod("RITest")]
public void RITestMethod()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed 
        = Application.DocumentManager.MdiActiveDocument.Editor;
 
    PromptEntityOptions opts 
            = new PromptEntityOptions("Pick a raster image : ");
    opts.SetRejectMessage("Must select a raster image");
    opts.AddAllowedClass
          (
            typeof(Autodesk.AutoCAD.DatabaseServices.RasterImage),
            false
          );
 
    PromptEntityResult res = ed.GetEntity(opts);
    if (res.Status != PromptStatus.OK)
        return;
 
    using (Transaction tr = db.TransactionManager.StartTransaction())
    {
        RasterImage ri = tr.GetObject(
                                        res.ObjectId, 
                                        OpenMode.ForWrite
                                     ) as RasterImage;
 
        Matrix3d invTransform = Matrix3d.Identity;
 
        invTransform = invTransform.PreMultiplyBy
                (
                    Matrix3d.Rotation(  -ri.Rotation, 
                                        Vector3d.ZAxis, 
                                        ri.Orientation.Origin)
                );
 
        invTransform = invTransform.PreMultiplyBy
                (
                    Matrix3d.Displacement(  
                    Point3d.Origin - ri.Orientation.Origin)
                );
 
        Vector2d riScale = ri.Scale;
        double scaleX = riScale.X;
        double scaleY = riScale.Y;
 
        double[] coeffs = new double[]
        {
            scaleX, 0, 0, 0,
            0, scaleY, 0, 0,
            0, 0, 1, 0,
            0, 0, 0, 1
        };
 
        Matrix3d scaleMatrix = new Matrix3d(coeffs);
        invTransform = invTransform.PreMultiplyBy
                                    (scaleMatrix.Inverse());
 
        ri.TransformBy(invTransform);
 
        // If you need the transformation matrix and not its inverse, 
        // simply invert the matrix again.
        // Matrix3d riTransform = invTransform.Inverse();
 
        tr.Commit();
    }