How to rotate image with negative values

I am using the below code in server side to rotate my images ,it works fine for the angle like 5,10,20..360. In the same project I have to rotate images whose angle are already saved in database from Java application. It contains values like -1,-1.23,1.4543545 etc. and its not rotating with my below function.

UPDATED/WORKING CODE

 public static Bitmap rotateCenter(string imagepath,Bitmap bmpSrc, float theta)
{
    Unit Width = 0;
    Unit Height = 0;

    if (imagepath.Contains("Images\\streets"))
    {
       if (imagepath.Contains("streets\\circle-4-way.png") || imagepath.Contains("streets\\circle_street.png"))
        {
            Width = Unit.Pixel(220);
            Height = Unit.Pixel(220);
            theta = theta + 10;
        }
     }
    else
    {
        Width = Unit.Pixel(50);
        Height = Unit.Pixel(30);

    }
    Double newdeg = theta * (180.0 / Math.PI);
    theta = (float)newdeg;

    Matrix mRotate = new Matrix();
    mRotate.Translate(Convert.ToInt32(Width.Value) / -2, Convert.ToInt32(Height.Value) /开发者_JAVA技巧 -2, MatrixOrder.Append);
    mRotate.RotateAt(theta, new Point(0, 0), MatrixOrder.Append);

    using (GraphicsPath gp = new GraphicsPath())
    {  // transform image points by rotation matrix
        gp.AddPolygon(new Point[] { new Point(0, 0), new Point(Convert.ToInt32(Width.Value), 0), new Point(0, Convert.ToInt32(Height.Value)) });
        gp.Transform(mRotate);
        PointF[] pts = gp.PathPoints;

        // create destination bitmap sized to contain rotated source image
        Rectangle bbox = boundingBox(bmpSrc, mRotate);
        Bitmap bmpDest = new Bitmap(bbox.Width, bbox.Height);


        using (Graphics gDest = Graphics.FromImage(bmpDest))
        {  // draw source into dest


            Matrix mDest = new Matrix();
            mDest.Translate(bmpDest.Width / 2, bmpDest.Height / 2, MatrixOrder.Append);
            gDest.Transform = mDest;
            gDest.DrawImage(bmpSrc, pts);
            gDest.DrawRectangle(Pens.Transparent, bbox);
            //drawAxes(gDest, Color.Red, 0, 0, 1, 100, "");
            return bmpDest;
        }
    }
}

It looks like the negative values are in radians. First convert to degrees: DEGREES = RADIANS * (180/pi);

Then add 360 to the result, that should give you a positive angle.

Feed that to your method.