c++ - 测试二维变换矩阵是否正交

Question

我们发现 HP 的打印机驱动程序无法为其许多打印机正确处理 PlgBlt()。

我们的目的是自己处理任何正交旋转，并且只让打印机处理缩放和平移(它似乎可以正确处理)。

在我即将“绘制”位图到打印机的 DC 的代码点，我有一个二维矩阵可供使用。

我的数学很弱，但我对矩阵数学的了解足以使用它们来转换 2D 或 3D 坐标。但基础数学对我来说是不透明的。

因此，我需要检测给定的二维矩阵在其变换中是否正交(无论如何旋转方面)。我想问这个问题的另一种方法是:如何从 2D 矩阵中获取旋转 vector ？如果我知道以弧度或度数表示的旋转角度，我可以说它是否正交 (0,90,180,270)。

据推测，代码在这个主题上是通用的，但下面是我们使用的代码的基础知识，以防有帮助:

typedef double ThreeByThreeMatrix[3][3];    // 3x3 for an X, Y coordinate transformation matrix

然后有一个处理最明显操作的包装器:

class Simple2DTransform
{
public:

    ////////////////////////////////////////////////////
    // Construction
    ////////////////////////////////////////////////////

    // we always begin life as an identity matrix (you can then apply scale, skew, etc.)
    Simple2DTransform() 
    {
        Reset(); 
    }

    ////////////////////////////////////////////////////
    // Operators
    ////////////////////////////////////////////////////

    bool operator == (const Simple2DTransform & rhs) const
    {
        return memcmp(m_matrix, rhs.m_matrix, sizeof(m_matrix)) == 0;
    }

    Simple2DTransform & operator *= (const Simple2DTransform & rhs)
    {
        return *this = GetCrossProduct(rhs);
    }

    ////////////////////////////////////////////////////
    // Setup
    ////////////////////////////////////////////////////

    // reset to the identity matrix
    Simple2DTransform & Reset()
    {
        memcpy(m_matrix, GetIdentityMatrix(), sizeof(m_matrix)); 
        return *this;
    }

    // combine with the specified translation
    Simple2DTransform & Translate(double x_shift, double y_shift)
    {
        Simple2DTransform transform;
        translate(x_shift, y_shift, transform.m_matrix);
        return *this *= transform;
    }

    // combine with the specified operations (these are cumulative operations, so rotating twice by 1 degree gives a total of 2 degrees rotation)
    Simple2DTransform & Rotate(double radians)
    {
        Simple2DTransform transform;
        rotate(radians, transform.m_matrix);
        return *this *= transform;
    }

    // apply a heterogeneous scale factor
    Simple2DTransform & Scale(double x_scale, double y_scale)
    {
        Simple2DTransform transform;
        scale(x_scale, y_scale, transform.m_matrix);
        return *this *= transform;
    }

    // apply a homogeneous scale factor
    Simple2DTransform & Scale(double scale) 
    {
        return Scale(scale, scale); 
    }

    // apply a skew
    Simple2DTransform & Skew(double skew)
    {
        Simple2DTransform transform;
        skew_y(skew, transform.m_matrix);
        return *this *= transform;
    }

    ////////////////////////////////////////////////////
    // Queries
    ////////////////////////////////////////////////////

    // return the cross product of this and the given matrix
    Simple2DTransform GetCrossProduct(const Simple2DTransform & rhs) const
    {
        Simple2DTransform result;
        GEMM(m_matrix, rhs.m_matrix, result.m_matrix);
        return result;
    }

    // returns the inverse of ourselves
    Simple2DTransform GetInverse() const
    {
        // note: invert mucks with both matrices, so we use a copy of ourselves for it
        Simple2DTransform original(*this), inverse;
        invert(original.m_matrix, inverse.m_matrix);
        return inverse;
    }

    // derivative values
    double GetCoefficient(int i, int j) const
    {
        return m_matrix[i][j];
    }

    // return the cross product
    double GetDeterminate() const
    {
        return m_matrix[0][0]*m_matrix[1][1] - m_matrix[0][1]*m_matrix[1][0];
    }

    // returns the square root of the determinate (this ignores heterogeneous scaling factors)
    double GetScale() const
    {
        return sqrt(abs(GetDeterminate()));
    }

    // returns true if there is a scale factor
    bool IsStretched() const
    {
        return (abs(abs(m_matrix[0][0]) - abs(m_matrix[1][1])) > 1.0e-7
             || abs(abs(m_matrix[0][1]) - abs(m_matrix[1][0])) > 1.0e-7);
    }

    // true if we're the identity matrix
    bool IsIdentity() const
    {
        return memcmp(m_matrix, GetIdentityMatrix(), sizeof(m_matrix)) == 0;
    }

    // returns true if this represents the same transformation as the given subtable
    bool IsSubtableEqual(const SUBTABLE * pSubTable) const
    {
        ASSERT(pSubTable);
        if (abs(pSubTable->tran1 - m_matrix[0][0]) > 1.0e-7)
            return false;
        if (abs(pSubTable->tran2 - m_matrix[1][0]) > 1.0e-7)
            return false;
        if (abs(pSubTable->tran3 - m_matrix[0][1]) > 1.0e-7)
            return false;
        if (abs(pSubTable->tran4 - m_matrix[1][1]) > 1.0e-7)
            return false;
        return true;
    }

    ////////////////////////////////////////////////////
    // Application / Execution
    ////////////////////////////////////////////////////

    void Transform(const SimplePoint & point, SimplePoint & newpoint) const
    {
        newpoint.x = point.x * m_matrix[0][0] + point.y * m_matrix[1][0] + m_matrix[2][0];
        newpoint.y = point.x * m_matrix[0][1] + point.y * m_matrix[1][1] + m_matrix[2][1];
    }

    void Transform(SimplePoint & point) const
    {
        SimplePoint newpoint;
        Transform(point, newpoint);
        point = newpoint;
    }

    void Transform(const SimpleRect & rect, SimpleRect & newrect) const
    {
        newrect.minX = rect.minX * m_matrix[0][0] + rect.minY * m_matrix[1][0] + m_matrix[2][0];
        newrect.minY = rect.minX * m_matrix[0][1] + rect.minY * m_matrix[1][1] + m_matrix[2][1];
        newrect.maxX = rect.maxX * m_matrix[0][0] + rect.maxY * m_matrix[1][0] + m_matrix[2][0];
        newrect.maxY = rect.maxX * m_matrix[0][1] + rect.maxY * m_matrix[1][1] + m_matrix[2][1];
    }

    void Transform(SimpleRect & rect) const
    {
        SimpleRect newrect;
        Transform(rect, newrect);
        rect = newrect;
    }

    void Transform(CPoint & point) const
    {
        SimplePoint newpoint(point);
        Transform(newpoint);
        point.x = (int)(newpoint.x > 0.0 ? newpoint.x + 0.5 : newpoint.x - 0.5);
        point.y = (int)(newpoint.y > 0.0 ? newpoint.y + 0.5 : newpoint.y - 0.5);
    }

    void Transform(SimplePoint point, CPoint & transformed) const
    {
        Transform(point);
        transformed.x = (int)(point.x > 0.0 ? point.x + 0.5 : point.x - 0.5);
        transformed.y = (int)(point.y > 0.0 ? point.y + 0.5 : point.y - 0.5);
    }

    void Transform(CPoint point, SimplePoint & transformed) const
    {
        transformed = point;
        Transform(transformed);
    }

    void Transform(double dx, double dy, double & x, double & y) const
    {
        SimplePoint point(dx, dy);
        Transform(point);
        x = point.x;
        y = point.y;
    }

    void Transform(double & x, double & y) const
    {
        SimplePoint point(x, y);
        Transform(point);
        x = point.x;
        y = point.y;
    }

    SimplePoint GetTransformed(SimplePoint point) const
    {
        Transform(point);
        return point;
    }

    CPoint GetTransformed(CPoint point) const
    {
        Transform(point);
        return point;
    }

    SimpleRect GetTransformed(const CRect & rect) const
    {
        return SimpleRect(GetTransformed(SimplePoint(rect.left, rect.bottom)), GetTransformed(SimplePoint(rect.right, rect.top)));
    }

    SimpleRect GetTransformed(double x1, double y1, double x2, double y2) const
    {
        return SimpleRect(GetTransformed(SimplePoint(x1, y1)), GetTransformed(SimplePoint(x2, y2)));
    }

    double GetTransformedX(double x, double y) const
    {
        return GetTransformed(SimplePoint(x, y)).x;
    }

    double GetTransformedY(double x, double y) const
    {
        return GetTransformed(SimplePoint(x, y)).y;
    }

    double GetTransformedX(int x, int y) const
    {
        return GetTransformed(SimplePoint(x, y)).x;
    }

    double GetTransformedY(int x, int y) const
    {
        return GetTransformed(SimplePoint(x, y)).y;
    }

    double GetTransformedX(const SimplePoint & point) const
    {
        return GetTransformed(point).x;
    }

    double GetTransformedY(const SimplePoint & point) const
    {
        return GetTransformed(point).y;
    }

    int GetTransformedIntX(double x, double y) const
    {
        CPoint point;
        Transform(SimplePoint(x, y), point);
        return point.x;
    }

    int GetTransformedIntY(double x, double y) const
    {
        CPoint point;
        Transform(SimplePoint(x, y), point);
        return point.y;
    }

    int GetTransformedIntX(const SimplePoint & point) const
    {
        CPoint pt;
        Transform(point, pt);
        return pt.x;
    }

    int GetTransformedIntY(const SimplePoint & point) const
    {
        CPoint pt;
        Transform(point, pt);
        return pt.y;
    }

protected:
    ////////////////////////////////////////////////////
    // Static Class Operations
    ////////////////////////////////////////////////////

    static const ThreeByThreeMatrix & GetIdentityMatrix();

    ////////////////////////////////////////////////////
    // Instance Variables
    ////////////////////////////////////////////////////

    ThreeByThreeMatrix  m_matrix;
};

Answer 1

设 A = (0, 0)，B = (1, 0)。通过矩阵变换两者得到A'和B'。测量 vector B' - A' 的角度。那应该给你角度。

要测量 vector 的角度，您可以使用atan2 (B'.y - A'.y, ​​B'.x - A'.x)