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diff --git a/src/transf_mat_3x4.h b/src/transf_mat_3x4.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef SEEN_TRANSF_MAT_3x4_H
+#define SEEN_TRANSF_MAT_3x4_H
+
+/*
+ * 3x4 transformation matrix to map points from projective 3-space into the projective plane
+ *
+ * Authors:
+ *   Maximilian Albert <Anhalter42@gmx.de>
+ *
+ * Copyright (C) 2007  Authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "proj_pt.h"
+#include "axis-manip.h"
+
+namespace Proj {
+
+class TransfMat3x4 {
+public:
+    TransfMat3x4();
+    TransfMat3x4(Pt2 vp_x, Pt2 vp_y, Pt2 vp_z, Pt2 origin);
+    TransfMat3x4(TransfMat3x4 const &rhs);
+    Pt2 column (Proj::Axis axis) const;
+    Pt2 image (Pt3 const &point);
+    Pt3 preimage (Geom::Point const &pt, double coord = 0, Axis = Z);
+    void set_image_pt (Proj::Axis axis, Proj::Pt2 const &pt);
+    void toggle_finite (Proj::Axis axis);
+    double get_infinite_angle (Proj::Axis axis) {
+        if (has_finite_image(axis)) {
+            return Geom::infinity();
+        }
+        Pt2 vp(column(axis));
+        return Geom::atan2(Geom::Point(vp[0], vp[1])) * 180.0/M_PI;
+    }
+    void set_infinite_direction (Proj::Axis axis, double angle) { // angle is in degrees
+        if (tmat[2][axis] != 0) return; // don't set directions for finite VPs
+
+        double a = angle * M_PI/180;
+        Geom::Point pt(tmat[0][axis], tmat[1][axis]);
+        double rad = Geom::L2(pt);
+        set_image_pt(axis, Proj::Pt2(cos (a) * rad, sin (a) * rad, 0.0));
+    }
+    inline bool has_finite_image (Proj::Axis axis) { return (tmat[2][axis] != 0.0); }
+
+    char * pt_to_str (Proj::Axis axis);
+
+    bool operator==(const TransfMat3x4 &rhs) const;
+    TransfMat3x4 operator*(Geom::Affine const &A) const;
+    TransfMat3x4 &operator*=(Geom::Affine const &A);
+
+    void print() const;
+
+    void copy_tmat(double rhs[3][4]);
+
+private:
+    // FIXME: Is changing a single column allowed when a projective coordinate system is specified!?!?!
+    void normalize_column (Proj::Axis axis);
+    inline void set_column (Proj::Axis axis, Proj::Pt2 pt) {
+        tmat[0][axis] = pt[0];
+        tmat[1][axis] = pt[1];
+        tmat[2][axis] = pt[2];
+    }
+    double tmat[3][4];
+};
+
+} // namespace Proj
+
+#endif /* __TRANSF_MAT_3x4_H__ */
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :