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# Transformation ( TRANSFORM )

Definition

There are three instantiations of TRANSFORM: transform (floating point kernel), rat_transform (rational kernel) and real_transform (real kernel). The respective header file name corresponds to the type name (with .h'' appended).

An instance T of type TRANSFORM is an affine transformation of two-dimensional space. It is given by a 3 x 3 matrix T with T2, 0 = T2, 1 = 0 and T2, 2 0 and maps the point p with homogeneous coordinate vector (px, py, pw) to the point T*p .

A matrix of the form realizes an translation by the vector (x/w, y/w) and a matrix of the form where a2 + b2 = w2 realizes a rotation by the angle about the origin, where cos = a/w and sin = b/w . Rotations are in counter-clockwise direction.

#include < LEDA/geo/generic/TRANSFORM.h >

Creation

 TRANSFORM T creates a variable introduces a variable T of type TRANSFORM. T is initialized with the identity transformation. TRANSFORM T(const INT_MATRIX t) introduces a variable T of type TRANSFORM. T is initialized with the matrix t . Precondition t is a 3 x 3 matrix with t2, 0 = t2, 1 = 0 and t2, 2 0 .

Operations

 INT_MATRIX T.T_matrix() returns the transformation matrix void T.simplify() The operation has no effect for transform. For rat_transform let g be the ggT of all matrix entries. Cancels out g . RAT_TYPE T.norm() returns the norm of the transformation TRANSFORM T(const TRANSFORM& T1) returns the transformation ToT1 . POINT T(const POINT& p) returns T(p) . VECTOR T(const VECTOR& v) returns T(v) . SEGMENT T(const SEGMENT& s) returns T(s) . LINE T(const LINE& l) returns T(l ) . RAY T(const RAY& r) returns T(r) . CIRCLE T(const CIRCLE& C) returns T(C) . POLYGON T(const POLYGON& P) returns T(P) . GEN_POLYGON T(const GEN_POLYGON& P) returns T(P) .

Non-member Functions

In any of the function below a point can be specified to the origin by replacing it by an anonymous object of type POINT, e.g., rotation90(POINT()) will generate a rotation about the origin.

 TRANSFORM translation(const INT_TYPE& dx, const INT_TYPE& dy, const INT_TYPE& dw) returns the translation by the vector (dx/dw, dy/dw) . TRANSFORM translation(const RAT_TYPE& dx, const RAT_TYPE& dy) returns the translation by the vector (dx, dy) . TRANSFORM translation(const VECTOR& v) returns the translation by the vector v . TRANSFORM rotation(const POINT& q, double alpha, double eps) returns the rotation about q by an angle alpha eps . TRANSFORM rotation90(const POINT& q) returns the rotation about q by an angle of 90 degrees. TRANSFORM reflection(const POINT& q, const POINT& r) returns the reflection across the straight line passing through q and r . TRANSFORM reflection(const POINT& q) returns the reflection across point q .     Next: Point Generators ( point Up: Basic Data Types for Previous: Geometry Algorithms ( geo_alg   Contents   Index
Christian Uhrig 2017-04-07