Operator Reference
affine_trans_contour_xld (Operator)
affine_trans_contour_xld — Apply an arbitrary affine 2D transformation to XLD contours.
Signature
affine_trans_contour_xld(Contours : ContoursAffineTrans : HomMat2D : )
Description
affine_trans_contour_xld applies an arbitrary affine 2D
transformation, i.e., scaling, rotation, translation, and slant (skewing), to
the XLD contours given in Contours and returns the transformed
contours in ContoursAffineTrans. The affine transformation is
described by the homogeneous transformation matrix given in
HomMat2D, which can be created using the operators
hom_mat2d_identity, hom_mat2d_scale,
hom_mat2d_rotate, hom_mat2d_translate, etc., or be the result
of operators like vector_angle_to_rigid.
The components of the homogeneous transformation matrix are interpreted as follows: The row coordinate of the image corresponds to x and the column coordinate corresponds to y of the coordinate system in which the transformation matrix was defined. This is necessary to obtain a right-handed coordinate system for the image. In particular, this assures that rotations are performed in the correct direction. Note that the (x,y) order of the matrices quite naturally corresponds to the usual (row,column) order for coordinates in the image.
Attention
affine_trans_contour_xld does not use the HALCON standard
coordinate system (with the origin in the center of the upper left
pixel), but instead uses the same coordinate system as in
affine_trans_pixel, i.e., the origin lies in the upper
left corner of the upper left pixel. Therefore,
applying affine_trans_contour_xld corresponds to
a chain of transformations (see affine_trans_pixel), which is applied
to each point of the contour (input and output pixels as homogeneous
vectors). As an effect, you might get unexpected results when creating affine
transformations based on coordinates that are derived from the
contour, e.g., by operators like
area_center_xld. For example, if you use this operator to calculate
the center of gravity of a rotationally symmetric XLD contour and then rotate
the contour around this point using hom_mat2d_rotate, the resulting
contour will not lie on the original one. In such a case, you can compensate
this effect by applying the following translations to HomMat2D
before using it in affine_trans_contour_xld:
hom_mat2d_translate(HomMat2D, 0.5, 0.5, HomMat2DTmp)
|
hom_mat2d_translate_local(HomMat2DTmp, -0.5, -0.5, HomMat2DAdapted)
|
affine_trans_contour_xld(Contours, ContoursAffineTrans, HomMat2DAdapted)
|
For an explanation of the different 2D coordinate systems used in HALCON, see the introduction of chapter Transformations / 2D Transformations.
Execution Information
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Automatically parallelized on tuple level.
Parameters
Contours (input_object) xld_cont(-array) → object
Input XLD contours.
ContoursAffineTrans (output_object) xld_cont(-array) → object
Transformed XLD contours.
HomMat2D (input_control) hom_mat2d → (real)
Input transformation matrix.
Result
If the matrix HomMat2D represents an affine transformation
(i.e., not a projective transformation),
affine_trans_contour_xld returns 2 (
H_MSG_TRUE)
. If the input is
empty the behavior can be set via
set_system(::'no_object_result',<Result>:). If necessary,
an exception is raised.
Possible Predecessors
hom_mat2d_identity,
hom_mat2d_translate,
hom_mat2d_rotate,
hom_mat2d_scale,
hom_mat2d_reflect
See also
affine_trans_image,
affine_trans_region
Module
Foundation