get_region_chain (Operator)

Name

get_region_chain — Contour of an object as chain code.

Synopsis

get_region_chain(Region : : : Row, Column, Chain)

Description

The operator get_region_chain returns the contour of a region. A contour is a series of pixels describing the outline of the region. The contour “lies on” the region. It starts at the smallest line number; in that line at the pixel with the largest column index. The rotation occurs clockwise. Holes of the region are ignored. The direction code (chain code) is defined as follows:

                        3       2       1
                        4       *       0
                        5       6       7

The operator get_region_chain returns the code in the form of a tuple. In case of an empty region the parameters Row and Column are zero and Chain is the empty tuple.

Attention

Holes of the region are ignored. Only one region may be passed, and it must have exactly one connection component.

Parameters

Region (input_object)	region → object
Region to be transformed.

Row (output_control)	chain.begin.y → (integer)
Line of starting point.

Column (output_control)	chain.begin.x → (integer)
Column of starting point.

Chain (output_control)	chain.code-array → (integer)
Direction code of the contour (from starting point).
Typical range of values: 0 ≤ Chain ≤ 7

Result

The operator get_region_chain normally returns the value 2 (H_MSG_TRUE). If more than one connection component is passed an exception is raised. The behavior in case of empty input (no input regions available) is set via the operator set_system('no_object_result',<Result>). The behavior in case of empty region (the region is the empty set) is set via the operator set_system('empty_region_result',<Result>). If necessary an exception is raised.

Parallelization Information

get_region_chain is reentrant and processed without parallelization.

Possible Predecessors

sobel_amp, threshold, skeleton, edges_image, gen_rectangle1, gen_circle

Possible Successors

approx_chain, approx_chain_simple

See also

copy_obj, get_region_contour, get_region_polygon

Module

Foundation