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

Contour of an object as chain code.

The operator fetch_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 fetch_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).
Range of values: 0 <= Chain <= 7


Result

The operator fetch_chain normally returns the value TRUE. If more than one connection component is passed an exception is caused. 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.


Possible Predecessors

sobel_amp, threshold__, skeleton, edges__, rectangle1, circle


Possible Successors

approx_chain1, approx_chain2


See also

copy_obj, fetch_contour, fetch_polygon



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