hough_lines🔗
Short description🔗
hough_lines — Detect lines in edge images with the help of the Hough transform and
returns it in HNF.
Signature🔗
hough_lines( region RegionIn, integer AngleResolution, integer Threshold, integer AngleGap, integer DistGap, out hesseline.angle.rad Angle, out hesseline.distance Dist )
Description🔗
The operator hough_lines allows the selection of line-like
structures in a region, whereby it is not necessary that the individual
points of a line are connected. This process is based on the Hough transform.
The parameter AngleResolution defines the degree of exactness
concerning the determination of the angles. It amounts to \(1 /
\textrm{AngleResolution}\) degree.
The parameter Threshold
determines by how many points of the original region a line’s hypothesis
must at least be supported in order to be selected into the output.
The parameters AngleGap and DistGap define a
neighborhood of the points in the Hough image in order to determine the
local maxima: AngleGap describes the minimum distance of two
maxima in the Hough image in angle direction and DistGap in
distance direction, respectively. Thus, maxima exceeding
Threshold but lying close to an even higher maximum are eliminated.
If multiple maxima in this neighborhood are equally high, all of them are
returned. This elimination can particularly be helpful when searching for
short and long lines simultaneously.
The lines are returned in Hessian Normal Form (HNF), that is by the direction
Angle and length Dist of their normal vectors.
Execution information🔗
Execution information
-
Multithreading type: reentrant (runs in parallel with non-exclusive operators).
-
Multithreading scope: global (may be called from any thread).
-
Processed without parallelization.
Parameters🔗
RegionIn (input_object) region → object
Binary edge image in which the lines are to be detected.
AngleResolution (input_control) integer → (integer)
Adjusting the resolution in the angle area.
Default: 4
List of values: 1, 2, 4, 8
Threshold (input_control) integer → (integer)
Threshold value in the Hough image.
Default: 100
Value range: 2 ≤ Threshold
AngleGap (input_control) integer → (integer)
Minimal distance of two maxima in the Hough image (direction: angle).
Default: 5
Value range: 0 ≤ AngleGap
DistGap (input_control) integer → (integer)
Minimal distance of two maxima in the Hough image (direction: distance).
Default: 5
Value range: 0 ≤ DistGap
Angle (output_control) hesseline.angle.rad-array → (real)
Angles (in radians) of the detected lines’ normal vectors.
Value range: -1.5707963 ≤ Angle ≤ 3.1415927
Dist (output_control) hesseline.distance-array → (real)
Distance of the detected lines from the origin.
Number of elements: Dist == Angle
Value range: 0 ≤ Dist
Result🔗
The operator hough_lines returns the value 2 (H_MSG_TRUE)
if the input is not empty.
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 is set via
set_system('empty_region_result',<Result>).
If necessary an exception is raised.
Combinations with other operators🔗
Combinations
Possible predecessors
Possible successors
See also
Module🔗
Foundation