connect_grid_points — Establish connections between the grid points of the rectification grid.
connect_grid_points searches for connecting lines between the grid points (Row,Column) of the rectification grid. The connecting lines are extracted from the input image Image by a combination of an edge detector, a smoothing filter, and a line detector, each of size . The to be used is determined as follows: When a single value is passed in Sigma, this value is used. When a tuple of three values ('sigma_min', 'sigma_max', 'sigma_step') is passed, connect_grid_points tests every within a range from 'sigma_min' to 'sigma_max' with a step width of 'sigma_step' and chooses the that causes the greatest number of connecting lines. The same happens when a tuple of only two values 'sigma_min' and 'sigma_max' is passed. However, in this case a fixed step width of 0.05 is used.
Then, the extracted connecting lines are split at the grid points and those line segments are selected that start as well as end at a grid point. Note that edge detectors typically don't work very accurately in the proximity of edge junctions, and thus in general the connecting lines will not hit the grid points. Therefore, actually those connecting lines are split and selected that start at, end at, or pass a grid point at a maximum distance of MaxDist. The connecting lines are modified in order to start and end exactly in the corresponding grid points, and are returned in ConnectingLines as XLD contours.
Additionally, connect_grid_points calculates for each output XLD contour its type of transition and stores it in its global attribute 'bright_dark'. The attribute is set to 1.0, if the connecting line forms a bright-dark transition (left to right, viewed from start point to end point), otherwise it is set to 0.0.
For a reliable determination of the type of bright-dark transition as well as for the following rectification, it is necessary that each connecting line has at least three contour points. Therefore, connecting lines with only two contour points are not returned. Note, that the parameter MaxDist has a substantial influence on the length of the returned connecting lines, because all contour points of a possible connecting line that are closer than MaxDist to a grid point are replaced by one single contour point. If MaxDist is too big, some of the connecting lines might get lost.
Row coordinates of the grid points.
Column coordinates of the grid points.
Restriction: number(Column) == number(Row)
Size of the applied Gaussians.
Number of elements: 1 <= Sigma && Sigma <= 3
Default value: 0.9
Suggested values: 0.7, 0.9, 1.1, 1.3, 1.5
Restriction: 0.7 <= Sigma
Maximum distance of the connecting lines from the grid points.
Default value: 5.5
Suggested values: 1.5, 3.5, 5.5, 7.5, 9.5
Restriction: 0.0 <= MaxDist
connect_grid_points returns 2 (H_MSG_TRUE) if all parameter values are correct. If necessary, an exception is raised.