Arc Edge Locator Polarity does not affect the Edge Score, but only edges that meet the selected Polarity are output as valid edges, regardless of their scores. l Dark to Light will only accept edges occurring at transitions from a dark area to a light area. l Light to Dark will only accept edges occurring at transitions from a light area to a dark area. l Either will accept any edge, regardless of polarity. Edge Polarity Edge Score Constraints There are two types of constraints: Position and Magnitude. You can set the tool to use only one constraint or both. A graphical function editor is provided for viewing and setting each type of constraint.
l If only one constraint is selected, edges are scored based on the selected constraint. l If both constraints are selected, each constraint accounts for 50% of the edge score. Magnitude Constraint The Magnitude constraint is based on edge values relative to the Magnitude Threshold. Edges having a magnitude equal to or exceeding the Magnitude Threshold are given a score of 1. Edges with values below the Magnitude Threshold receive a score ranging from 0 to 0.999, according to a manually set magnitude constraint function. The Magnitude Constraint is applied globally to all edges detected. The following figure shows two different setups for a magnitude constraint func- tion.
To set the Magnitude Constraint: ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 379