# Find the Expected Line

Once the calipers are placed, the Find Line tool runs each caliper to find an edge point. By default, the tool assumes that the line is the only edge point inside the caliper. If there are multiple edges inside the input region, you must specify caliper parameters that will return the desired edge first.

The following figure is an example of an expected line with four calipers. The example purposely uses an expected line angle somewhat different from the actual line angle to illustrate the angle tolerance you have to work with. The critical factors include making sure the image line edge falls inside each caliper, and ensuring no other features inside the calipers might be mistaken for a line edge.

The following figure shows the edge points found after the tool runs the calipers.

The found edge points are then applied to the Find Line tool which fits an infinite length line to the points.

The infinite length line shown in this figure is shortened to a line segment using a projection of the expected line. The projection is performed by determining the point on the found line that is closest to the midpoint of the expected line, then using that as the midpoint of a segment of the expected length along the found line. The following figure shows how the expected line length is used to establish the found line segment.