# Caliper

A compound tool that contains a Profile tool which is connected to a MeasureGapWidths tool.

## Inputs

image
Input image.
startPoint
The location of the first point in world coordinates.
endPoint
The location of the last point in world coordinates.
width
The width of the caliper line line on XY-plane in world coordinates. If the width is zero, the line will be made of point samples. A non-zero width means that an average over the pixels that span width world units will be calculated.
interpolation
If true, improve accuracy by interpolating point samples between pixels along the line. If false, round pixel coordinates to the nearest integer.
algorithm
Gap edge detection algorithm. Gap edges are detected from filtered profile using the selected algorithm.
smoothness
Smoothness of the profile filter. Small smoothness value works best with sharp edges. Large smoothness value gives better results if the edges are dull or the image is noisy.
threshold
The following condition must be met at be met before a filtered profile entry is considered to be a start / end of a gap: Absolute mode: Filtered gray level must be larger than this. Differential mode: Rate of change must be larger than this. Gaussian zero crossing mode: Two consecutive 2nd order differences must be of opposite signs and their difference must be larger than threshold.
hysteresis
Hysteresis to the threshold Absolute mode: The threshold must be exceeded by this number before the pixel is considered an edge. Differential mode: Pixel at which the rate of change is local maximum minus hysteresis is set as an edge. Gaussian zero crossing mode: N/A
maxGapCount
maximum number of gaps to be detected

## Outputs

Supported algorithms

Enumerator
AbsoluteThreshold

Detect gap boundaries at positions where the given threshold gray level is crossed in either direction.

DifferentialThreshold

Detect gap boundaries at steepest gray level changes. Positive changes mean a dark-to-light boundary and negative changes a light-to-dark boundary.

GaussianZeroCross

Marr-Hildreth edge detector. First filters the input profile with a Gaussian filter whose width is changed according to the smoothness parameter. A second order differential function is then computed. Zero crossings of this differential function indicate the points at which the change of magnitude is the largest. These points are selected as boundaries.

 enum CaliperTool::GapType

Gap filter types

Enumerator
DarkGap

Report only dark gaps.

LightGap

Report only light gaps.

DarkOrLightGap

Report both gap types.