## Engauge Digitizer - Glossary

axis point
  Point that is added to a graph to define the scale. The two coordinate values must be defined for each axis point. Three axis points are needed to define the scales in the two coordinate directions
collinear
  Collinear points lie along a straight line. The three axis points cannot be collinear because graph coordinates are therefore impossible to compute.
collocated
  Collocated points are close to each other or at the same location. Multiple axis points cannot share the same location because graph coordinates are therefore impossible to compute, and should be widely separated so computed graph coordinates are most accurate.
coordinates
  Two values used in a graph to specify position. If the coordinates are cartesian, the two values are X and Y. If the coordinates are polar, the two values are the radius R and the angle theta. The X, Y and R coordinates can be logarithmic
corner
  The point at the junction of two line segments in a piecewise linear curve
curve
  Continuous line in a graph or map. This is digitized by creating curve points along the line
curve point
  Point that is added to a graph on top of either a curve or point in the original image
digitize
  Process of converting non-digital data into numbers. The specific type of digitizing performed by Engauge Digitizer is the conversion of graph and map images into numbers. These numbers can be exported to spreadsheets and other math software
discretize
  Process that converts each pixel of an original image into either the black foreground, or the white background. The colors and grays of the original image are lost. By controlling discretizing, unwanted parts of the original image can be removed
engauge
  Process of converting an image file containing a graph or map into numbers. The word 'engauge' was invented to distinguish this process from other types of digitizing
export
  Process of copying digitized information from Engauge Digitizer to other software or a file
fast correlation
  A preferred method of performing template matching, which is identifying various places in an image where a template (or sample) appears. This method is fast because it uses a highly efficient Fast Fourier Transform, and is therefore used by Engauge to perform point matching.
graph
  Image having two coordinate directions. Three axis points define the scales in the two coordinate directions, and the location of the origin. Graphs have either points or curves
grid display
  Grid lines may be added to a graph after the axis points have been defined. Any errors while creating the axis points are usually apparent when grid lines are displayed
grid removal
  Process that removes the grid from an original graph image so automated digitizing techniques perform better
import
  Process of loading an original graph or map image into Engauge Digitizer
line graph
  Graph containing lines
line segment
  Part of a straight line that lies between two end points
map
  Image without any coordinates, and having the same scale in any direction. A scale bar defines the scale in a map
measure
  Set of one or more connected line segments that is used to measure distance and/or area in a graph or map
piecewise linear
  Curve that is composed of multiple line segments. A graph of the absolute value function is a simple example of a piecewise linear curve
point graph
  Graph containing distinct points in the original image
point match
  Automated digitizing technique used on graphs containing points. The user selects a representative sample point, and then similar points are automatically digitized starting with the closest match
resolution
  The distance in graph units corresponding to the pixel separation of the original image. This distance is displayed in the status bar, since it represents the accuracy of the graph measurements
sample point
  The point, chosen by the user during point matching, that best represents the points to be matched
scale
  Relationship between the actual distance on the graph or map, and the represented units. Typically, actual distance is measured in pixels on the screen, or centimeters or inches on a printout. The represented units may be distance, time, percent, counts, ...
scale bar
  Line segment that defines the scale of a map
segment
  Piece of a curve, in a graph, that can be automatically digitized using segment fill mode. A segment is a set of adjoining points that lie between two endpoints
segment fill
  Process of automatically digitizing a curve in a graph, by creating curve points along each segment along the curve
select mode
  Digitizing mode in which existing points can be selected by clicking on an individual points, or clicking and dragging to select all points in a box. Shift-click adds a new point to the points that are already selected. The control key temporarily hides points that do not belong to the currently selected curve.
session
  Period of time spent using Engauge Digitizer, from starting the software to stopping it