Engauge Digitizer - Digitizing Line Graphs

Typical Set of Steps To Digitize Line Graphs

The following steps digitize a linear cartesian graph with one curve:

• Obtain an image file (bitmap, jpeg or other) showing one or more curves and both axes
• Import the image file using one of the following options:
  • File/Import menu option
  • Copying and pasting
  • Dragging and dropping
• Click on the Axes Point button before entering axes points. These will define the coordinate system
• Click on one of the axes to add the first axes point, then enter its graph coordinates
• Click on one of the axes to add the second axes point, then enter its graph coordinates
• Click on one of the axes to add the third axes point, then enter its graph coordinates
• Click on the Segment Fill button to automatically digitize entire curve segments at a time.
• Click on a segment underneath the cursor to fill that segment with a set of curve points. Repeat until the segments have been digitized.
• Click on the Curve Points button to manually enter curve points.
• Click on the curve to add a curve point. Repeat until the curve is covered with a sufficient number of curve points
• Export curve points using one of the following options:
  • File/Export menu option to save selected curves into a tabular text file
  • Copying and pasting to copy points in the current curve from the curve geometry window to another application
  • Dragging and dropping to copy points in the current curve from the curve geometry window to another application

Optional Steps

To clean up the image for better performance of Segment Fill and Point Match: steps:

• Show the processed image, rather than the original image, by selecting the View/Processed Image menu option
• Adjust the discretize settings using the Settings/Discretize menu option, until unwanted parts of the image disappear
• Remove grid lines using the Settings/Grid Removal menu option

For a graph that is logarithmic or polar:

• Select the Settings/Coords menu option to bring up the coordinates window
• Select the appropriate coordinate settings

For a graph with more than one curve:

• Select the Settings/Curves menu option to bring up the curves window
• Click on the New button to create a new curve, then enter the name of the new curve
• Repeat the previous step until all desired curve names have been entered
• In the main window, use the Curves combobox to select a curve. While that curve is selected, all new curve points will be assigned to that curve