Setting axes

You must calibrate the axes by defining their scales so that the application can correctly map the image pixels to the corresponding data values in the image.

The Graph Digitizer supports the Cartesian (one x-axis and one y-axis) coordinate system.

Note

Plots with non-orthogonal axes, plots rotated at an angle, or images with perspective distortions are not correctly supported. You can use image editing tools to correct the image before using the Graph Digitizer.

Defining axis ranges

For the axis ranges, you must set two points on the x-axis and two points on the y-axis. Giving the data values at the positions of the four points helps the application to map the image pixels corresponding to data points to their actual values when the curve is digitized.

After the image is loaded, two lines with symbols at their ends are displayed at the bottom left of the image. The blue line is used for the x-axis and the orange line for the y-axis. The symbols are manipulators that allow you to mark the position of the points - one start point (square) and one end point (circle). The shape of the symbols refers to the fields in which you have to enter the values in the left panel.

Figure 1: Manipulators for axis scales

To move a manipulator:

1. Click on a manipulator and hold down the mouse button.

2. Drag the mouse to the position you want the manipulator to be on the axis graduation of the graph.

3. Release the button. Note A manipulator remains selected even after releasing the mouse button. When selected, the manipulator shape is shaded around the symbol to highlight it.

4. While the manipulator is selected, you can also make fine adjustments to the position of the point using the Arrow keys to refine the manipulator position pixel-wise. Note After an image is loaded, a magnifying glass is activated by default, identified by a zoom view delimited by a reticule shape. It helps you to improve the accuracy of the pixel selection. You can toggle the magnifying glass by pressing Z on your keyboard or click the reticule button at the top right of the image view. When a manipulator is selected the reticule of the zoom view is blue, otherwise it is black.

5. Press Return to apply the position and release the selection, or click anywhere on the image.

For better accuracy, pick points that are as far away from each other as possible.

After you set the positions of the four points, you can enter the values at these points in the left-hand panel.

Select logarithmic, if the x-axis or y-axis is defined on a logarithmic scale.

Figure 2: Axis settings panel

Note

Unit setting is not mandatory and can be done when exporting the data values to a data table file. These units must be part of the Simcenter Amesim units database.