Setting the Markers

xyscan does not know anything about the content of the plot other than its size and the color/gray value of each pixel. In order to make a coordinate transformation, i.e. to translate the position of the cursor from local to plot coordinates, it needs the plot and local (pixel) coordinates of 4 points. From then on it is simple mathematics and xyscan will display local and plot coordinates as you move the cursor over the plot.

There are 2 markers for the x-axis (red), x1 (leftmost-x) and x2 (rightmost-x), and 2 markers for the y-axis (blue), y1 (lower-y) and y2 (upper-y). The figure below shows a screenshotwith all 4 markers set along the axes.

To place a marker, move the cursor along the x- or y-axis and stop exactly at the intersection between the axis line and a tic mark. Although an x-axis marker is mainly used to define a reference point in x, its y position matters since it is used to determine a possible tilt of the x-axis with respect to the canvas (same for y-axis of course). After you positioned the cursor press the Set button of the referring marker in the Settings window (see Component Overview). An input dialog pops up in which you have to type the position of the marker in plot coordinates. For the example depicted in the figure above x1 = 0, x2 = 0.35, y1 = 0, and y2 = 1.2. You can place the markers in any order but make sure that x1 < x2 and y1 < y2. The x1 and x2 marker are red, y1 and y2 are rendered in blue. Once a marker is set, the coordinate you assigned is displayed in the Settings window. Markers can sit on top of each other. If you think a marker is not properly placed you can set it again at any time.

Once all 4 markers are set, xyscan will start to display the plot coordinates of the current cursor position in the Coordinates window (see Component Overview).

Hint: the further away x1 and x2 (y1 and y1) are from each other the higher the precision of the scan.