The circle measurement tool allows you to position two crosshairs, one marking the center of a circle and the other marking a point on the circumference of the circle. This tool is ideal for use with online maps. In addition, the screen area contained in the square bounding the circle can be captured to the clipboard. Both the data window attached to the crosshairs and Meazure’s tool information section will display the measurement information. The magnifier window will show the area around the crosshair that is being moved as well as the color of the pixel at the center of the crosshair.

The tool information section displays the following measurements for the Circle tool:

• XV, YV - The position of the crosshair at the center of the circle
• X1, Y1 - The position of the Point 1 crosshair on the circumference of the circle
• W, H - The width and height of the bounding square. W = H = 2 * D
• D - The radius of the circle. D = W / 2
• A - The angle of the radius relative to the x-axis. Using the default coordinate system, positive angles are measured clockwise from the positive x-axis to the line from center of the circle to Point 1 on the circumference
• Ar - The area of the circle. Ar = pi * D²

Note that the calculation of W, H, D and Ar is always performed in pixel units and the result is converted to the currently selected display units.

To capture the screen area bounded by the circle to the clipboard, select the Copy Region item from the Edit menu or press Ctrl+R.

The mouse or keyboard can be used to position the crosshairs and fine adjustment can be made with the up/down buttons adjacent to the position text fields. When using the mouse to drag a crosshair, the SHIFT key can be used to lock the motion to the horizontal or vertical direction. In addition, the entire rectangle can be moved by pressing the CTRL key while dragging one of the crosshairs.

To select the Circle tool choose the Circle item on the Tools menu or click on the Circle tool icon on the toolbar.