Calibrate Linear Scale

The Calibrate Linear Scale command works interactively to calibrate a linear pixel scale for the image. The calibration is computed by drawing a line ("vector") of target length and specifying the world coordinate distance along the vector. The resulting calibration has equal units in both x and y coordinates and is saved to the image header as a World Coordinate System. The coordinate units are specified in the calibration dialog. The window can be horizontally resized to accommodate long Units strings.

Procedure

  1. Click the btn_calibrate.png button on the Image Tools Toolbar or use the Coordinates > Calibrate Linear Scale menu command.

  2. Click the this command is executed, the command opens the prompt shown below.

  4. Mouse down at the fist point, drag to the final point, and release the mouse button.

  5. After releasing the button to finish the line, Mira opens the Calibrate Linear Scale dialog shown below.

     

Calibrate Linear Scale Properties

Distance, [units]

The distance in target coordinates corresponding to the line drawn on the image. The name from the Units field is listed in the caption.

Units

The world coordinate units to use. You can choose a value from the list box or enter units. Be aware that a long unit name may appear truncated in the real-time coordinate readout of the Image Toolbar.

Measured [pixels]

Specifies the length of the line in units of image pixels.

Scale

This field reports the calculated image scale. You can also override the calculated value by entering a replacement. The name from the Units field is listed in the caption to the right of the value.

This command applies a World Coordinate System ("WCS") calibration to the image or image set. This calibration replaces any existing WCS. The calibration applies only to the image in memory and does not become permanently affixed to the image until you save the image to a file. This command creates an Undo copy so that you can use the Edit > Undo (Ctrl+Z) command to restore the previous coordinate system. After clicking [OK] or [Apply], the world coordinate reference is set to (0,0) at the image edge. Since pixel (1,1) occurs at the center of the corner pixel, world coordinate (0,0) is located at pixel coordinate (-0.5,-0.5).

You can repeat the calibration any number of times without having to manually delete the existing World Coordinate System calibration. See the Delete WCS command.

Related Topics

Coordinate Systems, Set Linear Scale, Set Equatorial Scale, World Coordinate System