Calibrate Linear Scale

The Calibrate Linear Scale command works interactively to calibrate a linear coordinate scale for the image. The calibration is computed by drawing a line ("vector") of target length and specifying the world coordinate units and distance along the vector. The resulting calibration has equal scale 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.

Procedure

Click the button on the Image Tools Toolbar or use the Coordinates > Calibrate Linear Scale menu command.
Immediately after this command is executed, the following prompt is opened:

Mouse down at the fist point, drag to the final point, and release the mouse button.
After releasing the button to complete the line, Mira opens the Calibrate Linear Scale dialog shown below.
After clicking [OK], the world coordinate reference is set to (0,0) at the image corner. 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).

Callibrate Llinear 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. The example above shows the label Distance [units] updated to Distance [arcsec] using the name specified in the Units history box.
Units	The world coordinate units to use. You can choose a value from the list box or enter units.
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 to replace any existing WCS. The new calibration may be reversed using Edit > Undo (Ctrl+Z) to restore the previous coordinate system. To permanently save the arcsecond calibration to the image file, save the image in the normal way. You can repeat the calibration any number of times without having to manually delete the existing World Coordinate System calibration. To delete this or any other WCS calibration, use the Delete WCS command.

Command Properties

The Calibrate Linear Scale command includes two properties that compute subpixel-accurate centroid positions for the starting or ending points of the mouse-drawn line. These are useful if the image contains bright fiducial point markers for referenceing exact image distance. These are set from the Calibrate Linear Scale drop menu next to the command button on the Image Measurement toolbar. The centroid parameters use values from the Centroid Properties dialog for the Image Window. The Draw Calibration Line command duplicates the function of the command button.

Procedure

Command Properties

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