Centroid Measurements

The Centroid Measurement computes a high precision estimate of the position of a small object such as a point source. Centroid properties cam be changed using the Centroid Properties dialogs.

To make a centroid measurement, position the Image Cursor near the target object, then click on the toolbar or click Centroid in the Measure menu.
This command is also operated using the 'C' keystroke command when the Image Cursor is placed near the peak of a point source.

If an image set is open in the source Image Window, you can choose whether to measure only the active image or to measure the entire image set. If measuring the entire set, Mira finds each successive centroid by searching the next image within some radius of the current position.

NOTE

When the Image Cursor is used to measure centroid positions for an Image Set, the cursor position may appear to be inaccurate after being shifted within the individual images. This happens because the Image Cursor is a feature of the Image Window rather than the individual images. However, the centroid coordinates tabulated in the measurement grid are correct. In contrast, Point Measurements are calculated and marked independently on each image, so they indicate the measured coordinates in each image if the centroid option is enabled on the Centroid Properties page.

Measurement Results

Measurements are tabulated in the Centroid Measurements window as shown below. This is a Report Window with built-in functionality for sorting, rearranging, copying, and saving to a file..

In this example, the first 5 measurements show images having no World Coordinate System ("WCS") calibration. Measurements 6 through 10 shows the same measurements when the images do have a WCS calibration.

Measurements for all objects in all images and all Image Windows go into a single Report window. If you want to clear the Report window of prior measurements, make sure the window has focus, then click View > Clear in the menu.

The items in the Report window are described in the table below.

Quantities in the Centroid Table

#	The sequence number of the measurement.
Image	The name of the image that was measured
X	The X coordinate of the centroid position. If the image has a WCS calibration, this is right ascension, otherwise this is the column coordinate.
Y	The Y coordinate of the centroid position. If the image has a WCS calibration, this is declination, otherwise this is the row coordinate.
Value	The peak intensity of the object.
Col	The column coordinate of the centroid position
Row	The row coordinate of the centroid position.

Measurement Results

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