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.
Centroid
Measurements
