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7.4.6.2 Position measurements in pixels ¶

The position of a labeled region within your input dataset (in its own units) can be measured with the options in this section. By “in its own units” we mean pixels in a 2D image or voxels in a 3D cube. For example if the flux-weighted center of a label lies 123 pixels on the horizontal and 456 pixels on the vertical, the --x and --y options will put a value of 123 and 456 in their respective columns. As you see below, there are various ways to define the “position” of an object, so read the differences carefully to choose the one that corresponds best to your usage.

-x

--x

The flux weighted center of all objects and clumps along the first FITS axis (horizontal when viewed in SAO DS9), see \(\overline{x}\) in Measuring elliptical parameters. The weight has to have a positive value (pixel value larger than the Sky value) to be meaningful! Specially when doing matched photometry, this might not happen: no pixel value might be above the Sky value. For such detections, the geometric center will be reported in this column (see --geo-x). You can use --weight-area to see which was used.

-y

--y

The flux weighted center of all objects and clumps along the second FITS axis (vertical when viewed in SAO DS9). See --x.

-z

--z

The flux weighted center of all objects and clumps along the third FITS axis. See --x.

--geo-x

The geometric center of all objects and clumps along the first FITS axis axis. The geometric center is the average pixel positions irrespective of their pixel values.

--geo-y

The geometric center of all objects and clumps along the second FITS axis axis, see --geo-x.

--geo-z

The geometric center of all objects and clumps along the third FITS axis axis, see --geo-x.

--min-val-x

Position of pixel with minimum value in objects and clumps, along the first FITS axis.

--max-val-x

Position of pixel with maximum value in objects and clumps, along the first FITS axis.

--min-val-y

Position of pixel with minimum value in objects and clumps, along the first FITS axis.

--max-val-y

Position of pixel with maximum value in objects and clumps, along the first FITS axis.

--min-val-z

Position of pixel with minimum value in objects and clumps, along the first FITS axis.

--max-val-z

Position of pixel with maximum value in objects and clumps, along the first FITS axis.

--min-x

The minimum position of all objects and clumps along the first FITS axis.

--max-x

The maximum position of all objects and clumps along the first FITS axis.

--min-y

The minimum position of all objects and clumps along the second FITS axis.

--max-y

The maximum position of all objects and clumps along the second FITS axis.

--min-z

The minimum position of all objects and clumps along the third FITS axis.

--max-z

The maximum position of all objects and clumps along the third FITS axis.

--clumps-x

[Objects] The flux weighted center of all the clumps in this object along the first FITS axis. See --x.

--clumps-y

[Objects] The flux weighted center of all the clumps in this object along the second FITS axis. See --x.

--clumps-z

[Objects] The flux weighted center of all the clumps in this object along the third FITS axis. See --x.

--clumps-geo-x

[Objects] The geometric center of all the clumps in this object along the first FITS axis. See --geo-x.

--clumps-geo-y

[Objects] The geometric center of all the clumps in this object along the second FITS axis. See --geo-x.

--clumps-geo-z

[Objects] The geometric center of all the clumps in this object along the third FITS axis. See --geo-z.