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7.4.6.7 Morphology measurements (elliptical) ¶

When your target objects are sufficiently ellipse-like, you can use the measurements below to quantify the various parameters of the ellipse. For details of how the elliptical parameters are measured, see Measuring elliptical parameters. For non-parametric morphological measurements, see Morphology measurements (non-parametric). The measures that start with --geo-* ignore the pixel values and just do the measurements on the label’s “geometric” shape.

--semi-major

The pixel-value weighted root mean square (RMS) along the semi-major axis of the profile (assuming it is an ellipse) in units of pixels.

--semi-minor

The pixel-value weighted root mean square (RMS) along the semi-minor axis of the profile (assuming it is an ellipse) in units of pixels.

--axis-ratio

The pixel-value weighted axis ratio (semi-minor/semi-major) of the object or clump.

--position-angle

The pixel-value weighted angle of the semi-major axis with the first FITS axis in degrees.

--geo-semi-major

The geometric (ignoring pixel values) root mean square (RMS) along the semi-major axis of the profile, assuming it is an ellipse, in units of pixels.

--geo-semi-minor

The geometric (ignoring pixel values) root mean square (RMS) along the semi-minor axis of the profile, assuming it is an ellipse, in units of pixels.

--geo-axis-ratio

The geometric (ignoring pixel values) axis ratio of the profile, assuming it is an ellipse.

--geo-position-angle

The geometric (ignoring pixel values) angle of the semi-major axis with the first FITS axis in degrees.