profoundGetEllipse: Calculate single annulus properties of an iso-photal ellipse
In ProFound: Photometry Tools

Description Usage Arguments Details Value Author(s) See Also Examples

Returns single ellipse properties for a specific set of pixels, assumed to be be a narrow range in flux (i.e. an iso-photal annulus).

1 2	profoundGetEllipse(x, y, z, xcen = NULL, ycen = NULL, scale = sqrt(2), pixscale = 1, dobox = FALSE, plot=FALSE, ...)

`x`	Numeric vector; x values of pixels. If this is a 3 column matrix then column 1 is used for x, column 2 is used for y and column 3 is used for val, see Examples.
`y`	Numeric vector; y values of pixels.
`z`	Numeric vector; z values of pixels. This is effectively the height, and would be the pixel flux for an image.
`xcen`	Numeric scalar; the desired x centre of the ellipse. If this is not provided it is calculated internally.
`ycen`	Numeric scalar; the desired y centre of the ellipse. If this is not provided it is calculated internally.
`scale`	How should the standard ellipse covariance be scaled to create a geometric ellipse. The default of sqrt(2) is appropriate to create an ellipse that represents the location of an iso-photal contour of a galaxy.
`pixscale`	Numeric scalar; the pixel scale, where pixscale=asec/pix (e.g. 0.4 for SDSS). If set to 1 (default), then the output radhi, radlo and radav is in terms of pixels, otherwise they are in arcseconds.
`dobox`	Logical; should boxiness be computed? If FALSE then boxiness is fixed to be 0. If TRUE then boxiness is computed (and other parameters are refined) using a maximum likelihood method. This is more expensive to compute, so the default is FALSE.
`plot`	Logical; should an ellipse be drawn on the current plot? This plot is generated by the `profoundDrawEllipse` function.
`...`	Further arguments to be passed to `profoundDrawEllipse`. Only relevant is plot=TRUE.

The assumption is this function will largely be used by the profoundGetEllipses function, but it could be useful for computing the shape of a particular iso-photal contour (see Examples).

A numeric vector with the following named elements:

`xcen`	The flux weighted x centre of the ellipse.
`ycen`	The flux weighted y centre of the ellipse.
`radhi`	The major axis extent of the ellipse (units of pixscale, so if pixscale represents the standard asec/pix this will be asec).
`radlo`	The minor axis extent of the ellipse (units of pixscale, so if pixscale represents the standard asec/pix this will be asec).
`radav`	The average radius of the ellipse (units of pixscale, so if pixscale represents the standard asec/pix this will be asec).
`axrat`	The axial ratio of the ellipse as given by radlo/radhi.
`ang`	The angle of the ellipse in the usual ProFit sense, see `profitMakeModel`.
`box`	The boxiness of the ellipse in the usual ProFit sense, see `profitMakeModel`.
`xsd`	The flux weighted standard deviation in x (always in units of pix).
`xsd`	The flux weighted standard deviation in y (always in units of pix).
`covxy`	The flux weighted covariance in xy (always in units of pix).
`corxy`	The flux weighted correlation in xy (always in units of pix).

Aaron Robotham

profoundGetEllipses, profoundGetEllipsesPlot

## Not run: 
# We need the ProFit library to show the profile: library(ProFit)
image = readFITS(system.file("extdata", 'KiDS/G266035fitim.fits',
package="ProFit"))$imDat
tempxy=cbind(which(image>2e-11 & image<3e-11, arr.ind=TRUE)-0.5,
             image[image>2e-11 & image<3e-11])
magimage(image>2e-11 & image<3e-11)
points(tempxy[,1:2], pch='.', col='red')
tempellipse=profoundGetEllipse(tempxy)
profoundDrawEllipse(tempellipse['xcen'], tempellipse['ycen'], tempellipse['radhi'],
                      tempellipse['axrat'], tempellipse['ang'], col='blue')

## End(Not run)