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

## Description

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).

## Usage

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

## Arguments

 `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.

## Details

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).

## Value

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).

## Author(s)

Aaron Robotham

`profoundGetEllipses`, `profoundGetEllipsesPlot`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13``` ```## 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) ```