R/get.fwhm.R

In AngusWright/LAMBDAR: Measure galaxy fluxes from an arbitrary FITS image using input aperture locations and dimensions

get.fwhm<-
function(zdist,centre){
#Details {{{
#function returns the FHWM of the image from
#*maxima*, in pixels.
#}}}
  
  if (!is.null(dim(zdist)) && !any(dim(zdist)==0)) {
    #Setup Radius-map {{{
    if (missing(centre)||length(centre)!=2) { 
      centre<-as.numeric(which(zdist==max(zdist), arr.ind=TRUE))
    }
    im.rad.x<-min(centre[1],length(zdist[,1])-centre[1])-1
    im.rad.y<-min(centre[2],length(zdist[1,])-centre[2])-1
    lim<-c(centre[1]-im.rad.x, centre[1]+im.rad.x, centre[2]-im.rad.y, centre[2]+im.rad.y)
    x = try(seq(floor(-im.rad.x), floor(im.rad.x), length=im.rad.x*2+1))
    y = try(seq(floor(-im.rad.y), floor(im.rad.y), length=im.rad.y*2+1))
    if (class(x)=='try-error' | class(y)=='try-error') { 
      return=NA
    } else { 
      xy = expand.grid(x,y)
      r=sqrt(xy[,1]^2+xy[,2]^2)
      #}}}
      #Determine Confidence Radius {{{
      tmp.order<-order(r)
      zvec<-as.numeric(zdist[lim[1]:lim[2],lim[3]:lim[4]])
      zbin<-zvec[tmp.order]
      rcut<-max(abs(r[tmp.order][zbin>max(zdist,na.rm=TRUE)*0.5]))
      #}}}
      #Return FWHM {{{
      return=ceiling(rcut)*2
      #}}}
    }
  } else { 
    return=NA 
  }

}