% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/estimateN.r
\name{estimateN}
\alias{estimateN}
\title{Abundance point estimates}
\usage{
estimateN(object, area = NULL, propUnitSurveyed = 1)
}
\arguments{
\item{object}{An Rdistance model frame or fitted distance function,
normally produced by a call to \code{\link{dfuncEstim}}.}

\item{area}{A scalar containing the total area of inference. Usually, this is 
study area size.  If \code{area} is NULL (the default), 
\code{area} will be set to 1 square unit of the output units and density estimates
will be produced. 
If \code{area} is not NULL, it must have measurement units 
assigned by the \code{units} package. 
The units on \code{area} must be convertible
to squared output units. Units 
on \code{area} must be two-dimensional. 
For example, if output units are "foo", 
units on area must be convertible to "foo^2" by the \code{units}
package. Units of "km^2", "cm^2", "ha", "m^2", "acre", "mi^2", and several
others are acceptable.}

\item{propUnitSurveyed}{A scalar or vector of real numbers between 0 and 1.
The proportion of the default sampling unit that 
  was surveyed.  If both sides of line transects were observed, 
  \code{propUnitSurveyed}
  = 1.  If only a single side of line transects were observed, set 
  \code{propUnitSurveyed} = 0.5. For point transects, this should be set to 
  the proportion of each circle that was observed. Length must either be
  1 or the total number of transects in \code{x}.}
}
\value{
A list containing the following components:

   \item{density}{Estimated density in the surveyed area.}
   
   \item{abundance}{Estimated abundance on the study area. Equals density if 
   area is not specified.}
   
   \item{n.groups}{The number of detected groups (not individuals, unless all group sizes = 1).}
   
   \item{n.seen}{The number of individuals (sum of group sizes).}
   
   \item{area}{Total area of inference. Study area size}
   
   \item{surveyedUnits}{Number of surveyed sites.  This is total transect length
   for line-transects or number of points for point-transects. This total transect
   length does not include transects with missing lengths.}
   
   \item{propUnitSurveyed}{Proportion of the standard survey unit
   that was observed}
   
   \item{avg.group.size}{Average group size on non-NA transects}
   
   \item{w}{Strip width. }
   
   \item{pDetection}{Probability of detection.}
   
For line-transects that do not involve covariates, object$density  
is object$n.seen / (2 * propUnitSurveyed * object$w * object$pDetection * object$surveyedUnits)
}
\description{
Estimate abundance from an Rdistance fitted model. 
This function is called internally by \code{abundEstim}.  Most users will call 
\code{abundEstim} to estimate abundance unless they are running simulations or 
bootstrapping.
}
\details{
The abundance estimate for line-transect surveys (if no covariates
   are included in the detection function and both sides of the transect 
   are observed) is 
   \deqn{N =\frac{n(A)}{2(ESW)(L)}}{%
         N = n*A / (2*ESW*L)} 
   where \emph{n} is total number of sighted individuals 
  (i.e., \code{sum(groupSizes(dfunc))}), \emph{L} is the total length of 
  surveyed transect (i.e., \code{sum(effort(dfunc))}),
  and \emph{ESW} is effective strip width
  computed from the estimated distance function (i.e., \code{ESW(dfunc)}).
  If only one side of transects were observed, the "2" in the denominator 
  is not present (or, replaced with a "1"). 
  
  The abundance estimate for point transect surveys (if no covariates are
  included) is 
   \deqn{N =\frac{n(A)}{\pi(ESR^2)(P)}}{%
         N = n*A / ((3.1415)*ESR^2*(P))} 
   where \emph{n} is total number of sighted individuals (i.e., \code{sum(groupSizes(dfunc))}),
   \emph{P} is the total number of surveyed points (i.e., \code{sum(effort(dfunc))}), 
   and \emph{ESR} is effective search radius 
   computed from the estimated distance function (i.e., \code{ESR(dfunc)}).

 This routine, \code{abundEstim}, estimates abundance on the 
 entire study area.  Site-specific density estimates 
 are computed by 
 \code{predict(x, type = "density")}, which returns a 
 tibble containing density and abundance on the area surveyed by every
 transect.
}
\seealso{
\code{\link{dfuncEstim}}, \code{\link{abundEstim}}
}
