Computes hessian to be used for variance-covariance matrix. The hessian is the outer product of the vector of first partials (see pg 62 of Buckland et al 2002).
flt.var(ddfobj, misc.options)distance sampling object
width-transect width (W); int.range-integration range for observations; showit-0 to 3 controls level of iteration printing; integral.numeric-if TRUE integral is computed numerically rather than analytically
variance-covariance matrix of parameters in the detection function
Buckland et al. 2002