covf = new(covf_mat25ang)This is the standard Matern covariance function with a power transformation
which has form
$$c(x_1,x_2) = (1+ |h| + h^2/3) \exp(-|h|) $$
where $$h = \sqrt{(\sin(x_1)-\sin(x_2))^2/\rho_s +
(\cos(x_1)-\cos(x_2))^2/\rho_c}.$$
hyp is a two dimensional vector with
\(\rho_s\)=exp(2*hyp[0]) and \(\rho_c\)=exp(2*hyp[1]).
See also
base class: covf