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https://github.com/cran/fields
13 September 2023, 07:07:31 UTC
Revision 8182a9a01e5ac26047a101825b76f85617a37cf8 authored by Doug Nychka on 06 February 2009, 21:36:12 UTC, committed by cran-robot on 06 February 2009, 21:36:12 UTC 
version 5.02
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Tip revision: 8182a9a01e5ac26047a101825b76f85617a37cf8 authored by Doug Nychka on 06 February 2009, 21:36:12 UTC
version 5.02
Tip revision: 8182a9a
poisson.cov.R 
# fields, Tools for spatial data
# Copyright 2004-2007, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html

"poisson.cov" <-
function (x1, x2, eta = 0.2) 
{
    if (missing(x2)) 
        x2 <- x1
#
# dot products of direction cosines  
#
    PP1 <- cbind(cos((x1[, 2] * pi)/180) * cos((x1[, 1] * 
        pi)/180), cos((x1[, 2] * pi)/180) * sin((x1[, 1] * 
        pi)/180), sin((x1[, 2] * pi)/180))
    PP2 <- cbind(cos((x2[, 2] * pi)/180) * cos((x2[, 1] * 
        pi)/180), cos((x2[, 2] * pi)/180) * sin((x2[, 1] * 
        pi)/180), sin((x2[, 2] * pi)/180))
   D  <- (PP1 %*% t(PP2))
con <- (1 - eta^2)^(1.5)
    con/(1 - 2 * eta * D + eta^2)^(1.5)
}
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