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dnanto/geomid.R

Created June 25, 2020 18:14
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  1. dnanto created this gist Jun 25, 2020.
    23 changes: 23 additions & 0 deletions geomid.R
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    library(tidyverse)

    geomid <- function(lat, lon)
    {
    # http://www.geomidpoint.com/calculation.html
    lat <- lat * pi / 180
    lon <- lon * pi / 180
    x <- mean(sum(cos(lat) * cos(lon)))
    y <- mean(sum(cos(lat) * sin(lon)))
    z <- mean(sum(sin(lat)))
    lat <- atan2(y, x)
    hyp <- sqrt(x * x + y * y)
    lon <- atan2(z, hyp)
    c(lat = lat * 180 / pi, lon = lon * 180 / pi)
    }

    # calculate the geographic midpoint for each county in the US
    map_data("county") %>%
    mutate(polyname = str_c(region, subregion, sep = ",")) %>%
    group_by(polyname) %>%
    group_modify(~ {
    as.data.frame(t(geomid(.x$lat, .x$long)))
    })