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library(dplyr) | |
library(sp) | |
library(rgdal) | |
library(tibble) | |
find_UTM_zone <- function(longitude, latitude) { | |
# Special zones for Svalbard and Norway | |
if (latitude >= 72.0 && latitude < 84.0 ) | |
if (longitude >= 0.0 && longitude < 9.0) | |
return(31); | |
if (longitude >= 9.0 && longitude < 21.0) | |
return(33) | |
if (longitude >= 21.0 && longitude < 33.0) | |
return(35) | |
if (longitude >= 33.0 && longitude < 42.0) | |
return(37) | |
(floor((longitude + 180) / 6) %% 60) + 1 | |
} | |
find_UTM_hemisphere <- function(latitude) { | |
ifelse(latitude > 0, "north", "south") | |
} | |
# returns a DF containing the UTM values, the zone and the hemisphere | |
longlat_to_UTM <- function(long, lat, units = 'm') { | |
df <- data.frame( | |
id = seq_along(long), | |
x = long, | |
y = lat | |
) | |
sp::coordinates(df) <- c("x", "y") | |
hemisphere <- find_UTM_hemisphere(lat) | |
zone <- find_UTM_zone(long, lat) | |
sp::proj4string(df) <- sp::CRS("+init=epsg:4326") | |
CRSstring <- paste0( | |
"+proj=utm +zone=", zone, | |
" +ellps=WGS84", | |
" +", hemisphere, | |
" +units=", units) | |
if (dplyr::n_distinct(CRSstring) > 1L) | |
stop("multiple zone/hemisphere detected") | |
res <- sp::spTransform(df, sp::CRS(CRSstring[1L])) %>% | |
tibble::as_data_frame() %>% | |
dplyr::mutate( | |
zone = zone, | |
hemisphere = hemisphere | |
) | |
res | |
} | |
UTM_to_longlat <- function(utm_df, zone, hemisphere) { | |
CRSstring <- paste0("+proj=utm +zone=", zone, " +", hemisphere) | |
utmcoor <- sp::SpatialPoints(utm_df, proj4string = sp::CRS(CRSstring)) | |
longlatcoor <- sp::spTransform(utmcoor, sp::CRS("+init=epsg:4326")) | |
tibble::as_data_frame(longlatcoor) | |
} |
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