Created
November 27, 2015 18:22
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R-script voor het downloaden en georefereren van een OpenStreetMap tile
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setwd("D:/temp") | |
# Functie om op basis van latitude, longitude en zoomniveau de bijbehorende OpenStreetMap tile te berekenen | |
# Zie http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames | |
deg2num <- function(lat_deg, lon_deg, zoom) { | |
lat_rad <- lat_deg * pi /180 | |
n <- 2.0 ^ zoom | |
xtile <- floor((lon_deg + 180.0) / 360.0 * n) | |
ytile = floor((1.0 - log(tan(lat_rad) + (1 / cos(lat_rad))) / pi) / 2.0 * n) | |
return (c(xtile, ytile)) | |
} | |
# Martinitoren: | |
# latitude = 53.21921 | |
# longitude = 6.568 | |
# zoomniveau = 18 | |
lat <- 53.21921 | |
lon <- 6.568 | |
zoom <- 18 | |
tile <- deg2num(lat, lon, zoom) | |
x <- tile[1] | |
y <- tile[2] | |
# Download tile | |
# URL template: http://[abc].tile.openstreetmap.org/zoom/x/y.png | |
url <- paste0(paste("http://a.tile.openstreetmap.org", zoom, x, y, sep="/"), ".png") | |
download.file(url, destfile = basename(url), mode = "wb") | |
# Genereer een World-file (*.PGW) voor het zojuist gedownloade PNG-bestand | |
# Bereken eerst de bounding box van de tile | |
tile2lon <- function(xtile, zoom) { | |
return (xtile / 2.0 ^ zoom * 360.0 - 180.0); | |
} | |
tile2lat <- function(ytile, zoom) { | |
n <- pi - ytile / 2.0 ^ zoom * 2 * pi; | |
return (atan(sinh(n)) * 180 / pi); | |
} | |
boundingBox <- function(xtile, ytile, zoom){ | |
north <- tile2lat(ytile, zoom); | |
south <- tile2lat(ytile + 1, zoom); | |
west <- tile2lon(xtile, zoom); | |
east <- tile2lon(xtile + 1, zoom); | |
return( c(north, south, east, west)) | |
} | |
bb <- boundingBox(x, y, zoom) | |
# Maak het PGW-bestand aan | |
TileWidthDeg <- bb[3] - bb[4] | |
TileHeightDeg <- bb[1] - bb[2] | |
fileConn<-file(paste0(y, ".pgw")) | |
writeLines(c(as.character(TileWidthDeg / 256), "0.0", "0.0", as.character(-1 * TileHeightDeg / 256), as.character(bb[4]), as.character(bb[1])), fileConn) | |
close(fileConn) |
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