Download SRTM elevation maps locally and load them into R. The files correspond to the SRTM3 V2.1 maps.
Install the SRTM package from Github:
require(devtools)
install_github('jsga/SRTM_maps_in_R')
Load the library, download the elevation maps around mount Everest and plot them:
library(SRTM)
everest = get_srtm_raster(lon = 86.922623, lat = 27.986065 , n=1, exdir_srtm_hgt = "data-raw/SRTM_maps_everest")
# Takes a while the first time
# See downloaded .hgt files in data-raw/SRTM_maps_everest
raster::plot(everest)
The number of tiles downloaded depend on the option n. For_n=0_ a single map tile is downloaded. For n=1, the center tile is downloaded plus each 1 surrounding tile. So, 9 in total. For n=2 the center tile plus 2 surrounding tiles, meaning 25 in total. In general, (2*n+1)^2 tiles are downloaded. The graph below shows the output for n=1 and n=2:
The package also contains a dataset that has saves the location of each tile on the server:
head(SRTM::SRTM_files_info)
full_path name_file NS coorNS WE coorWE
1 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E006.hgt.zip N00E006 N 0 E 6
2 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E009.hgt.zip N00E009 N 0 E 9
3 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E010.hgt.zip N00E010 N 0 E 10
4 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E011.hgt.zip N00E011 N 0 E 11
5 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E012.hgt.zip N00E012 N 0 E 12
6 https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E013.hgt.zip N00E013 N 0 E 13
The dataset has been gathered by parsing web server, using this script.
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