rparsingr-rasterterra

How to download and save multiple GeoTiff files using a for loop?

I'm trying to download and parse GeoTiff files and extract alphanumeric data from them. The files are provided here:

https://www.wpc.ncep.noaa.gov/heatrisk/data.html

The files are categorical projections of heat risk (e.g., "High", "Very High", etc.) at various California substate geographies. The data I want are the projections and geo IDs (e.g., county names) associated with each projection, not raster data (for now).

(Note: the .kml files provided on the data page are empty, per correspondence with NWS.)

Downloading the .tif files

This code appears to work:

#Load Packages
#install.packages("raster")
#install.packages("terra")
#install.packages("vapour")

library(raster)
library(httr)
library(terra)


#Read In GeoTiff Files

#Base URL
base_url <- https://www.wpc.ncep.noaa.gov/heatrisk/data/

#Function to Read in Files
download_heatrisk_geotiff <- function(day_number) {
  url <- paste0(base_url, "?day=", day_number)
  response <- GET(url)
  
  if (status_code(response) == 200) {
    # Parse the TIFF content
    tif_content <- content(response, "text")
    
    # Save KML content to a file
    writeLines(tif_content, paste0(getwd(), "/data/HeatRisk_", day_number, "_Mercator.tif"))
    cat(paste0("Downloaded HeatRisk_", day_number, "_Mercator.tif\n"))
  } else {
    cat(paste0("Error downloading HeatRisk_", day_number, "_Mercator.tif\n"))
  }
}

# Download .tif files for individual days
for (day in 1:7) {
  download_heatrisk_geotiff(day)
}

Image of downloaded files

It's not clear that the data I want is in the downloaded files. Screenshot of downloaded .tif files

Extracting Data

#Extract Data
geotiff_file <- raster(paste0(getwd(), "/data/HeatRisk_", day_number, "_Mercator.tif"))
geotiff_file2 <- terra::readValues(paste0(getwd(), "/data/HeatRisk_", day_number, "_Mercator.tif"))
geotiff_file3 <- vapour::vapour_read_raster(paste0(getwd(), "/data/HeatRisk_", day_number, "_Mercator.tif"))

I've already consulted these pages:

Thanks!

Solution

  • You have made two assumptions about the data you have linked to that are incorrect:

    1. The data are not at "California substate geographies" level, they are for the entire US.
    2. The data do not contain county names, just values from 0 - 4 representing heat risk and NA

    Here is a workflow to at least get you started. It involves downloading the relevant .tif files and writing them to a directory. If you do need the data at substate level and you cannot find a source, you can post a new question asking how to create these data using the data in this example.

    library(terra)
library(httr)

#Base URL
base_url <- "https://www.wpc.ncep.noaa.gov/heatrisk/data/"
  
#Function to Read in Files
download_heatrisk_geotiff <- function(day_number) {
    url <- paste0(base_url, "HeatRisk_", 1, "_Mercator.tif")
    response <- GET(url)
    
    if (status_code(response) == 200) {
      
      r <- rast(response$url)
      writeRaster(r, paste0(getwd(), "/data/HeatRisk_", day_number, "_Mercator.tif"),
                  overwrite = TRUE)
      
      cat(paste0("Downloaded HeatRisk_", day_number, "_Mercator.tif\n"))
      
    } else {
      
      cat(paste0("Error downloading HeatRisk_", day_number, "_Mercator.tif\n"))
      
    }
  }

# Download .tif files for individual days
for (day in 1:7) {
  
  download_heatrisk_geotiff(day)
  
}

# Load raster from directory
geotiff_file <- rast(paste0(getwd(), "/data/HeatRisk_", 1, "_Mercator.tif"))

# Returin metadata
geotiff_file
# class       : SpatRaster 
# dimensions  : 1672, 2866, 1  (nrow, ncol, nlyr)
# resolution  : 2539.703, 2539.703  (x, y)
# extent      : -14326022, -7047233, 2475760, 6722144  (xmin, xmax, ymin, ymax)
# coord. ref. : WGS 84 / Pseudo-Mercator (EPSG:3857) 
# source      : HeatRisk_1_Mercator.tif 
# color table : 1 
# name        : HeatRisk_1_Mercator 
# min value   :                   0 
# max value   :                   4