How to query the Google Maps API for geo-referencing using R

georeferencing.R

## 2.2 Georeferecing with Google API
# Has a maximum of 2500 requests per day (error: You have exceeded your daily request quota for this API)
rm(list = ls(all=T))
unique.Geodata <- read.csv('Datasets/unique.Geodata.csv', h=T)
head(unique.Geodata)
dim(unique.Geodata) # 22132    10
str(unique.Geodata)
unique.Geodata$LongitudeDD <- as.character(unique.Geodata$LongitudeDD)
unique.Geodata$LatitudeDD <- as.character(unique.Geodata$LatitudeDD)
unique.Geodata$Geodata <- as.character(unique.Geodata$Geodata)
str(unique.Geodata)
library(sp)
library(raster)
library(XML)
library(dismo)

# Try some names
try(geocode('Malaysia/Malaya; Batu Puteh; '))
try(geocode('Vietnam, Hon Ba'))
try(geocode('Ban-chiou-chian, Che-li Hsien, Yunnan, Jinghong, China, Asia'))
geocode('Che-li Hsien, Yunnan, Jinghong, China, Asia')
geocode("Jardin d'expérience de Collioure, de l'intérieure de l'Afrique, Namibia")
geocode('Jardin d expérience de Collioure, de l intérieure de l Afrique, Namibia')

# Replace coordinates with Google coordinates if accuracy is within uncertainty
uncertainty <- 10000 # in meters (= 10km)

for(j in 1:nrow(unique.Geodata)){
#for(j in 778:nrow(unique.Geodata)){
  Sys.sleep(0.5) # wait 0.5 seconds
  b <- geocode(unique.Geodata$Geodata[j])
  print(j)
  b2 <- subset(b, b$uncertainty == min(b$uncertainty)) # select record with least uncertainty
  if(dim(b2)[1] == 0){
    unique.Geodata[j, 'LatitudeDD'] <- unique.Geodata[j, 'LatitudeDD'] #; print(1)
    unique.Geodata[j, 'LongitudeDD'] <- unique.Geodata[j, 'LongitudeDD'] #; print('a')  
  } else {
    b2 <- b2[1,] # sometimes 2 same minimum values i.e. geocode('Austria,Niederoesterreich,Weinviertel,Katzelsdorf')
    if(b2[, 'uncertainty'] < uncertainty) {
      unique.Geodata[j, 'LatitudeDD'] <- b2[, 'latitude']
      unique.Geodata[j, 'LongitudeDD'] <- b2[, 'longitude']
      unique.Geodata[j, 'coordUncertaintyM'] <- b2[, 'uncertainty']
    } else {
      unique.Geodata[j, 'LatitudeDD'] <- unique.Geodata[j, 'LatitudeDD']
      unique.Geodata[j, 'LongitudeDD'] <- unique.Geodata[j, 'LongitudeDD']
    }
  }
}