my_raster.tiff file is the PM2.5 concentration in China in 2013.
I've uploaded the data (my_raster.tiff) to Github (https://github.com/lizhiwei1994/example_data/blob/main/my_raster.tiff) in order to reproduce the code.
I want to extract the concentration of PM2.5 at a particular latitude and longitude.
I found the following code on the Internet.
It can batch extract PM2.5 concentration at specific latitude and longitude. For simplicity, I only processed one TIFF image (my_raster.tiff).
The code works fine. But in the output CSV file, my result was repeated 12 times. I think this code has something to do with it: result<-matrix(rep(0,12*n),ncol = n).
I think the original code downloaded from the Internet is set to 12 to deal with a TIFF image containing 12 layers of data. But in my data, my_raster.tiff contains only one layer of data (PM2.5 concentration in 2013).
So my question is if my my_raster.tiff contains a total of 12 years of data from 2013 to 2024, will there be no duplicate value in the result?
# I think there might be something wrong with the code
result<-matrix(rep(0,12*n),ncol = n) #I think this is where the problem lies
Below is the complete code downloaded from the web
install.packages(c("rgdal","raster"))
library(rgdal)
library(raster)
name <- strsplit(getwd(),split="/")
number <- length(name[[1]])
csvname <- paste(as.character(name[[1]][number]),".csv",sep = '')
lst <- list.files(path=getwd(),pattern='tiff$',full.names = T)
n <- length(lst)
data<-data.frame(Lon = 116.3783, Lat = 39.86483)
attach(data)
coordinates(data)<-c("Lon","Lat")
esult<-matrix(rep(0,12*n),ncol = n) #I think this is where the
#problem lies
bio_number<-vector()
for(i in 1:length(lst)){
filename <- strsplit(lst[[i]],split="/")
file<-filename[[1]][length(filename[[1]])]
BIO <- raster(file)
BIO_centroid <- raster::extract(BIO, data, method='simple', buffer=1000, fun=mean, df=TRUE)
bio_number[i]<-strsplit(strsplit(lst[[i]],split="/")[[1]][number+1],split=".tif")[[1]]
result[,i]<-BIO_centroid[,2]
}
colnames(result)<-bio_number
It looks like you make things much more complicated than need be. Here is a general workflow using terra (the replacement for raster).
#files <- list.files(path=getwd(),pattern='tiff$',full.names = T)
files <- c("my_raster.tiff", "my_raster.tiff", "my_raster.tiff")
library(terra)
r <- rast(files)
pts <- data.frame(Lon = 116.3783, Lat = 39.86483)
e <- extract(r, pts)
e
# ID my_raster my_raster my_raster
#1 1 57.80168 57.80168 57.80168
In this case the numbers are the same, because I use the same file three times, but if you use 12 different files you could get 12 different numbers on each row (one row for each point).