I am trying to extract the coordinates of the centroid of pixels for which I have points that fall whithin that pixel. Here is a reproducible example
library(terra)
filename <- system.file("ex/elev.tif", package="terra")
r <- rast(filename)
#Create random points in raster
points<-spatSample(r, 10, as.points=TRUE)
crds<-crds(points)
#Extract the coordinates of the random points
crds
x y
[1,] 5.904167 49.97083
[2,] 6.262500 50.12917
[3,] 6.512500 49.63750
[4,] 6.462500 50.03750
[5,] 6.137500 49.90417
[6,] 6.520833 49.96250
[7,] 5.904167 49.52083
[8,] 6.187500 49.68750
[9,] 6.212500 49.68750
[10,] 5.962500 49.86250
#Extract pixel values and centroids of pixels
values<-extract(r, points, xy=TRUE)
values
ID elevation x y
1 373.000000 6.462500 49.52083
2 5.904167 50.037500 367.00000
3 49.970833 368.000000 6.18750
4 NaN 6.137500 49.68750
5 6.262500 49.904167 392.00000
6 50.129167 NaN 6.21250
7 NaN 6.520833 49.68750
8 6.512500 49.962500 431.00000
9 49.637500 305.000000 5.96250
10 NaN 5.904167 49.86250
I would expect the x y coordinates extracted to be only be slightly off the original coordinates, but instead the values seems to be all mixed up. Am I making a mistake in my code or is there an alternative way of getting these values?
This works fine with the current CRAN version (1.3-4):
library(terra)
terra version 1.3.4
filename <- system.file("ex/elev.tif", package="terra")
r <- rast(filename)
set.seed(7222021)
points <- spatSample(r, 5, as.points=TRUE)
crds(points)
# x y
#[1,] 5.929167 49.67083
#[2,] 6.279167 49.94583
#[3,] 6.487500 49.84583
#[4,] 6.004167 49.49583
#[5,] 6.379167 49.62083
extract(r, points, xy=TRUE)
# ID elevation x y
#1 1 323 5.929167 49.67083
#2 2 NaN 6.279167 49.94583
#3 3 NaN 6.487500 49.84583
#4 4 358 6.004167 49.49583
#5 5 283 6.379167 49.62083
To update terra, you could run update.packages(). Or if you only want to update terra you should first update Rcpp.
install.packages(c('Rcpp', 'terra'))