New vignette

R/dist_pres_vs_bg.R

@@ -37,8 +37,11 @@ dist_pres_vs_bg <- function(
     if (inherits(.data, "sf")) {
       .data <- .data %>% sf::st_drop_geometry()
     }
-    # subset to only columns which are numeric
+    # subset to only columns which are numeric and check for NAs
     num_vars <- names(.data)[!names(.data) %in% .col]
+    if (any(is.na(.data[num_vars]))) {
+      stop("NAs in the dataframe")
+    }
     dist_vec <- numeric()
     for (i_var in num_vars) {
       vals_list <- list(

R/thin_by_cell.R

@@ -6,6 +6,9 @@
 #' Further thinning can be achieved by aggregating cells in the raster
 #' before thinning, as achieved by setting `agg_fact` > 1 (aggregation works in a
 #' manner equivalent to [terra::aggregate()]).
+#' Note that if `data` is an `sf` object, the function will transform the coordinates
+#' to the same projection as the `raster` (recommended); if `data` is a data.frame, it is up
+#' to the user to ensure that the coordinates are in the correct units.
 #'
 #' @param data An [`sf::sf`] data frame, or a data frame with coordinate variables.
 #' These can be defined in `coords`, unless they have standard names
@@ -32,10 +35,11 @@
       "use `thin_by_cell_time()`"
     )
   }
   if (inherits(raster, "stars")) raster <- as(raster, "SpatRaster")
   # add type checks for these parameters
   return_sf <- FALSE # flag whether we need to return an sf object
   if (inherits(data, "sf")) {
+    data <- data %>% sf::st_transform(terra::crs(raster))
     if (all(c("X", "Y") %in% names(data))) {
       if (!all(data[, c("X", "Y")] %>% sf::st_drop_geometry() %>% as.matrix() == sf::st_coordinates(data)) |
         any(is.na(data[, c("X", "Y")]))) {

R/thin_by_cell_time.R

@@ -8,6 +8,9 @@
 #' Further spatial thinning can be achieved by aggregating cells in the raster
 #' before thinning, as achieved by setting `agg_fact` > 1 (aggregation works in a
 #' manner equivalent to [terra::aggregate()]).
+#' Note that if `data` is an `sf` object, the function will transform the coordinates
+#' to the same projection as the `raster` (recommended); if `data` is a data.frame, it is up
+#' to the user to ensure that the coordinates are in the correct units.
 #'
 #' @param data An [`sf::sf`] data frame, or a data frame with coordinate variables.
 #' These can be defined in `coords`, unless they have standard names
@@ -49,14 +52,14 @@ thin_by_cell_time <- function(data, raster, coords = NULL, time_col = "time",
   if (inherits(raster, "SpatRasterDataset")) {
     raster <- raster[[1]]
   }
-  
+
   if(inherits(raster, "stars")) {
     d <- stars::st_dimensions(raster)
     time <- stars::st_get_dimension_values(raster, "time")
     raster <- as(raster, "SpatRaster")
     terra::time(raster, tstep = d$time$refsys) <- time
   }
-  
+
   time_steps <- terra::time(raster)
 
   if (any(is.na(time_steps))) {

R/thin_by_dist.R

@@ -19,13 +19,15 @@
 #'  `c("longitude", "latitude")`, or `c("lon", "lat")`
 #' @param dist_min Minimum distance between points (in units appropriate for
 #' the projection, or meters for lonlat data).
+#' @param dist_method method to compute distance, either "euclidean" or "great_circle".
+#' Defaults to "great_circle", which is more accurate but takes slightly longer.
 #' @returns An object of class [`sf::sf`] or [`data.frame`], the same as "data".
 #' @export
 #' @importFrom rlang :=
 
 # This code is an adaptation of spThin to work on sf objects
 
-thin_by_dist <- function(data, dist_min, coords = NULL) {
+thin_by_dist <- function(data, dist_min, coords = NULL, dist_method = c("great_circle", "euclidean")) {
   return_dataframe <-
     FALSE # flag whether we need to return a data.frame
   if (!inherits(data, "sf")) {
@@ -35,6 +37,14 @@ thin_by_dist <- function(data, dist_min, coords = NULL) {
     return_dataframe <- TRUE
   }
 
+  #use the proper method of distance calculation by changing projection if necessary
+  dist_method <- match.arg(dist_method)
+  if (dist_method == "great_circle") {
+    # store the original projection
+    original_crs <- sf::st_crs(data)
+    data <- sf::st_transform(data, 4326)
+  }
+
   # compute distances with sf, using the appropriate units for the projection
   dist_mat <- sf::st_distance(data)
   units(dist_min) <- units(dist_mat)
@@ -85,6 +95,11 @@ thin_by_dist <- function(data, dist_min, coords = NULL) {
 
   ## Subset the original dataset
   thinned_points <- data[points_to_keep, ]
+  # if we used great circle distances, we need to transform back
+  if (dist_method == "great_circle") {
+    thinned_points <- sf::st_transform(thinned_points, original_crs)
+  }
+
   if (return_dataframe) {
     thinned_points <- thinned_points %>%
       dplyr::bind_cols(sf::st_coordinates(thinned_points)) %>% # re-add coordinates

R/thin_by_dist_time.R

@@ -26,14 +26,16 @@
 #' @param dist_min Minimum distance between points (in units appropriate for
 #' the projection, or meters for lonlat data).
 #' @param interval_min Minimum time interval between points, in days.
+#' @param dist_method method to compute distance, either "euclidean" or "great_circle".
+#' Defaults to "great_circle", which is more accurate but takes slightly longer.
 #' @returns An object of class [`sf::sf`] or [`data.frame`], the same as "data".
 #' @export
 #' @importFrom rlang :=
 
 # This code is an adaptation of spThin to work on sf objects
 
 thin_by_dist_time <- function(data, dist_min, interval_min, coords = NULL,
-                              time_col = "time", lubridate_fun = c) {
+                              time_col = "time", lubridate_fun = c, dist_method = c("great_circle", "euclidean")) {
   return_dataframe <-
     FALSE # flag whether we need to return a data.frame
   # cast to sf if needed
@@ -44,6 +46,14 @@ thin_by_dist_time <- function(data, dist_min, interval_min, coords = NULL,
     return_dataframe <- TRUE
   }
 
+  #use the proper method of distance calculation by changing projection if necessary
+  dist_method <- match.arg(dist_method)
+  if (dist_method == "great_circle") {
+    # store the original projection
+    original_crs <- sf::st_crs(data)
+    data <- sf::st_transform(data, 4326)
+  }
+
   # create a vector of times formatted as proper dates
   time_lub <- data[, time_col] %>%
     as.data.frame() %>%
@@ -108,6 +118,12 @@ thin_by_dist_time <- function(data, dist_min, interval_min, coords = NULL,
 
   ## Subset the original dataset
   thinned_points <- data[points_to_keep, ]
+
+  # if we used great circle distances, we need to transform back
+  if (dist_method == "great_circle") {
+    thinned_points <- sf::st_transform(thinned_points, original_crs)
+  }
+
   if (return_dataframe) {
     thinned_points <- thinned_points %>%
       dplyr::bind_cols(sf::st_coordinates(thinned_points)) %>% # re-add coordinates

data-raw/projections.Rmd

@@ -0,0 +1,133 @@
+---
+title: "Projecting your map"
+author: "Andrea"
+date: "2024-11-22"
+output: html_document
+---
+
+```{r setup, include=FALSE}
+knitr::opts_chunk$set(echo = TRUE)
+```
+
+## Map projections in R
+
+We start with a raster object that has a geographic coordinate reference system (CRS) and we want to project it to a different CRS. We will use the `terra` package to do this. As an example, we will use a map of the Iberian peninsula:
+
+
+```{r}
+library(pastclim)
+download_dataset(dataset = "WorldClim_2.1_10m")
+land_mask <-
+  get_land_mask(time_ce = 1985, dataset = "WorldClim_2.1_10m")
+
+# Iberia peninsula extension
+iberia_poly <-
+  terra::vect(
+    "POLYGON((-9.8 43.3,-7.8 44.1,-2.0 43.7,3.6 42.5,3.8 41.5,1.3 40.8,0.3 39.5,
+     0.9 38.6,-0.4 37.5,-1.6 36.7,-2.3 36.3,-4.1 36.4,-4.5 36.4,-5.0 36.1,
+    -5.6 36.0,-6.3 36.0,-7.1 36.9,-9.5 36.6,-9.4 38.0,-10.6 38.9,-9.5 40.8,
+    -9.8 43.3))"
+  )
+
+crs(iberia_poly) <- "+proj=longlat"
+
+# crop the extent
+land_mask <- crop(land_mask, iberia_poly)
+land_mask <- mask(land_mask, iberia_poly)
+```
+
+We plot it with `tidyterra`:
+
+```{r}
+library(tidyterra)
+library(ggplot2)
+ggplot() +
+  geom_spatraster(data = land_mask, aes(fill = land_mask_1985))
+```
+Now we project it. To define our projection we use a proj4 string, which provides information
+on the type of projection, its parameters and the units of distance in which the new coordinates
+will be expressed. we can use the website `projectionwizard.org` (https://link.springer.com/chapter/10.1007/978-3-319-51835-0_9) to find an appropriate equal
+area projection for any region, and obtain its associated proj4 string.
+In this case, we will use a Alberts Equal Area Conic projection centered on the Iberian peninsula. The proj4 string for this projection is:
+```{r}
+iberia_proj4 <- "+proj=aea +lon_0=-4.0429687 +lat_1=36.7790694 +lat_2=42.6258819 +lat_0=39.7024757 +datum=WGS84 +units=km +no_defs"
+```
+Note that we set the units to km so that have smaller numbers in the new axes.
+
+For rasters (maps), we use the `terra` function `project` to change the CRS. We pass the raster object and the proj4 string as arguments:
+```{r}
+land_mask_proj <- terra::project(land_mask, y = iberia_proj4)
+```
+
+And replot it:
+```{r}
+ggplot() +
+  geom_spatraster(data = land_mask_proj, aes(fill = land_mask_1985))
+```
+Note that the coordinate system has now changed. We can get the true coordinates using the terra::plot function:
+```{r}
+terra::plot(land_mask_proj)
+
+```
+
+We now need to bring in some points. they come in as lat long, so we use the appropriate proj4 string
+for raw coordinates.
+```{r}
+library(tidysdm)
+library(sf)
+data(lacerta)
+lacerta <- st_as_sf(lacerta, coords = c("longitude", "latitude"))
+st_crs(lacerta) <- "+proj=longlat"
+  #4326
+```
+
+Let's inspect the object:
+```{r}
+lacerta
+```
+We can see in the `geometry` column that are coordinates are in arc-degrees long and lat.
+
+Now we project them to the same CRS as the raster, using the appropriate `sf` function
+to project points:
+```{r}
+lacerta_proj <- st_transform(lacerta, iberia_proj4)
+```
+
+```{r}
+lacerta_proj
+```
+Now the coordinates are in kilometers on the new axes.
+
+Plot the projected points on top of the project map:
+```{r}
+ggplot() +
+  geom_spatraster(data = land_mask_proj, aes(fill = land_mask_1985)) +
+  geom_sf(data = lacerta_proj) + guides(fill="none")
+```
+
+The next step is to project the environemntal variables (layers of a raster). First we
+extract the unprojected layers from `pastclim`
+```{r}
+download_dataset("WorldClim_2.1_10m")
+climate_vars <- get_vars_for_dataset("WorldClim_2.1_10m")
+climate_present <- pastclim::region_slice(
+  time_ce = 1985,
+  bio_variables = climate_vars,
+  data = "WorldClim_2.1_10m",
+  crop = iberia_poly
+)
+```
+And now we project them
+```{r}
+climate_present_proj <- terra::project(climate_present, y = iberia_proj4)
+```
+
+Let's plot a layer with the points on top:
+```{r}
+ggplot() +
+  geom_spatraster(data = climate_present_proj, aes(fill = bio01)) +
+  geom_sf(data = lacerta_proj) + guides(fill="none") +
+  scale_fill_gradientn(colors = terrain.colors(7), na.value = "transparent") 
+```
+
+

inst/WORDLIST

@@ -1,8 +1,10 @@
+Albers
 BCI
 Babak
 BlockCV
 Breugel
 CMD
+CRS
 DALEX
 Ecography
 Ecol
@@ -79,6 +81,7 @@ lacertidae
 lat
 lh
 lon
+longlat
 lonlat
 lqpht
 lubridate
@@ -99,6 +102,7 @@ pearson
 pred
 prepping
 prob
+proj
 pseudoabsence
 pseudoabsences
 quasiquotation

tests/testthat/test_dist_pres_vs_bg.R

@@ -0,0 +1,18 @@
+test_that("NAs in dataframe", {
+  # create dataframe with NAs
+    test_dataset <- tibble(
+      class = factor(c("presence", "presence", "presence", "presence", "presence", 
+                          "absence", "absence", "absence", "absence", "absence")),
+      cld6190_ann = c(76, 76, 57, 57, 57, 46, 74, 74, NA, 50),
+      dtr6190_ann = c(104, 104, 114, 112, 113, 143, 93, 93, NA, 161),
+      frs6190_ann = c(2, 2, 1, 3, 3, 112, 0, 0, NA, 133),
+      h_dem = c(121, 121, 211, 363, 303, 1040, 134, 63, NA, 3624)
+    )
+
+    # compute differences between presence and background 
+    expect_error(test_dataset %>% dist_pres_vs_bg(class), 
+                 "NAs in the dataframe")
+})
+
+
+