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Associate vector coordinates with a raster surface for Unity import

Source: R/associate_coordinates.R
associate_coordinates.Rd

Unity uses a left-handed coordinate system, which is effectively "flipped" from our normal way of thinking about spatial coordinate systems. It also can only import terrain as square tiles of side 2^x + 1, for x between 5 and 12. As a result, importing objects into a Unity scene so that they align with terrain surfaces is trickier than you'd expect. This function "associates" the XY coordinates from some sf object, likely a point data set, with some raster object.

Usage

associate_coordinates(object, raster, side_length = 4097)

Arguments

object

The sf object to take coordinates from. The object will be reprojected (via sf::st_transform) to align with raster.

raster

A raster or file path to a raster to associate coordinates with. Note that different rasters will produce different coordinate outputs; you should run this function with the same raster you plan on bringing into Unity. Any file or object that can be read via terra::rast can be used.

side_length

The side length of terrain tiles, in map units, you intend to bring into Unity. Must be a value equal to 2^x + 1, for x between 5 and 12. All functions in the unifir family default to 4097.

Value

A data.frame with two columns, X and Y, representing the re-aligned coordinates. If object is point data (or anything object that sf::st_coordinates returns a single row for each row of), these rows will be in the same order as object (and so can be appended via cbind).

Examples

if (FALSE) {
if (!isTRUE(as.logical(Sys.getenv("CI")))) {
  simulated_data <- data.frame(
    id = seq(1, 100, 1),
    lat = runif(100, 44.04905, 44.17609),
    lng = runif(100, -74.01188, -73.83493)
  )
  simulated_data <- sf::st_as_sf(
    simulated_data,
    coords = c("lng", "lat"),
    crs = 4326
   )
  output_files <- terrainr::get_tiles(simulated_data)
  temptiff <- tempfile(fileext = ".tif")
  terrainr::merge_rasters(output_files["elevation"][[1]], temptiff)
  associate_coordinates(simulated_data, temptiff)
}
}