Convert seed coordinates between raster index, map, and WGS84 systems

These helpers make it easy to express an existing set of seed coordinates in a different coordinate system. Seeds are accepted when they already contain the target column pair and otherwise are projected using the provided raster.

Usage

as_seeds_rc(seeds, x)

as_seeds_xy(seeds, x)

as_seeds_wgs84(seeds, x)

Arguments

seeds

A data frame, tibble, or matrix that contains one of the column pairs (r, c), (x, y), or (lat, lon).

x

A SpatRaster or in-memory array that supplies the metadata needed to perform conversions. For array inputs, note that the internal coordinate system has its y-axis inverted (increasing upwards) compared to matrix indices (which increase downwards).

Value

A data frame with the target coordinate columns and any additional columns that were present in seeds.

Note

Only rasters with a defined coordinate reference system (CRS) can be transformed to WGS84 coordinates. If the input raster `x` lacks a CRS, attempting to convert to WGS84 will result in an error.

Target systems

as_seeds_rc()

Ensures seeds are expressed in raster row / column indices (r, c).

as_seeds_xy()

Ensures seeds use the raster CRS in map units (x, y).

as_seeds_wgs84()

Ensures seeds are in geographic coordinates (lat, lon) in EPSG:4326.

Examples

if (requireNamespace("terra", quietly = TRUE)) {
    # Load a test Sentinel-2 band
    s2_file <- system.file(
        "demo-geotiff/S2_20LMR_B04_20220630.tif",
        package = "snic"
    )
    s2_rast <- terra::rast(s2_file)

    # Create some test coordinates in pixel space
    seeds_rc <- data.frame(r = c(10, 20, 30), c = c(15, 25, 35))

    # Convert to map coordinates (x,y)
    seeds_xy <- as_seeds_xy(seeds_rc, s2_rast)

    # Convert to geographic coordinates (lat,lon)
    seeds_wgs84 <- as_seeds_wgs84(seeds_rc, s2_rast)
}