Skip to contents

Fetch a DEM cropped to an AOI

Source: R/fl_dem_aoi.R
fl_dem_aoi.Rd

Returns a SpatRaster of elevation cropped to a buffered AOI. Source is a local file, an HTTP COG (/vsicurl/), or an S3 COG (/vsis3/). Defaults to MRDEM-30 — NRCan's Medium-Resolution Digital Elevation Model (30 m, all of Canada, public S3, no auth) — the source-of-truth choice for watershed-scale BC floodplain work as decided in rtj/docs/dem-sources.md.

Usage

fl_dem_aoi(aoi, source = NULL, buffer = 2000, target_crs = NULL)

Arguments

aoi

An sf or sfc object — polygon, lines, or points. Buffered by buffer (via sf::st_buffer()) before crop. To crop tightly along a stream corridor (memory-efficient when the watershed-scale AOI has sparse stream coverage), pass the streams sf here rather than the full WSG polygon.

source

Character. Path or URL for the source raster. NULL (default) uses MRDEM-30 DTM via /vsicurl/. Local file paths, /vsicurl/https://... URLs, and /vsis3/... S3 paths all work — terra::rast() handles them identically.

buffer

Numeric. Distance in metres to buffer aoi before crop. Default 2000.

target_crs

CRS spec recognised by sf::st_crs() (EPSG code, WKT, PROJ string, or crs object). NULL (default) returns the raster in the input AOI's CRS. Reprojection happens after crop, never before — the 84 GB MRDEM COG must not be reprojected as a whole.

Value

A SpatRaster cropped to the buffered AOI extent, projected to target_crs if it differs from the source raster's CRS.

Details

MRDEM-30 (s3://canelevation-dem/mrdem-30/mrdem-30-dtm.tif) is a single 84 GB Cloud-Optimized GeoTIFF in EPSG:3979 covering all of Canada. The /vsicurl/ access pattern range-reads only the bytes intersecting the AOI, so total bandwidth scales with AOI size, not the COG size.

For sub-10 m riparian-scale work where lidar coverage exists, query the stac-dem-bc STAC catalog and pass an item's COG URL as source. See the example below.

See also

fl_valley_confine()

Examples

aoi <- sf::st_read(
  system.file("testdata/streams.gpkg", package = "flooded"),
  quiet = TRUE
)

# Local file (any path or URL works the same way)
dem <- fl_dem_aoi(
  aoi,
  source = system.file("testdata/dem.tif", package = "flooded"),
  buffer = 200
)
terra::plot(dem)


if (FALSE) { # \dontrun{
# Default: MRDEM-30 DTM via /vsicurl/ — fetched lazily from NRCan S3
dem <- fl_dem_aoi(aoi, buffer = 2000)
terra::plot(dem, main = "MRDEM-30 over AOI")

# LidarBC via stac-dem-bc — sub-10 m where lidar coverage exists
bbox_4326 <- sf::st_bbox(sf::st_transform(aoi, 4326))
items <- rstac::stac("https://images.a11s.one/") |>
  rstac::stac_search(
    collections = "stac-dem-bc",
    bbox = unname(bbox_4326)
  ) |>
  rstac::post_request() |>
  rstac::items_fetch()
if (length(items$features) > 0L) {
  cog <- paste0("/vsicurl/", items$features[[1]]$assets$image$href)
  dem_lidar <- fl_dem_aoi(aoi, source = cog, buffer = 100)
}
} # }