Download and georeference photos

Download and georeference photos

Usage

get_photos(
  source,
  outdir = NULL,
  mode = "raw",
  quiet = FALSE,
  overwrite = FALSE
)

Arguments

source

character; url(s) build from find_photos().

outdir

character or NULL; Directory where photos will be saved. Defaults to NULL, in which case the package user overwrite directory (tools::R_user_dir()) is used.

mode

character; One of :

• "raw" : download photos as-is, with no spatial reference.

• "gcp" : download and attach Ground Control Points (GCPs). The photo is georeferenced but not resampled onto a regular grid.

• "warp" : download, georeference, and warp using GDAL. The photo is resampled to a grid, ensuring compatibility with most GIS software.

quiet

logical. If TRUE, suppress progress messages. Default to FALSE.

overwrite

logical. If TRUE, existing files are overwritten. Default to FALSE.

Value

character; filepaths of each photos

Details

Georeferencing performed by "gcp" or "warp" is only a first approximation, based on the scale and orientation metadata provided with the scans. This positioning can be significantly inaccurate. For precise work, users should refine the georeferencing manually in a GIS software. To assist with manual georeferencing, see get_georef_helpers()

The affine transformation is used, which means no geometric deformation is applied beyond shift, rotation, and scale. All georeferenced outputs are written in EPSG:3857 (Web Mercator).

See also

curl::multi_download()

Examples

if (FALSE) { # \dontrun{
library(sf)
library(terra)
x <- read_sf(system.file("extdata/penmarch.shp", package = "happign"))
image_metadata <- find_photos(x, 1969)
tmp <- tempdir()
photo <- get_photos(image_metadata$url[1], tmp)

plot(rast(photo))
} # }