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Read the camera a frame's PAT-B file names

Source: R/fly_camera_patb.R
fly_camera_patb.Rd

Downloads and parses the per-frame georeferencing files the BC Data Catalogue publishes through patb_georef_url, and attaches the camera identity they carry to the photo centroids. fly_footprint() then sizes those frames from the named camera instead of refusing them, which needs no DEM.

Usage

fly_camera_patb(
  photos_sf,
  dest_dir = tempfile("fly_patb"),
  overwrite = FALSE,
  quiet = FALSE
)

Arguments

photos_sf

An sf object with airphoto metadata, typically from the BC Data Catalogue centroid layer. Must contain patb_georef_url, and film_roll and frame_number or airp_id to join on.

dest_dir

Directory to cache the downloaded archives in. Defaults to a session temporary directory; give it a real path to keep them between runs.

overwrite

If FALSE (default), archives already in dest_dir are reused rather than re-downloaded.

quiet

Suppress the per-archive progress messages.

Value

photos_sf with four columns added, all NA where nothing resolved:

camera_serial

the camera or lens serial the file publishes

camera_name

the model string the file publishes, where it has one

patb_gsd

ground sample distance in centimetres, matching the catalogue's own units. The catalogue's ground_sample_distance is 0 for whole years of digital imagery, and this is where the number is

patb_source

the archive each row was resolved from

Details

This is the only function in the package that reaches the network on the sizing path. fly_footprint() takes the columns it produces and never fetches anything itself, so a batch can be resolved once and reused.

Three file schemas are in circulation and they are dispatched on the columns present rather than the file extension, because the extension does not identify them. Two of the archives referenced by the frames this exists for are 404s served as HTML under a .csv name; those frames are reported as unresolved, by a message naming the archive rather than by an error, so one missing file does not cost a batch its other frames.

A serial that the shipped camera table does not recognise is refused rather than resolved from the model string beside it. One published archive labels both its cameras UltraCam XP while one of them is an UltraCam X, a 20% difference in ground width — so the model string is read only where the file carries no serial at all. See inst/notes/camera-formats.md.

Examples

centroids <- sf::st_read(system.file("testdata/photo_centroids_digital.gpkg",
                                     package = "fly"), quiet = TRUE)

# Copy the bundled archives into a scratch directory, so this runs offline and
# writes nothing into the installed package
cache <- file.path(tempdir(), "patb")
dir.create(cache, showWarnings = FALSE)
file.copy(list.files(system.file("testdata", "patb", package = "fly"),
                     full.names = TRUE), cache)
#> [1] TRUE TRUE TRUE TRUE

resolved <- fly_camera_patb(centroids, dest_dir = cache)
#> Downloaded 2 of 2 files
#> d_003_fi_13_georef.zip: 18 of 18 frames resolved
#> d_005_emn_19_georef.zip: 6 of 6 frames resolved
table(resolved$camera_serial, useNA = "ifany")
#> 
#>   121201 22814295 
#>       18        6 

# `fly_footprint()` picks the columns up from here. These frames also carry a
# calibration report, which wins; drop it and the PAT-B serial sizes them.
resolved$camera_calibration_url <- NA_character_
fp <- fly_footprint(resolved)
unique(fp$width_source)
#> [1] "patb_serial=121201"   "patb_serial=22814295"