Changes in version 0.1.0                        

Initial release. TIFF/COG metadata scanning and tile decoding from R via
Rust, without GDAL or Python.

Core functions

  - tiff_refs() scans TIFF/COG files and returns a data.frame of tile
    byte-range references (path, IFD, tile col/row, offset, length,
    dimensions, dtype, compression, CRS EPSG). Accepts S3, GCS, Azure,
    HTTP/HTTPS, and local file paths. Multiple files are scanned
    sequentially (concurrent scanning is a planned enhancement).

  - tiff_tile() fetches and decodes a single tile from a TIFF/COG,
    returning decoded pixel values as a numeric vector with dimension
    and dtype metadata. Handles deflate and JPEG compression natively
    via async-tiff.

  - tiff_tiles() fetches multiple tiles from the same file in a single
    call, opening the TIFF once and reusing the metadata and connection.
    More efficient than calling tiff_tile() in a loop.

  - tile_to_array() converts a tile result to an R matrix (single band)
    or 3D array (multi-band).

Reference store output

  - refs_to_kerchunk() converts a refs data.frame to Kerchunk V1 JSON,
    suitable for consumption by xarray, zarr-python, or (in future)
    GDAL's Zarr driver. Handles compressor serialization (deflate →
    zlib, JPEG, etc.) and NULL compressor for uncompressed tiles.

  - The refs data.frame works directly with arrow::write_parquet() for
    large reference sets spanning thousands of files.

Rust stack

Built on async-tiff 0.2 (Development Seed) and object_store 0.13 (Apache
arrow-rs) via extendr 0.7. Async I/O is handled by tokio, with a runtime
created per call. All cloud credential resolution follows object_store
conventions (environment variables, instance profiles, anonymous access
via anon = TRUE).

Supported formats

Tiled TIFF and COG files. Strip-based IFDs are skipped (no tile
offsets). All standard COG compression methods are supported: deflate,
JPEG, LZW, zstd, uncompressed. Data types: uint8, uint16, uint32,
uint64, int8, int16, int32, int64, float32, float64.

GeoTIFF metadata

EPSG codes are extracted from GeoTIFF key directory, trying
ProjectedCSType first and falling back to GeographicType. Files without
GeoTIFF keys return NA for crs_epsg.

Performance

Metadata scanning is network-bound (2–3 HTTP range requests per COG). A
19,000-tile file scans in ~0.4 seconds. Single tile decode runs at ~0.5
seconds including connection setup; batched tiles amortize the setup
cost to ~20ms per additional tile. Comparable to or faster than GDAL
/vsicurl/ for equivalent operations.

Known limitations

  - File scanning is sequential across multiple paths. Concurrent
    scanning via tokio join_all is the obvious next step.
  - Kerchunk JSON output is V1 format. Kerchunk parquet (the
    VirtualiZarr format consumed by xarray) is a planned addition.
  - GDAL's Zarr driver cannot yet reliably read the Kerchunk JSON
    output; this depends on GDAL Kerchunk driver maturation.
  - No CRS transformation or spatial subsetting — the package returns
    tile indices, not geographic queries. Use grout for tile/extent
    mapping.