Supported formats

Raster formats

Format	Read	Write	Feature flag	Notes
GeoTIFF	✓	✓	(always)	Predictor 1/2/3, DEFLATE, LZW, GDAL_NODATA
Cloud Optimized GeoTIFF (COG)	✓	—	`cloud`	HTTP range reads; write not supported yet
Zarr (via `zarrs`)	✓	—	`zarr`	Azure Blob + Planetary Computer auth
NetCDF	✓	—	`netcdf`	Requires libnetcdf system library
GRIB2	✓	—	`grib`	Requires libgribapi or eccodes
JP2000, HDF4, ECW, MrSID, ERDAS .img	—	—	—	Use GDAL

Vector formats

Format	Read	Notes
GeoJSON (`.geojson`, `.json`)	✓
Shapefile (`.shp` + sidecar files)	✓	Via `shapefile` crate
GeoPackage (`.gpkg`)	✓	Via `rusqlite`

Vector writing is not supported in v0.7.0. Clip / rasterize accept vectors as input; produce rasters as output.

For float element types (f32, f64), the GDAL_NODATA tag value is replaced with NaN on read. Algorithms treat NaN as “invalid” and propagate it as such — no sentinel values buried inside floats.

On write, the same convention: NaN pixels are written out as GDAL_NODATA values if the output format supports the tag.

For integer types (i16, u16, u8), the original nodata sentinel is preserved.

Endianness and TIFF predictors

The native GeoTIFF reader handles both big-endian and little-endian files. Predictor 1 (no prediction), 2 (horizontal differencing), and 3 (floating-point prediction) are all supported. Predictor 3 was added in v0.6.21 specifically for Copernicus DEM GLO-30 which uses it.

Compression support

Read: DEFLATE, LZW, packbits, none. Write: DEFLATE (via --compress flag) or none.

Write support for LZW is not planned — DEFLATE compresses better on geospatial rasters for comparable CPU cost.

Size limits

The tiff crate enforces a default size limit to prevent malicious inputs. For large DEMs (e.g. 20,000 × 20,000 or bigger), SurtGIS sets Limits::unlimited() internally so uncompressed reads aren’t rejected.

Files on disk can be arbitrarily large; streaming algorithms don’t care about total size.

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