module-netcdf.md

module: (curry netcdf)

NetCDF classic format reader — the self-contained, documented binary format used for gridded scientific data (climate, oceanography, and similar time/space datasets).

Prerequisites

Pure Scheme — no C module, no build step, no external library. Works everywhere curry runs.

Scope

Supports NetCDF classic (CDF-1) and 64-bit-offset (CDF-2) files — read only, no writer. Does not support NetCDF-4 (which is HDF5-backed — use (curry hdf5) for those files instead) or CDF-5 (64-bit data, a distinct on-disk layout). Both fixed-size and record (unlimited-dimension) variables are supported, including files with multiple interleaved record variables.

API

(import (curry netcdf))

(netcdf-open path)                  ; -> handle
(netcdf-variable nc name)           ; -> (values tensor dim-names)
(netcdf-attributes nc [var-name])   ; -> alist; global attrs if var-name omitted
(netcdf-dimensions nc)              ; -> alist of (name . length); #f length = unlimited
(netcdf-close nc)

netcdf-open parses the header only — variable data is read lazily, one netcdf-variable call at a time, so opening a file with large variables doesn't load them into memory until asked for.

For a record variable, netcdf-variable returns a tensor whose first dimension is the current record count (numrecs), with the remaining dimensions from the variable's declared shape.

Example

(import (curry netcdf))

(define nc (netcdf-open "data.nc"))
(display (netcdf-dimensions nc)) (newline)

(call-with-values
  (lambda () (netcdf-variable nc "temperature"))
  (lambda (temp dim-names)
    (display (tensor-shape temp)) (newline)
    (display (tensor-ref temp 0 0)) (newline)))

(display (netcdf-attributes nc "temperature")) (newline)
(netcdf-close nc)

See also

• docs/reference/module-fits.md — FITS image reader/writer
• docs/reference/module-hdf5.md — HDF5 FFI wrapper (for NetCDF-4 files)