HGrib

Unofficial bindings for ECMWF's GRIB API library for reading WMO FM-92 GRIB edition 1 and edition 2 messages.

In this version of HGrib, raw bindings for the documented part of GRIB API is available. Future versions are intended to include a higher-level Haskell interface.

Installation

The following prerequisites are needed to build HGrib:

• GRIB API >= 1.12 installed and discoverable by ghc (use cabal's --extra-include-dirs and --extra-lib-dirs if it's installed at a custom location); and

• Haskell base >= 4.5; and

• c2hs == 0.26.*.

With these requirements available, HGrib can be installed from Hackage with Cabal:

cabal install hgrib

Usage

Right now, only raw bindings for the documented part of GRIB API is available in Data.Grib.Raw. Much of the documentation is copied into HGrib's reference documentation generated by Haddock. To be able to work with these bindings, bindings for C's fopen is provided in Data.Grib.Raw.CFile (which is re-exported by Data.Grib.Raw). An example of usage is GRIB API's get.c example re-written with HGrib's bindings:

import Control.Exception (assert)
import Data.Grib.Raw
import Foreign           (allocaArray, allocaBytes)
import Text.Printf       (printf)


filename :: FilePath
filename = "test/stage/regular_latlon_surface.grib1"

assertIO :: Bool -> IO ()
assertIO = flip assert $ return ()

main :: IO ()
main = do
  h <- withBinaryCFile filename ReadMode $
         gribHandleNewFromFile defaultGribContext

  _ <- gribSetString h "file" filename

  gribGetLong h "Ni" >>= printf "numberOfPointsAlongAParallel=%d\n"
  gribGetLong h "Nj" >>= printf "numberOfPointsAlongAMeridian=%d\n"

  gribGetDouble h "yFirst" >>= printf "latitudeOfFirstGridPointInDegrees=%g\n"
  gribGetDouble h "xFirst" >>= printf "longitudeOfFirstGridPointInDegrees=%g\n"
  gribGetDouble h "yLast"  >>= printf "latitudeOfLastGridPointInDegrees=%g\n"
  gribGetDouble h "xLast"  >>= printf "longitudeOfLastGridPointInDegrees=%g\n"
  gribGetDouble h "DyInDegrees" >>= printf "jDirectionIncrementInDegrees=%g\n"
  gribGetDouble h "DxInDegrees" >>= printf "iDirectionIncrementInDegrees=%g\n"

  len <- gribGetLength h "packingType"
  allocaBytes len $ \bufr -> do
    packingType <- gribGetString h "packingType" bufr len
    printf "packingType=%s (%d)\n" packingType (length packingType + 1)

  size <- gribGetSize h "values"
  allocaArray size $ \array -> do
    values <- gribGetDoubleArray h "values" array size
    let average = sum values / (fromIntegral . length $ values)
    printf "There are %d values, average is %g\n" size average

  len' <- gribGetLength h "file"
  assertIO $ len' == 1 + length filename
  allocaBytes len' $ \bufr' -> do
    file <- gribGetString h "file" bufr' len'
    assertIO $ file == filename

Contributing

Issues and pull requests are most welcome! In particular, let me know if there is any undocumented part of GRIB API that you would like to have included.

Licenses

HGrib was created and is currently maintained by Mattias Jakobsson. It is released under the GNU General Public License v3.0. ECMWF's GRIB API is released under the Apache license. HGrib is in no way associated with ECMWF or the original library.