Struct Grib2SubmessageDecoder 

pub struct Grib2SubmessageDecoder { /* private fields */ }

Decoder for grid point values of GRIB2 submessages.

Examples

use grib::Grib2SubmessageDecoder;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let f = std::fs::File::open(
        "testdata/Z__C_RJTD_20160822020000_NOWC_GPV_Ggis10km_Pphw10_FH0000-0100_grib2.bin",
    )?;
    let f = std::io::BufReader::new(f);
    let grib2 = grib::from_reader(f)?;
    let (_index, first_submessage) = grib2.iter().next().unwrap();

    let decoder = Grib2SubmessageDecoder::from(first_submessage)?;
    let mut decoded = decoder.dispatch()?;
    assert_eq!(decoded.size_hint(), (86016, Some(86016)));

    let first_value = decoded.next();
    assert_eq!(first_value.map(|f| f.is_nan()), Some(true));

    let non_nan_value = decoded.find(|f| !f.is_nan());
    assert_eq!(non_nan_value.map(|f| f.round()), Some(1.0_f32));

    let last_value = decoded.last();
    assert_eq!(last_value.map(|f| f.is_nan()), Some(true));
    Ok(())
}

If the byte sequences for Sections 5, 6, and 7 of the GRIB2 data are known, and the number of grid points (described in Section 3) is also known, it is also possible to create a decoder instance by passing them to Grib2SubmessageDecoder::new. The example above is equivalent to the following:

use std::io::Read;

use grib::Grib2SubmessageDecoder;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let f = std::fs::File::open(
        "testdata/Z__C_RJTD_20160822020000_NOWC_GPV_Ggis10km_Pphw10_FH0000-0100_grib2.bin",
    )?;
    let mut f = std::io::BufReader::new(f);
    let mut buf = Vec::new();
    f.read_to_end(&mut buf)?;

    let decoder = Grib2SubmessageDecoder::new(
        86016,
        buf[0x0000008f..0x000000a6].to_vec(),
        buf[0x000000a6..0x000000ac].to_vec(),
        buf[0x000000ac..0x0000061b].to_vec(),
    )?;
    let mut decoded = decoder.dispatch()?;
    assert_eq!(decoded.size_hint(), (86016, Some(86016)));

    let first_value = decoded.next();
    assert_eq!(first_value.map(|f| f.is_nan()), Some(true));

    let non_nan_value = decoded.find(|f| !f.is_nan());
    assert_eq!(non_nan_value.map(|f| f.round()), Some(1.0_f32));

    let last_value = decoded.last();
    assert_eq!(last_value.map(|f| f.is_nan()), Some(true));
    Ok(())
}

Implementations

impl Grib2SubmessageDecoder

pub fn new( num_points_total: usize, sect5_bytes: Vec<u8>, sect6_bytes: Vec<u8>, sect7_bytes: Vec<u8>, ) -> Result<Self, GribError>

Creates an instance from the number of grid points (described in Section 3) and byte sequences for Sections 5, 6, and 7 of the GRIB2 data.

For code examples, refer to the description of this struct.

pub fn from<R: Grib2Read>( submessage: SubMessage<'_, R>, ) -> Result<Self, GribError>

Sets up a decoder for grid point values of submessage.

pub fn dispatch( &self, ) -> Result<Grib2DecodedValues<'_, impl Iterator<Item = f32> + '_>, GribError>

Dispatches a decoding process and gets an iterator of decoded values.

pub fn section5(&self) -> &Section5

Provides access to the parameters in Section 5.

Examples

use grib::Grib2SubmessageDecoder;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let f = std::fs::File::open(
        "testdata/Z__C_RJTD_20160822020000_NOWC_GPV_Ggis10km_Pphw10_FH0000-0100_grib2.bin",
    )?;
    let f = std::io::BufReader::new(f);
    let grib2 = grib::from_reader(f)?;
    let (_index, first_submessage) = grib2.iter().next().unwrap();

    let decoder = Grib2SubmessageDecoder::from(first_submessage)?;
    let actual = decoder.section5();
    let expected = grib::def::grib2::Section5 {
        header: grib::def::grib2::SectionHeader {
            len: 23,
            sect_num: 5,
        },
        payload: grib::def::grib2::Section5Payload {
            num_encoded_points: 86016,
            template_num: 200,
            template: grib::def::grib2::DataRepresentationTemplate::_5_200(
                grib::def::grib2::template::Template5_200 {
                    num_bits: 8,
                    max_val: 3,
                    max_level: 3,
                    dec: 0,
                    level_vals: vec![1, 2, 3],
                },
            ),
        },
    };
    assert_eq!(actual, &expected);

    Ok(())
}