s2-tools/dist/readers/grib2/sections/7/complexUnpacking.d.ts

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import type { Grib2Sections } from '..';
import type { Reader } from '../../..';
/**
 * # Data Template 7.2 - Grid Point Data - Complex Packing
 *
 * ## Contents
 * - **6-xx**: NG group reference values (X1 in the decoding formula), each of which is encoded using
 * the number of bits specified in octet 20 of data representation template 5.0. Bits set to zero shall
 * be appended as necessary to ensure this sequence of numbers ends on an octet boundary
 * - **[xx+1]-yy**: NG group widths, each of which is encoded using the number of bits specified in
 * octet 37 of data representation template 5.2. Bits set to zero shall be appended as necessary to
 * ensure this sequence of numbers ends on an octet boundary
 * - **[yy+1]-zz**: NG scaled group lengths, each of which is encoded using the number of bits
 * specified in octet 47 of data representation template 5.2. Bits set to zero shall be appended as
 * necessary to ensure this sequence of numbers ends on an octet boundary (see Note 5)
 * - **[zz+1]-nn**: Packed vaules (X2 in the decoding formula), where each value is a deviation from
 * its respective group reference value
 *
 * ## Notes
 * - (1) Group descriptors mentioned above may not be physically present; if associated field width is 0.
 * - (2) Group lengths have no meaning for row by row packing; for consistency, associated field width
 *  should then be encoded as 0. So no specific test for row case is mandatory at decoding software level
 *  to handle endcoding/decoding of group descriptors.
 * - (3) Scaled group lengths, if present, are encoded for each group. But the true last group length
 *  (unscaled) should be taken from data representation template.
 * - (4) For groups with a constant value, associated field width is 0, and no incremental data are
 *  physically present.
 * - (5) The essence of the complex packing method is to subdivide a field of values into NG groups,
 * where the values in each group have similar sizes. In this procedure, it is necessary to retain
 * enough information to recover the group lengths upon decoding. The NG group lengths for any given
 * field can be described by Ln = ref + Kn x len_inc, n = 1, NG, where ref is given by octets 38 - 41
 * and len_inc by octet 42. The NG values of K (the scaled group lengths) are stored in the data section,
 * each with the number of bits specified by octet 47. Since the last group is a special case which
 * may not be able to be specified by this relationship, the length of the last group is stored in
 * octets 43-46.
 *
 * # Data Template 7.3 - Grid Point Data - Complex Packing and Spatial Differencing
 *
 * ## Contents
 * - **6-ww**: First value(s) of original (undifferenced) scale values, followed by the overall
 * minimum of the differences. The number of values stored is 1 greater than the oerder of
 * differentiation, and the field width is described at octet 49 of data representation template
 * 5.3 (see Note 1)
 * - **[ww+1]-xx**: NG group difference values, (X1 in the decoding formula), each of which is
 * encoded using the number of bits specified in octet 20 of data representation template 5.0. Bits
 * set to zero shall be appended where necessary to ensure this sequence of numbers ends on an octet
 * boundary
 * - **[xx+1]-nn**: Packed vaules (X2 in the decoding formula), where each value is a deviation from
 * its respective group reference value
 *
 * ## Notes
 * - (1) Referring to the notation in Note 1 of data representation template 5.3, at order 1, the
 * values stored in octet 6-ww are g1 and gmin. At order 2, the values stored are h1, h2 and hmin.
 * - (2) Extra descriptors related to spatial differencing are added before the splitting descriptors,
 * to refect the separation between the two approaches. It enables to share software parts between cases
 * with and without spatial differencing.
 * - (3) The position of overall minimum after initial data values is a choice that enables less
 * software management.
 * - (4) Overall minimum will be negative in most cases. First bit should indicate the sign:0 if
 * positive, 1 if negative.
 * @param reader - Binary data reader positioned at the start of the data section.
 * @param sections - A collection of all sections in the GRIB file.
 * @returns An array of decoded values.
 */
export declare function complexUnpacking(reader: Reader, sections: Grib2Sections): number[];
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