Grid Point Data - Complex Packingi and Spatial Differencing

Created 01/19/2012

Note:  For most templates, details of the packing process are described in Regulation 92.9.4.

Octet No. 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


(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.