GRIB2 - DATA REPRESENTATION TEMPLATE 5.42

Grid point and spectral data - CCSDS szip

Created 01/18/2012


Octet No. Contents
12-15
Reference value (R) (IEEE 32-bit floating-point value)
16-17
Binary scale factor (E)
18-19
Decimal scale factor (D)
20
Number of bits required to hold the resulting scaled and referenced data values.
21
Type of original field values (see Code Table 5.1)
22 szip options mask
23 szip bits per pixel
24-25 szip pixel per block
26-27 szip pixel per scan line


Notes:

(1) The intent of this template is to scale the grid point data to obtain desired precision, if appropriate, and then subtract out reference value from the scaled field as is done using Data Representation Template 5.0. After this, the resulting grid point field can be treated as a grayscale image and is then encoded into the CCSDS szip code stream format. To unpack the data field, the CCSDS szip code stream is decoded back into an image, and the original field is obtained from the image data as described in regulation 92.9.4, Note (4).

(2) The Consultative Committee for Space Data Systems (CCSDS) szip is the standard used by space agencies for then compression of scientific data transmitted from satellites and other space instruments. CCSDS szip is a very fast predictive compression algorithm based on the extended-Rice algorithm, irs uses Golomb-Rice codes for entropy coding. The sequence of prediction errors is divided into blocks. Each block is compressed using a two-pass algorithm. In the first pass the best coding method for whole block is determined. In the second pass, output of the marker of the selected coding method as a side information is done along with prediction errors endcoded. The coding methods include:
   - Golomb-Rice codes of chosen rank
   - Unary code for transformed pairs of prediction errors
   - Fixed-length natural binary code if the block is found to be incompression
   - Signaling to the decoder empty block if all prediction errors are zeroes
A detailed description can be found in:
   Consulative Committee for Space Data Systems: Lossless data Compression.
Blue Book, May 1997.
      CCSDS szip is often confused with a general-purpose compression utiltity by Schindler, which is also called szip.

(3) Negative values of E or D shall be represented according to Regulation 92.1.5.


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