Section 5 - Template 61 : Grid point data - simple packing with logarithm pre-processing
Templates for Section 5
More Sections
| Octets | Key | Type | Content |
| 12-15 | referenceValue | real | Reference value (R) (IEEE 32-bit floating-point value) |
| 16-17 | binaryScaleFactor | signed | Binary scale factor (E) |
| 18-19 | decimalScaleFactor | signed | Decimal scale factor (D) |
| 20 | bitsPerValue | unsigned | Number of bits used for each packed value |
| 21-24 | preProcessingParameter | real | Pre-processing parameter (B) (IEEE 32- bit floating-point value) |
( 0) Preliminary Note: This template is experimental, was not validated at the time of publication and should be used only for bi-lateral previously agreed tests.
( 1) This template is appropriately designed for data sets with all non-negative values and a wide variability range (more then 5 orders of magnitude). It must not be used for data sets with negative values or smaller variability range.
( 2) A logarithm pre-processing algorithm is used to fit the variability range into one or two order of magnitudes before using the simple packing algorithm. It requires a parameter (B) to assure that all values passed to the logarithm function are positive. Thus scaled values are Z=ln(Y+B), where Y are the original values, ln is the natural logarithm function and B is chosen so that Y+B>0.
( 3) Best practice follows for choosing the B pre-processing parameter.
1 If the data set minimum value is positive, B can be safely put to zero.
2 If the data set minimum is zero, all values must be scaled to become greater than zero and B can be equal to the minimum positive value in the data set.
( 4) Data shall be packed using Data template 7.