In GRIB edition 2 what are these Product Definition Templates?
The purpose of the Product Definition section is to describe the nature of the data contained in the Data section.
The Product Definition section has a number to signify the different templates. This is called the Product Definition Template Number or PDTN for short. The ecCodes key for this is productDefinitionTemplateNumber.
Note that there are three categories of GRIB2 templates – Grid Definition Templates, Product Definition Templates, and Data Representation Templates. They are identified by the Grid Definition Template Number, Product Definition Template Number, and Data Representation Template Number, respectively.
The Product Definition Templates are normally divided into groups of 4. For example the most commonly used ones are:
| Deterministic | Ensemble | |
|---|---|---|
| Instantaneous | 0 | 1 |
| Interval-based | 8 | 11 |
So we have two dimensions:
- Whether it is deterministic or an ensemble
- Whether the field is instantaneous or interval-based (e.g. accumulated)
So a Product Definition Template Number of 8 means "deterministic and interval-based". If you chose 11 then your product represents an ensemble member for which you get the key "perturbationNumber".
For meaning of codes, see http://apps.ecmwf.int/codes/grib/format/grib2/templates/4/