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TDLPACK.md

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TDLPACK

TDLPACK File Types

Before we describe the TDLPACK data format, one first needs to know the different types of files in which a TDLPACK record can be reside in. There a two file types: Fortran unformatted (variable record length); Fortran direct-access (fixed record length). In MOS2K world, these are known as sequential and random access files, respectively.

Sequential Files

This is a Fortran unformatted, variable record length file. The TDLPACK record is contained within a Fortran record. The TDLPACK record preceeded by 8-bytes that contains the record length in bytes of the TDLPACK record. A TDLPACK sequental file can also contain 2 other type of records: station call letter record; trailer record. Station call letters in MOS2K of of type CHARACTER*8.

Station call letter record is of the following format in bytes:

  • 1 - 8: Size of the station call letters in bytes (number of stations * 8)
  • 9 - n: Station Call Letters

Trailer record is of the following format in bytes:

  • 1 - 8: Record length
  • 9 - n: Trailer record consisting of date/time information

Random Access Files

This is a Fortran direct access, fixed record length file. One can think of these files like a book in that there is a table of contents (i.e. key records) that point to where specific TDLPACK records (i.e. data records) exist within the file. Also, there exists a Master Key Record at the beginning of the file. In a Random Access File, a TDLPACK record is considered a logical record because it can span multiple (Fortran) physical records. A TDLPACK random access file can also contain a station call letter record and is the same format as discussed above, however, accessing this record is different.

TDLPACK Data Format

The following will attempt to briefly explain the TDLPACK format. Please read the official documentation here. TDLPACK is a big-endian binary data format and is GRIB-like in that it contains an initial 4-character string to identify the data format "TDLP"; indentification sections (Indicator, Product, and Grid); Data section; and an End Section that contains "7777". A more detailed description of TDLPACK sections can be found in the chapter 5 of the official documentation. TDLPACK contains the following sections:

  • Section 0 - Indictator Section
  • Section 1 - Product Definition Section
  • Section 2 - Grid Definition Section (NOTE: Not present when data are vector)
  • Section 3 - Bitmap Section (defined, but never supported in code)
  • Section 4 - Data Section
  • Section 5 - End Section

A TDLPACK record can contain 2 types of data: vector data (i.e. most likely data at "stations"); gridded data (i.e. data at regularly spaced projected gridpoints). TDLPACK only supports the following map projections:

  • Lambert Conformal Conic
  • Polar Stereograhic
  • Mercator

There is no support for geographic grids (i.e. latitude-longitude grids).