Commission for basic systems meeting of expert team on data representation and codes




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WORLD METEOROLOGICAL ORGANIZATION

COMMISSION FOR BASIC SYSTEMS
MEETING OF EXPERT TEAM ON DATA

REPRESENTATION AND CODES
KUALA LUMPUR, MALAYSIA, 21 - 26 JUNE 2004



ET DR&C/Doc. 3.8(1)

ITEM: 3.8
(11.VI.2004)

ENGLISH ONLY




IMPLICATIONS AND NEED FOR A NEW EDITION OF CREX


(Submitted by the Secretariat)
________________________________________________________________
Summary and Purpose of Document
This document discusses the implications of a New edition for BUFR and for CREX. Some possible additions are proposed for a new edition of CREX.

________________________________________________________________


Action Proposed
The meeting is invited consider the issue of new edition and approved the few additions proposed for CREX, and draw the appropriate modification, conclusion and/or recommendation.
APPENDIX:

Differences in representing the data/products in BUFR and CREX



Reference:

[1] Manual on Codes, WMO - No 306, Volumes I.2.



DISCUSSION
1. In Appendix an excellent table originally made by Atsushi Shimazaki is listed. It shows the existing difference between BUFR and CREX. To ease the conversion between BUFR and CREX it might be appropriate to add features to CREX to make a new edition. Following the problems encountered during the Y2K crisis, it was proposed to modify the system of reporting dates in BUFR, using the opportunity of creating a new edition.


  1. Implications of a new edition of BUFR and CREX

The implementation of a new edition of BUFR and CREX at a time of the migration to TDCF will not be so simple for the countries that are struggling to switch to TDCF. All the decoding software will have to be changed to accept new edition data. Encoding systems will have to be progressively adjusted to produce data in the new edition format. It will be a migration within the migration and one has to be aware that the migration to TDCF process will be substantially more complicated. If advanced centres have not too much difficulty for changing their software, it will be more difficult to be understood and implemented by developing countries. When one tries to sell the migration because it will simplify code changes, it will be difficult to explain that one has to change everything again. The point of view of the secretariat would be to delay the new edition up to 2010, when the migration process of basic data should be completed. Members of the team will have to discuss this opinion and make appropriate recommendations.




  1. If a new edition is made for BUFR, it is also proposed to make a new edition for CREX. The new edition for CREX could include features, which will be useful and may be requested also in processing CREX messages. The following features are proposed for addition in CREX:



Version number of local table

Typical date/time

Originating centre

Originating sub-centre international

Update sequence No.

Data category

Data sub-category international

Section 1 - Data description section
Group No. Contents Meanings
1 Ttteevvww T : Indicator for CREX Tables

tt : CREX Master table used (00 for WMO standard FM 95 CREX tables)

ee : CREX edition number (currently 01)

vv : CREX table version number (currently 01)

ww : Version number of local table


  1. Yyyyymmdd yyyy: Typical year

mm: Typical month

dd: Typical day



  1. Hhhnn hh: Typical hour

nn: Typical minute

4 Annnmmm A : Indicator for CREX Table A entry

nnn : Data category from CREX Table A

mmm : International data sub-category from Common table C-13

5 Poooooppp ooooo Originating Centre from Common table C-11

ppp Originating sub-centre from Common table C-12

6 Uuu uu Update sequence number (00 for original message, uu for updated version)

7 to n Bxxyyy, B, C, D: Indicators for CREX Tables B,C,D entries

Cxxyyy, xxyyy: 5 digits each which indicates references from CREX Tables

Dxxyyy, B, C and/or D

and/or Rxxyyy: R: Indicator for replication:

xx: number of replicated descriptors



yyy: number of replications (delayed replication if yyy= 0)
APPENDIX:
Differences in representing the data/products in BUFR and CREX


Items for definition

BUFR new ed.

existing CREX

CREX new ed.

Remarks

OCTETS OF SECTIONS

Beginning with code name

yes

yes

yes




Length of section

yes

no

no

Same function for delimiting sections

Section terminator

no

yes

yes

Master table used

yes

yes

yes




Edition number

yes

yes

yes




Version number of master table

yes

yes

yes




Version number of local table

yes

no

yes




Originating centre

yes

no

yes




Originating sub-centre international

yes

no

yes




Originating sub-centre local

yes

no

no




Update sequence No.

yes

no

yes




Data category

yes

yes

yes




Data sub-category international

yes

no

yes




Data sub-category local

yes

no

no




Typical date/time

yes

no

yes




Total length of message

yes

no

no

Same function for delimiting message

Number of data subset

yes

no

no

Subset terminator

no

yes

yes

Data compression

yes

no

no




Check digit

no

yes

yes




Space characters as separator

no

yes

yes




End with 7777

yes

yes

yes



















DESCRIPTORS

Table B

yes

yes

yes

F=B in CREX,

Non-SI Units used in CREX,

No data description operator qualifier

(class 31) in CREX


Table C

yes

yes

yes

F=C in CREX,

Limited number of descriptors, but additional unit replacement descriptor in CREX



Table D

yes

yes

yes

F=D in CREX,

No satellite, image and radar data related categories in CREX



(Delayed) replication

yes

yes

yes

F=R in CREX,

Without a replication factor (descriptor) in CREX



Code table

yes

yes

yes




Flag table

yes

yes

yes

Octal representation in CREX

Additional field

yes

no

no





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