| 1 | User Tables Wesley Ebisuzaki |
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| 2 | ---- ------ |
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| 3 | |
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| 4 | GRIB files describe the contents (example, zonal wind, temperature) by |
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| 5 | a parameter table and parameter number. Since the size of the parameter |
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| 6 | table is limited to 255 entries, groups are finding (1) that they want |
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| 7 | to use their own parameter table and (2) large groups are finding that |
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| 8 | they have to use multiple parameter tables. |
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| 9 | |
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| 10 | The parameter table used by wgrib is determined by (v1.5.0 and later) |
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| 11 | |
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| 12 | use built-in tables |
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| 13 | use user-defined table if available |
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| 14 | use built-in NCEP-2 table (warning under certain conditions) |
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| 15 | |
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| 16 | Alternatively, if wgrib is compiled with the "-D P_TABLE_FIRST" |
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| 17 | option, then the search order is, |
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| 18 | |
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| 19 | use user-defined table if available |
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| 20 | use built-in tables |
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| 21 | use built-in NCEP-2 table (warning under certain conditions) |
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| 22 | |
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| 23 | [This is the preferred search order for foreign-language parameter tables.] |
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| 24 | |
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| 25 | |
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| 26 | The name of the user-defined table is searched for in |
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| 27 | |
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| 28 | 1) the environment variable "GRIBTAB" |
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| 29 | 2) the environment variable "gribtab" |
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| 30 | 3) the file gribtab |
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| 31 | |
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| 32 | Defining an environment variable depends on the operating system |
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| 33 | and on the shell. |
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| 34 | |
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| 35 | example |
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| 36 | export GRIBTAB=~/data/gribtab (bash) |
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| 37 | setenv GRIBTAB ~/data/gribtab (csh) |
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| 38 | GRIBTAB=$HOME/data/gribtab ; export GRIBTAB (sh) |
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| 39 | |
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| 40 | |
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| 41 | |
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| 42 | The format of the GRIBTAB file is |
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| 43 | |
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| 44 | ----------------------------------------------------------------------- |
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| 45 | -1:CENTER:SUBCENTER:PARAMETER_TABLE |
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| 46 | 0:name:comment |
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| 47 | 1:name:comment |
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| 48 | ... |
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| 49 | 255:name:comment |
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| 50 | |
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| 51 | -1:CENTER:SUBCENTER:PARAMETER_TABLE |
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| 52 | 0:name:comment |
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| 53 | 1:name:comment |
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| 54 | ... |
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| 55 | 255:name:comment |
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| 56 | |
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| 57 | (etc.) |
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| 58 | ----------------------------------------------------------------------- |
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| 59 | |
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| 60 | "CENTER" is number between 0 and 255 with -1 being a wildcard. |
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| 61 | "SUBCENTER" is number between 0 and 255 with -1 being a wildcard. |
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| 62 | "PARAMETER_TABLE" is number between 0 and 255 with -1 being a wildcard. |
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| 63 | "name" is a string with the variable name "TMP". |
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| 64 | "comment" is a string such describing the variable such as "temperature [K]" |
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| 65 | Any missing parameter lines will be given a generic name and comment. |
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| 66 | |
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| 67 | Each GRIB record contains the center (PDS octet 5), subcenter (PDS octet 26) |
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| 68 | and parameter_table (PDS octet 4). The names and comments from the |
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| 69 | first section to match the center-subcenter-parameter_name in the PDS |
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| 70 | are used. Currently the subcenter are not used in matching the |
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| 71 | built-in tables. This will probably change when sub-centers start using |
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| 72 | their own parameter tables. |
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| 73 | |
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| 74 | Policy |
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| 75 | |
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| 76 | The wgrib code is easily modified to add new built-in parameter tables. |
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| 77 | New tables will be added under the following conditions: a reasonable |
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| 78 | number of users, I don't have to type it in and the table is reasonably |
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| 79 | stable. (Rules subject to change.) |
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| 80 | |
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