GRIB API学习笔记06——grib_filter
1.1. 介绍
高级命令行工具
迭代输入的所有消息，对每个消息应用一组用户定义的规则。
规则由GRIB API提供的微型语言构成，这种微语言不具有完整编程语言的能力。
通过key访问消息中的数据
打印消息的内容
设置消息中的数据值
使用控制结构
将消息写入硬盘
1.2. 用法
[shell]grib_filter rules_file [-o out_file] _in_file1 in_file2…[/shell]
每个输入文件都按照rules_file中的规则进行处理。
只有在使用write语句时才将grib消息写入输出文件。
rules_file中的每个语句以分号“;”结尾。
rules_file中的语法错误按行号报错。例
$ grib_filter rules.filter uv500.grib2 | more GRIB_API ERROR : grib_parser: syntax error at line 2 of rules.filter rules.filter: error unable to create action
1.3. 规则语法
1.3.1. print
print “输出的文本”; # 注释
print “some text [key]”;
打印到标准输出
输出方括号中的key的值
如果没有在消息中找到[key]的值，则显示”undef”
[key] -> 原始类型
[key:l] -> integer (the “el” is for “long”!)
[key:s] -> string
[key:d] -> double
[key!c%F’S’] -> arrays: c->columns F->format (C style) S->separator ****
print (“filename”) “some text [key]”;
例1：
以下例子中，我使用uv500.grib2作为示例grib文件。文件内容如下
>grib_ls uv500.grib2 uv500.grib2 edition centre date dataType gridType stepRange typeOfLevel level shortName packingType 2 babj 20131031 fc regular_ll 1 isobaricInhPa 500 u grid_jpeg 2 babj 20131031 fc regular_ll 1 isobaricInhPa 500 v grid_jpeg 2 of 2 grib messages in uv500.grib2 2 of 2 total grib messages in 1 files
# A simple print print “ed = [edition], centre is [centre:s] = [centre:l]”;
命令：
>grib_filter rules.filter uv500.grib2 ed=2,centre is babj=38 ed=2,centre is babj=38
例2
# one column 3 decimal digits print “[distinctLatitudes!1%.3f]”;
命令：
$ grib_filter rules.filter uv500.grib2 | more 64.350 64.200 64.050 63.900
例3：
# three columns 5 decimal digits comma separated print “[latLonValues!3%.5f’,’]”; $ grib_filter rules.filter uv500.grib2 | more 64.35000,70.00000,11.97201, 64.35000,70.15000,11.96721, 64.35000,70.30000,11.95121, 64.35000,70.45000,11.92721, ...
1.3.2. write
write;
将当前消息写入命令行中-o参数指定的输出文件( grib_filter –o outfile rules_file grib_file).
如果-o参数没设置，则默认输出到“filter.out” 文件。
write “filename__[key]”;
将当前消息写入到文件“filename[key]”中，其中方括号中的key用消息中该key的值代替。
需要注意的副作用：如果两个消息的键值不一样，将被写入不同的文件。
例4：
# Creating multiple files write “[centre]_[dataDate]_[step].grib[edition]”; $ grib_filter rules.filter uv500.grib2 $ ls babj_20131031_1.grib2 data rules.filter uv500.grib2
1.3.3. append
append;
将当前消息附加到输出文件（由-o定义），默认文件为filter.out。
append “filename_[key]”;
将当前消息附加到输出文件“filename[key]_”，其中[key]由相应key的值替换.
如果文件不存在，则创建。
如果两个消息key的值不一样，将附加到不同的文件中。
例5：
append;
命令：
$ grib_count uv500.grib2 2 $ grib_filter rules.filter -o out.grib2 uv500.grib2 $ grib_count out.grib2 2
1.3.4. set
**set key1 = key2; ** # 将key1设置为key2的值 ****
**set key = {val1,val2,val3,val4}; ** # 设置数组 ****
**set key = “string”; ** # 设置字符串 ****
set key = expression ; ** # 设置key为表达式的值
set key = MISSING ; ** # 设置为****missing
表达式运算符:
== equal to
is equal to for strings
!= not equal to
|| or
&& and
! Not
Arithmetic operators * / + –
()
例6：
set edition = 2; write “[file][edition]”; $ grib_filter rules.filter uv500.grib2 $ ls babj_20131031_1.grib2 data out.grib2 rules.filter uv500.grib2 uv500.grib21
例7：
set values = {12.2,14.8,13.7,72.3};
print “values = { [values] }”;
write “[file][edition]”;
$ grib_filter rules.filter uv500.grib2
values = { 12.2 14.7996 13.7 72.2996 }
values = { 12.2 14.7996 13.7 72.2996 }
$ ls
data rules.filter uv500.grib2 uv500.grib22
$ $ grib_dump uv500.grib22
***** FILE: uv500.grib22
#============== MESSAGE 1 ( length=304 ) ==============
GRIB {
…
values(4) = {
1.2199999809e+01, 1.4799609184e+01, 1.3699999809e+01, 7.2299609184e+01
}
#-READ ONLY- maximum = 72.2996;
#-READ ONLY- minimum = 12.2;
#-READ ONLY- average = 28.2498;
#-READ ONLY- numberOfMissing = 0;
#-READ ONLY- standardDeviation = 25.4489;
#-READ ONLY- skewness = -75825.8;
#-READ ONLY- kurtosis = 3.90899e+06;
#-READ ONLY- isConstant = 0;
#-READ ONLY- getNumberOfValues = 4;
}
…
1.3.5. transient
transient key1 = key2;
定义一个新的key1，并将key2的值赋给它
transient key1 = “string”;
transient key1 = expression ;
expression operators :
== equal to
is equal to for strings
!= not equal to
|| or
&& and
! not
Arithmetic operators * / + –
()
例8：
transient mystep = step + 24; print “step = [step] mystep = [mystep]”; $ grib_filter rules.filter uv500.grib2 step = 1 mystep = 25 step = 1 mystep = 25
1.3.6. if语句
if ( expression ) { instructions }
if ( expression ) { instructions } else { instructions } ****
expression operators :
n == equal to
n is equal to for strings
n != not equal to
n || or
n && and
n ! not
n Arithmetic operators * / + –
n ()
例9：该例子没有实际实验
if (localDefinitionNumber == 1) {
set edition = 2;
write;
}
> grib_filter –o out.grib2 rule.filter x.grib1
> ls
out.grib2
使用如下
print “processing [shortName]”;
if(shortName == “u”){
print “shortName”;
}
会提示：
$ grib_filter rules.filter uv500.grib2
processing u
ERROR: Invalid key type
不知道原因，是否if中无法比较字符串？因为改成数字就正确
1.3.7. switch语句
Switch statement
if-else语句的替换版本
在需要从多个选项中选择时十分方便
语法：
switch (var) {
case val1:
# set of actions
case val2:
# set of actions
…………………………...
default:
# default block of actions
}
例10：
print "processing [paramId] [shortName] [stepType]";
switch (shortName) {
case "tp" : set stepType="accum";
case "sp" : set typeOfLevel="surface";
default: print "Unexpected parameter";
}
write;
例11：
if (centre is "lfpw" &&
(indicatorOfParameter == 6 ||
indicatorOfParameter == 11 ||
indicatorOfParameter == 8) )
{
if (step!=0 ) {
set typeOfGeneratingProcess=0;
set typeOfProcessedData=0;
} else {
# Other steps
set typeOfProcessedData=1;
…
switch (typeOfLevel) {
case "hybrid":
set changeDecimalPrecision=1;
case "surface":
set shortName="2t";
set changeDecimalPrecision=2;
case "isobaricInhPa":
if (level > 300) {
print "level > 300";
set level = level*2 + 15;
} # end if (level > 300)
default:
print "Unknown level type!";
} # end switch (typeOfLevel)
} # end if (step!=0)
write;
} # end main if
1.4. 练习
略
