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1. The bufr_filter processes sequentially all bufr messages contained in the input files and applies the rules to each one of them. Input messages can be written to the output by using the "write" statement. The write statement can be parameterised so that output is sent to multiple files depending on key values used in the output file name. If we write a rules_file containing the only statement:

   Code Block
   write "../data/split/[bufrHeaderCentre:l]_[dataCategory].bufr[editionNumber]";

   Applying this rules_file to the "../data/bufr/mutitype.bufr" bufr file we obtain several files in the ../data/split directory containing messages split according to their key values

   Code Block
   > bufr_filter rules_file ../data/bufr/multitype.bufr > ls ../data/split 98_0.bufr3 98_5.bufr3 ecmf_3.bufr4




2. Bufr The bufr header information can be accessed without unpacking the data. This rules_file:

   Code Block
   print "[bufrHeaderCentre] [bufrHeaderSubCentre] [masterTablesVersionNumber] [localTablesVersionNumber] [numberOfSubsets]";

   will result in the following output:

   Code Block
   > bufr_filter rules_file ../data/bufr/syno_multi.bufr 98 0 13 1 1 98 0 13 1 1 98 0 13 1 1




3. To print values from the data section the messages have to be unpacked. To do that we need to set key unapck unapack to 1. This rules_file:

   Code Block
   set unpack=1; print "block=[blockNumber] station=[stationNumber] lat=[latitude] lon=[longitude] t2=[airTemperatureAt2M]";

   will print out some data values from the specified SYNOP bufr messages.

   Code Block
   > bufr_filter rules_file ../data/bufr/syno_multi.bufr block=1 station=1 lat=70.93 lon=-8.67 t2=274.5 block=1 station=3 lat=77 lon=15.5 t2=268.4 block=1 station=7 lat=78.92 lon=11.93 t2=268.5




4. bufr_filter allows defining new keys with the transient keyword. We will further develop the previous example by creating a new key to combine the block number and the station number into the full WMO station id:

   Code Block
   set unpack=1; transient statid=1000*blockNumber+stationNumber; print "statid=[statid] lat=[latitude] lon=[longitude] t2=[airTemperatureAt2M]";

   The result is:

   Code Block
   > bufr_filter rules_file ../data/bufr/syno_multi.bufr statid=1001 lat=70.93 lon=-8.67 t2=274.5 statid=1003 lat=77 lon=15.5 t2=268.4 statid=1007 lat=78.92 lon=11.93 t2=268.5




5. We can use conditional statements in bufr_filter. The syntax is: \

   Code Block
   if ( condition ) { block of rules } else { block of rules }

   The condition can be made using ==,!= and joining single block conditions with || and &&. The statement can be any valid statement also another nested condition For example the The rules_file below will shows us how to filter only SYNOP messages with a specific station id:

   Code Block
   set unpack=1; transient statid=1000*blockNumber+stationNumber; if (dataCategory ==0 && statid == 1003) { write out.bufr; }




6. The switch statement is an enhanced version of the if statement. Its syntax is the following:

   Code Block
   switch (key1,key2,...,keyn) { case val11,val12,...,val1n: # block of rules; case val21,val22,...,val2n: # block of rules; default: # [ block of rules ] }

   Each value of each key given as argument to the switch statement is matched against the values specified in the case statements. If there is a match, then the block or rules corresponding to the matching case statement is executed. Otherwise, the default case is executed. The default case is mandatory, even if empty. The "~" operator can be used to match "anything".




7. To access the keys' attributes belonging to the keys use the -> operator. The example below prints the attributes of key "pressure" from a SYNOP bufr message.

   Code Block

   print "pressure=[pressure] [pressure->units]"; print "pressure->code=[pressure->code!06d]"; print "pressure->scale=[pressure->scale]"; print "pressure->reference=[pressure->reference]"; print "pressure->width=[pressure->width]"; print "pressure->percentConfidence=[pressure->percentConfidence] [pressure->percentConfidence->units]"; print "pressure->percentConfidence->code=[pressure->percentConfidence->code!06d]"; print "pressure->percentConfidence->scale=[pressure->percentConfidence->scale]"; print "pressure->percentConfidence->reference=[pressure->percentConfidence->reference]"; print "pressure->percentConfidence->width=[pressure->percentConfidence->width]";

   The result is:

   Code Block
   > bufr_filter rules_file ../data/bufr/syno_1.bufr pressure=100910 Pa pressure->code=010004 pressure->scale=-1 pressure->reference=0 pressure->width=14 pressure->percentConfidence=74 % pressure->percentConfidence->code=033007 pressure->percentConfidence->scale=0 pressure->percentConfidence->reference=0 pressure->percentConfidence->width=7




8. To access elements keys by rank (i.e. by their occurrence in the message) use the # operator. The example below prints the 4th value of key "pressure" from a TEMP bufr message. As a reference, we also print all the pressure values found in the message.

   Code Block
   set unpack=1; print "pressure=[pressure#4] [pressure#4->units]"; print "pressure=[pressure]";

   The result is:

   Code Block

   > bufr_filter rules_file ../data/bufr/temp_101.bufr pressure=98500 Pa pressure=102000 101800 100000 98500 96400 92500 92100 89700 88100 86100 85000 84400 79400 79000 78300 77300 71900 70000 69400 65100 61200 53400 50000 43900 40000 39900 37800 31600 30000 27500 25000 21200 21000 20600 20400 20000 19300 18400 17000 16600 15100 15000 14600 14000 13400 13200 12900 11100 10800 10000 8960 7630 7000 6420 6190 5770 5320 5000 3970 3570 3190 3090 3000 2820 2630 2400 2340 2050 2000 1680 1530 1500 1380 1300 1210 31600




9. It is possible to access elements by conditions imposed on coordinate descriptors. The example below prints the temperature values on temperature significant levels from a TEMP bufr message. For temperature significant levels the key "verticalSoundingSignificance"=4 and this is what we use in the condition. :

   Code Block
   set unpack=1; print "----- /verticalSoundingSignificance=4/airTemperature -----"; print "[/verticalSoundingSignificance=4/airTemperature]";

   The result is:

   Code Block

   > bufr_filter rules_file ../data/bufr/temp_101.bufr ----- /verticalSoundingSignificance=4/airTemperature ----- 272.1 269.5 268.1 267.9 266.7 266.1 264.9 264.9 260.5 260.9 263.5 263.7 261.7 261.9 259.1 258.9 251.5 243.9 238.3 236.7 221.7 212.7 215.5 215.9 214.1 217.3 218.3 217.3 219.3 218.9 219.5 217.9 218.3 217.5 220.3 219.1 220.1 217.3 216.5 217.7 215.9 217.1 213.5 216.1 214.7 216.1 215.3 216.5 213.9 215.3 215.7 212.7 214.1 216.1 213.7 215.3 214.9