Selecting data

This command determines the data to be applied in subsequent input read or product generation commands.

In Rack, many operations implictly select a subset of available data instead of using it all. For example, in computing a Pseudo CAPPI image, DBZH data from single-PRF sweeps is used by default.

Synopsis

--select, -s  <selector>  (section: general)
  Data selector for the next computation
    selector=path,quantity,elangle,count,order,prf,timespan 

Remarks on the options:

path argument defines a path segment to be matched, with desired index ranges (example: dataset2:4/data3:8 )
in path argument, a leading slash fixes the matching to the root (example: /dataset:/data: ), otherwise the tail part is matched
quantity argument accepts a list of strings separated by semicolon ':'
each item in a quantity argument list can be a literal string like DBZH or a regular experession like ^DBZ[HV]?$

See example sets below!

This option is useful in selecting data for:

partial reading a large input file (see File input and output ).
a meteorological product (see Meteorological products ).
compositing (see Cartesian conversions and composites ).
saving images (PNG, GeoTIFF, PPM; see Image processing ).
other data dumps, useful in debugging, for example

The following command lines illustrate usage of –select in product generation and image output.

# For a Pseudo CAPPI product, change default input selection
rack volume.h5 --select 'quantity=^TH$,elangle=1.5:10,count=3' --pCappi 1500 -o pCappi-TH-1500m.h5
 
# For image output, select DBZH  
rack volume.h5 --select elangle=1.5,quantity=DBZH -o volume-DBZH.png
 
# For image output, select VRAD of the lowest dual-PRF scan 
rack volume.h5 --select quantity=VRAD:VRADH,order=ELANGLE:MIN,prf=DOUBLE -o volume-VRAD.png
 
# For image output, select ZDR of the highest single-PRF scan 
rack volume.h5 --select quantity=ZDR,count=1,order=ELANGLE:MAX,prf=SINGLE -o volume-ZDR.png
 
# For single-image output, select DBZH of the lowest scan (from 90 6.5 2.4 1.8 1.2 0.59)
rack volume.h5 --select quantity=DBZH,order=ELANGLE:MIN -o volume-DBZH2.png
 
# For single-image output, select dBZ - preferably total dBZ - of the highest scan (from 90 6.5 2.4 1.8 1.2 0.59)
rack volume.h5 --select quantity=TH:TV:T:DBZH:DBZ,order=ELANGLE:MAX -o volume-DBZH3.png
 

The following examples are less realistic than those above, but are used in unit testing of the program code.

# Index range: select dataset3, including its subgroups. 
rack volume.h5 --select /dataset3 -o volume-select.txt
 
# Index range: select DATASET groups with index 2...5, including subgroups. 
rack volume.h5 --select /dataset2:5 -o volume-select.txt
 
# Index range test: select DATASET groups with index 3 at least.
rack volume.h5 --select /dataset3: -o volume-select.txt
 
# Index range test: select DATASET groups with index 3 at largest. 
rack volume.h5 --select /dataset:3 -o volume-select.txt
 
# For text output, select paths ENDING with 'what', 'where', or 'how'. 
rack volume.h5 --select 'what|where|how' -o volume-select.txt
 
# For text output, select paths of elevations of at least 6.0 degrees 
rack volume.h5 --select elangle=6.0 -o volume-select.txt
 
# For text output, select paths of elevations up to 6.0 degrees 
rack volume.h5 --select elangle=:6.0 -o volume-select.txt
 
# For text output, select 'where' groups of 3 lowest elevations from 0.5 degrees upwards 
rack volume.h5 --select where,elangle=0.5:90.0,count=3 -o volume-select.txt
 
# For text output, select 'what' and 'where' groups of elevations from 0.5 to 6.0 degrees
rack volume.h5 --select 'what|where,elangle=0.5:6' -o volume-select.txt
 
# Select a unique quality field
rack volume.h5 --select quantity=CLASS-ETOP -o volume-select.txt
 
# Select all QIND fields
rack volume.h5 --select quantity=QIND -o volume-select.txt
 
# Select global (dataset-level) QIND fields
rack volume.h5 --select quantity=/QIND -o volume-select.txt
 
# Select quantity-specific (data-level) QIND fields
rack volume.h5 --select quantity=.+/QIND -o volume-select.txt
 
# Select quantity-specific (data-level) QIND field
rack volume.h5 --select quantity=DBZ-SLOPE-SMOOTH/QIND -o volume-select.txt
 
# Select non-existing quantity-specific QIND field
rack volume.h5 --select quantity=HGHT/QIND -o volume-select.txt
 

See also: CmdDelete; CmdKeep; CmdSetODIM; rack::CmdSelect (code); rack::DataSelector (code)

Table of Contents

Selecting data