Writing a WDSSII Application using w2algcreator

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Writing a WDSS-II Applicationusing w2algcreator

• V Lakshmanan
• National Severe Storms Laboratory University of
  Oklahoma
• lakshman_at_ou.edu

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WDSS-II application development

• WDSS-II provides a easy environment to develop
  new applications or algorithms.
• Any algorithm developed in WDSS-II can be run
  either in archive mode or in real-time.
• provided that the algorithm is fast enough to run
  in real-time and the machine can handle it!

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WDSS-II for Applications

• What does WDSS-II provide your application?
• Easy ingest of data from multiple sensors
• Easy ways to write out and visualize intermediate
  and final outputs.
• A common framework for accessing data.
• The framework is written in C.
• Its best if you can write your code in C too.
• But you can call Fortran or C code from C

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Creating a new application

• WDSS-II has a tool to create a new application
  quickly.
• w2algcreator
• Need to create an input XML file specifying the
  inputs to your application.
• Will create C main and a template for your
  scientific code.
• Your then write the scientific code.

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How WDSS-II works

• WDSS-II applications connect to a source of data.
• Called an Index.
• Applications listen for new products in that
  Index.
• Decide whether or not to process that product.
• Create and process the data if needed.
• Write out outputs (in netcdf or XML).
• Notify an Index about the new products available.
• For other applications listening to that Index
• May be a different index from the source.

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WDSS-II Applications

• WDSS-II Applications are just executables.
• launched on the command line.
• In deployed systems through scripts.
• Inputs are specified on the command-line.

w2vil i xmllb/data/realtime/radar/KTLX/code_inde
x.lb \ -R ReflectivityQC \ -o
/data/realtime/radar/KTLX/ \ -r
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Command-line options

• w2vil algorithm executable name
• VerticalIntegratedLiquid algorithm full name
  (used in source code)
• Input RadarIndex specified by i option
• Input data type is specified by R option
• Output directory is specified by o option
• Real-time is specified by r option
• The options r, -l (the letter ell), -o are
  reserved so that the deployment scripts work
  correctly.

• w2vil i xmllb/data/realtime/radar/KTLX/code_inde
  x.lb \
• -R ReflectivityQC \
• -o /data/realtime/radar/KTLX/ \
• -r

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Some conventions

• If you need to provide domain extents, use the
  following letters
• t top to specify the north-west-top corner
• b bottom to specify the south-east-bottom
  corner
• s to specify the grid spacing
• If you need to process only a certain sub-type,
  use colons as a separator
• -R ReflectivityQC00.50
• -R ReflectivityMaximumvol

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Creating a new application

• Need to create an XML file.
• Use your favorite text editor. Save it somewhere.
• A template is available as example_alg.xml you
  can edit this if you want.
• What is the algorithms descriptive name?
• Used to generate class names in template.
• What is the executable name?
• What is the namespace that generated code should
  be in? Pick your group (casa) or name (tj) i.e.
  something that will distinguish your code from
  something someone else might create.

ltalgorithmcreator nameVerticalIntegratedLiq
uid execw2vil namespacew2polargt lt/algori
thmcreatorgt
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Inputs

• Next you need to specify inputs.
• Done within an inputs section.
• How many indexes do you need to connect to?
• Each index or group of indexes will get a new
  index tag.
• Give each index a name (RadarIndex, ModelIndex,
  etc.) so that a user can understand what needs to
  be provided to your algorithm.
• Supply a mnemonic option letter as well.
• The most important input index is by convention
  given the option letter i.
• Specify the history (in minutes) that needs to be
  maintained for each index (or group of indexes).
• Can be just 1 minute if you will never search
  backwards in your algorithm (only new data).

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Input Index specification
ltalgorithmcreator . gt ltinputsgt ltindex
history5gt ltoptionvalue
nameRadarIndexes
letteri /gt lt/indexgt ltindex gt
. lt/indexgt lt/inputsgt lt/algorithmcreatorgt
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Input Data specification

• The user may specify either just a single index
  or a bunch of index URLs. So each index tag
  actually corresponds to a group of indexes in
  general.
• For each index, specify the data that you will be
  listening to in that index.
• For each product listened to, specify
• How you will refer to the product (e.g dbz)
• The default name of the product (e.g
  ReflectivityQC)
• This is the official name of the product that
  you can see on the display.
• A mnemonic letter for this input
• What type of data is it? WDSS-II data are usually
  one of these types
• RadialSet
• LatLonGrid
• LatLonHeightGrid
• DataTable

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Input Data Specification

• ltindex history5gt
• ltoptionvalue . /gt
• ltdata typeRadialSetgt
• ltoptionvalue namedbz
• letterR
• defaultReflectivityQC
  /gt
• lt/datagt
• ltdata gt
• lt/datagt
• lt/indexgt

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Option

• The optionvalue tag
• Has a letter, name and default
• The default tag is optional if you leave it out
  the user has to specify a value on the
  command-line.
• If the default is false, then the option is a
  boolean option i.e. yes/no.

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Optional data

• To specify an optional index, specify that the
  default value is an empy string.
• E.g. you will use a model index if one is
  available, otherwise, you will run only on radar
  data.
• You need to specify a default name for all input
  data types
• otherwise we wont know what to listen for.

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Other options

• Besides the input, do you need any other
  parameters specified for your algorithm?
• For example, maybe you need to know the radar
  name.
• For each such option
• Specify the name of the option (e.g RadarName)
• Specify a mnemonic (e.g S for sourceRadar,
  since r and R are both taken by realtime and
  Reflectivity respectively )

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Other options

• ltalgorithmcreator gt
• ltoptionsgt
• ltoptionvalue letters
• namesourceRadar /gt
• ltoptionvalue /gt
• lt/optionsgt
• lt/algorithmcreatorgt

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Use the w2algcreator

• Now that you have the XML file
• Run the w2algcreator program
• It will create a w2vil_main.cc and
  w2vil_VerticalIntegratedLiquid.h file in the
  output directory.
• Plug in the code for the two functions specified
  in the .h file
• One function tells you the radar name, the output
  directory to write your outputs to and the LB to
  notify after you have written the outputs.
• The other function is called processdbz()
• Your scientific code goes in there.

w2algcreator i name-of-your-XML-file
-o output-directory
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Final steps

• Fill in the scientific code.
• Compiling
• Use the example_Makefile that is provided to
  compile and link against the WDSS-II libraries.
• Or put your source code into a subdirectory of
  the w2algs repository
• Need to create Makefile.am
• See w2algs/w2algcreator/README for details.

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The autogenerated code

• What does the autogenerated code do?
• It creates listeners to listen for the products
  your algorithm needs
• The user tells the algorithm the Index where
  those products may be found
• Also specifies that ReflectivityQC_smoothed
  should be used where your algorithm expects a
  reflectivity
• May tell your algorithm to provide heartbeat
  messages
• The code has fault handling
• If you lose connection to an Index on a remote
  machine, the algorithm will reconnect.
• If your algorithm hangs or starts to eat up the
  CPU, itll stop providing heartbeat messages,
  thus allowing an external monitoring program to
  kill it and restart it.
• A good idea to specify initOnStarttrue for any
  product that should re-read if your algorithm is
  restarted.
• As soon as it receives notification of a product,
  it tells your algorithm class about it
• Then, you do your thing!

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On a timer

• W2algcreator is for data-driven applications
• Best to process data as it comes in
• So, design your application to be data-driven as
  much as possible.
• To do things on a timer
• Use a TimedEventHandler (see API documentation)
• Provide a listener that will be called every N
  milliseconds.

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Exercises

• The best way to learn is to write simple
  data-driven algorithms.
• The next module on data formats will help you
  accomplish these tasks.
• May need to get input data from some source
  first.
• These examples should get you started
• Read in single-radar reflectivity data and write
  out an indexed scan with values below a
  user-defined threshold set to MissingData.
• Hint PolarGrid is an indexed RadialSet
• User-defined implies you need a command-line
  parameter
• Use ProcessTimer to determine how long certain
  steps take.
• Read in both reflectivity and velocity data from
  the same radar and index the reflectivity data at
  the velocity azimuths.
• You will need to operate with RadialSet data
• Wait for matching Reflectivity and Velocity scans
  (use the elevation angle to check)
• Form a histogram of VIL values to satellite IR
  temperatures.
• Use DataConverter and/or DataRemapper
• A multi-source algorithm. Makes a difference only
  when running, not when writing the algorithm!

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Questions?

• Email me
• lakshman_at_ou.edu
• More documentation (including a more up-to-date
  version of this document) is at
• http//www.wdssii.org/