Bureau of Meteorology weather data

From Sensors in Schools
Jump to navigation Jump to search

Overview

  • The aim of this lesson is to learn how to retrieve weather data from the Bureau of Meteorology (BOM) using an API (Application Programming Interface).
  • An API is simply a URL that will automatically request data from a server.
  • In this example we will extract rain data from the daily weather forecast.
  • The daily weather forecast includes rain forecast data up to 7 days in advance.
  • We will use this data for our smart rainwater tank.
  • Smart rainwater tanks need to know rain events up to 7 days in advance so that they can discharge tank water before a storm arrives.

Learning Objectives

  • Learn how to use the Developer tools in a Web Browser to find an API
  • Learn how to use an API with HTTP Request node in Node-Red
  • Learn how to extract data from a larger data sets using the function node
  • Learn how to prepare data for a chart node

Obtaining BOM rain forecast data

  • This lesson will demonstrate how to extract data from the Bureau of Meterology using an API (Application Programming Interface).

Find Bureau of Meteorology API for daily weather forecast data

  • Open a Web Browser.
  • Enter the search term weather.bom.gov.au

  • Select Melbourne VIC as the weather location.

  • Ensure that Development Tools is selected under Preferences for your Browser settings.
  • Under the Develop menu select Connect Web Inspector.
  • This will open up an addition window to show some of the inner-workings of the web page.

  • In the Development Tools window click on the Network Tab.
  • Refresh the web browser.
  • In the window on the left search for a file named daily
  • Daily holds data related to current and future weather forecasts including 7 day rain predictions.
  • You can scroll in the Previous window to see all the retrieved data presented in JSON format.

Retrieve BOM data using Node-Red HTTP-In node

  • Create a flow in Node-Red using the nodes:
    • Inject – timestamp
    • http request – this will request data using the daily API
    • debug – to display the output of the API in the debug window

  • Double click on the HTTP request node and enter the following details.
  • To copy the API request from the Web Browser use the right mouse button Copy function.
  • Paste the API into notepad or a text editor to ensure that it has copied correctly.
  • You may need to paste the API into a text editor on the Raspberry Pi.
  • Failing this, enter the API directly.
  • Ensure that the Return is a parsed JSON Object
  • Give the Name - BOM daily

  • Deploy the program then click on the input to the inject node to run the program.
  • The output should appear in the debug window on the right.
  • Click on the small expansion arrows to show more of the data content.

Collecting Day 0 rain data

  • Add a function node and debug node and arrange the nodes as shown below.

  • Double click on the function node and enter the following code.
  • The code will extract day 0 (zero) max rainfall and place it in the variable rain.
  • Name the function node Day 0 (zero) rain

  • Deploy the code.
  • Clear the Debug window and then click on the inject node to run the program.
  • Your output will be different because it will be based on the daily weather forecast.
  • This result shows that today (day 0) there will be a maximum of 2.2 mm of rain.

Collecting Day 1 rain data

  • Copy the Day 0 rain function node by entering the shortcut Ctrl+C
  • Enter Ctrl-V to paste a copy of the node.
  • Then double click on the new function node to edit it.

  • Change the Name property to Day 1 rain
  • Modify the code to the example shown below.
  • Notice that some descriptive text will be added to the msg.payload

  • Add another Debug node and connect the nodes as shown.
  • Some rearrangement of the nodes will help make the wires and flow clearer.

  • Deploy the flow.
  • Clear the Debug window. Click on the inject node to start the program.
  • Two outputs are presented.
  • One for Day 0 rain and the second for Day 1 rain.

Downloading all the rain data using a for loop

  • Modify the node-red flow to the following.

  • Double click on the function node.
  • Change the Name to 7 day rain
  • Enter the following code:
    • rainmax = [] – create a single variable called an array that will hold all the rain data. Think of it as rainmax[0] for the first data item, rainmax[1] for the second data item, etc
    • for(let i=0; i<8; i++) {} – this for loop initilises a counting variable i to zero (0). It tests to see if the counting variable is less than (<) 8. Each time the for loop goes around the counting variable i is increased by one (i++)
    • rainmax[i] = msg.payload.data[i] – in this statement think of the counting variable i being replaced with 0, 1,2, etc with every loop.
    • msg.payload = [{}] – the msg.payload needs to have data formatted correctly before it can be delivered to the chart node.

  • Double click on the Chart node.
  • From the Group select Add new ui_group
  • Then click on the Edit pen on the right.

  • In the Edit chart node > Add new dashboard group config node
  • In Tab select Add new ui_tab
  • Then click on the Edit pen

  • In the Add new dashboard tab config node
  • Enter the Name BOM rain and click Add

  • In the Add new dashboard group config node.
  • Ensure the Name and Tab are BOM rain and click Add

  • Back in the parent Edit chart node window.
  • Change from Line chart to Bar chart.

  • In the Edit chart node window change the Y-axis to min 0 and max 100

  • In the main editing window in Node-Red click on Deploy.
  • Click on the Inject node to generate data for the Chart.
  • In the web browser open a new tab and enter the URL localhost:1880/ui
  • Navigate to BOM rain
  • You should see the following chart.

Final improvement

  • Sometimes the BOM daily data set returns an array that is 7 or 8 elements long, depending on the time of day.
  • If the for loop asks to elements that don’t exist our program will generate an error.
  • One way to fix this is to find out how many elements are in the array using the built-in function length

Retrieved from "http://www.waterwaysinwhittlesea.org/index.php?title=Bureau_of_Meteorology_weather_data&oldid=952"