Forecast element API

On the client/server side the API is exposed using the Feathers isomorphic API and the Feathers common database query API

Forecast model instances expose each element found in configuration through a service named forecast.name/element.name implementing the Feathers service interface for CRUD. Although only web sockets are usually used on the client side by default, both the REST and the Socket interfaces are configured.

create, update, patch, remove methods are only allowed from the server side, clients can only getand find forecast elements.

Each forecast model instance exposes each element service using a database adapter as an implementation of the Feathers service interface. Because we want to remain database-agnostic, just like Feathers is, the database adapter to be used is only known at startup depending on your configuration. That's the reason why there is no static forecast element class in the core of Weacast, instead it provides a set of functional mixins that will be applied on the instancied element service and are described hereafter.

Data model

The common data model of a forecast element as used by the API is detailed here.

Forecast element data are usually large so they are not returned by default, , you have to explicitely ask for using $select

Available forecast data

For exemple you can request the available forecast data for a given element like this:

import api from 'src/api'

api.getService(forecast.name + '/' + element.name).find()
.then(response => {
  // Do something with the element data
})

Response:

{
  "total": 27,
  "limit": 10,
  "skip": 0,
  "data": [
    {
      "_id": "59144a3ed0c0a234f8b4f86d",
      "runTime": "2017-05-11T06:00:00.000Z",
      "forecastTime": "2017-05-11T19:00:00.000Z",
      "minValue": -10.490379333496094,
      "maxValue": 15.306495666503906
    },
    {
      "_id": "59144ab0d0c0a234f8b4f88b",
      "runTime": "2017-05-11T06:00:00.000Z",
      "forecastTime": "2017-05-12T00:00:00.000Z",
      "minValue": -10.069664001464844,
      "maxValue": 11.477210998535156
    }
  ]
}

Property selection

You can skip pagination and retrieve selected properties only:

import api from 'src/api'

api.getService(forecast.name + '/' + element.name).find({
  query: {
    $paginate: false,
    $select: ['forecastTime']
  }
})
.then(response => {
  // Do something with the element data
})

Response:

[
  {
    "_id": "59144a3ed0c0a234f8b4f86d",
    "forecastTime": "2017-05-11T19:00:00.000Z"
  },
  {
    "_id": "59144a83d0c0a234f8b4f881",
    "forecastTime": "2017-05-11T22:00:00.000Z"
  },
  {
    "_id": "59144a95d0c0a234f8b4f886",
    "forecastTime": "2017-05-11T23:00:00.000Z"
  }
 ]

Data retrieval

To retrieve data for a given time you have to request it explicitely:

import api from 'src/api'

api.getService(forecast.name + '/' + element.name).find({
  query: {
    time: new Date().toISOString(),
    $select: ['forecastTime', 'data']
  }
})
.then(response => {
  // Do something with the element data
})

Response:

{
  "total": 1,
  "limit": 10,
  "skip": 0,
  "data": [
    {
      "_id": "59144a3ed0c0a234f8b4f86d",
      "forecastTime": "2017-05-11T19:00:00.000Z",
      "data": [ ... ]
     }
   ]
 }

When no more query parameters are provided the data retrieved are the ones at the original resolution of the model. If you want to resample data at a lower resolution to improve bandwidth and performance you could add the target grid configuration as parameters:

import api from 'src/api'

api.getService(forecast.name + '/' + element.name).find({
  query: {
    time: new Date().toISOString(),
    $select: ['forecastTime', 'data'],
    oLon: origin[0],
    oLat: origin[1],
    sLon: size[0],
    sLat: size[1],
    dLon: resolution[0],
    dLat: resolution[1],
  }
})
.then(response => {
  // Do something with the element data
})

where:

  • origin is the geographical origin of the target data grid as an array of decimal values [longitude origin, latitude origin],
    • size is the size of the target data grid as an array of integer values [width, height],
    • resolution is the geographical resolution of the target data grid as an array of decimal values [longitude resolution, latitude resolution]

Tiles

When tiling is enabled you can retrieve element tiles instead of the whole forecast data when you'd like to know what occurs in a given area or at a given location. Because tiles have an indexed geometry property you can perform a geospatial query.

If you also configured your element services to generate tiles with aggregated data over all forecast times you can select it by querying with the following additional field: { timeseries: true }.

Base element mixin source

This mixin includes the most basic functions shared by all forecast elements

.getNearestRunTime(datetime)

Returns the nearest weather prediction model run date/time for a given date/time, it basically rounds the hours according to the runInterval value in the model configuration.

.getNearestForecastTime(datetime)

Returns the nearest weather prediction model forecast date/time step for a given date/time, it basically rounds the hours according to the interval value in the model configuration.

Refresh element mixin source

This mixin includes the most basic functions shared by all forecast elements to help updating forecast data from providers.

.getDataDirectory()

Returns the path where downloaded/persisted data are located for the element

async .updateForecastData(mode)

Launches the forecast data update process for the element depending on the mode value:

  • 'once' : will perform data update for the current time only
  • 'interval' : will perform data update for the current time and schedule the update process at regular interval after each data gathering according to the updateInterval value in the model configuration.

async .refreshForecastData(datetime)

Refreshes forecast data for the element based on the nearest run for the provided date/time. It will harvest data for each forecast time step available in the model according to the lowerLimit/upperLimit values in the model configuration.

async .harvestForecastTime(datetime, runTime, forecastTime)

Refreshes forecast data for the element based on the provided run and forecast date/time. If the run is not yet available through the provider it will try to use the previous one until the oldestRunInterval value in the model configuration is reached.

async .refreshForecastTime(datetime, runTime, forecastTime)

Download the forecast data for the given run/forecast date/time and process it, i.e. convert it if required then store it in the database.

async .downloadForecastTime(runTime, forecastTime)

Download the forecast data for the given run/forecast date/time and returns the file path to the downloaded data.

Forecast element hooks

The following hooks are executed on each Forecast element service: Element hooks

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