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README.md

Pegel Alarm

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This repository contains the source for the Android application Pegel Alarm. Pegel Alarm helps people living in areas affected by floodings in Germany by providing alarms whenever rivers haven rise above user defined thresholds. For more info please visit http://pegelalarm.de/ (in German).

App setup

To get started with Pegel Alarm, you will first need to head over to the Google Developer Console, create a new project and enable the following APIs:

  • Google Cloud Messaging for Android
  • Google+ API

In addition you will need to setup 2 OAuth client ids, one for Pegel Alarm and one for the backend services (ODS + CEPS, see below).

Next head over to your local copy of the Pegel Alarm source and add the following string defintions, typically under app/src/main/res/values/config.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="google_project_id">...</string>
    <string name="google_oauth_web_client_id">...</string>
    <string name="ods_base_url">https://ods.cs.fau.de/ods/api/v1</string>
    <string name="ceps_base_url">https://ods.cs.fau.de/ceps/api/v1</string>
    <string name="google_analytics_property_id">...</string>
</resources>
  • google_project_id: the id of the project you created above
  • google_oauth_web_client_id: the id of the web (!) oauth client you created above

Backend setup

Pegel Alarm uses a number of backend services to get the job done, most notably the Open Data Service (ODS) and the Complex Event Processing Service (CEPS). Both need some configuration in order to work with Pegel Alarm.

ODS setup

The ODS is responsible for fetching and providing water related data from various sources, such as PegelOnline. In order for the ODS to start pulling this data, the following source needs to the added to the ODS (see the ODS docs for more info about how to add sources):

  • name: pegelalarm
  • domainIdKey: /gaugeId
  • schema:
{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "type": "object",
    "properties": {
      "gaugeId": {
        "type": "string"
      },
      "name": {
        "type": "string"
      },
      "km": {
        "type": "number"
      },
      "agency": {
        "type": "string"
      },
      "longitude": {
        "type": "number"
      },
      "latitude": {
        "type": "number"
      },
      "water": {
        "type": "string"
      },
      "currentMeasurement": {
        "type": "object",
        "properties": {
          "timestamp": {
            "type": "string"
          },
          "value": {
            "type": "number"
          },
          "trend": {
            "type": "integer"
          },
          "stateMnwMhw": {
            "type": "string"
          },
          "stateNswHsw": {
            "type": "string"
          },
          "characteristicValues": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "shortname": {
                  "type": "string"
                },
                "longname": {
                  "type": "string"
                },
                "unit": {
                  "type": "string"
                },
                "value": {
                  "type": "integer"
                },
                "validFrom": {
                  "type": "string"
                },
                "timespanStart": {
                  "type": "string"
                },
                "timespanEnd": {
                  "type": "string"
                },
                "occurrences": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  }
                }
              }
            }
          }
        }
      }
    }
  }

This will create a source object on the ODS but does not yet start pulling data from anywhere. To do that you will need to add a filter chain to the newly created source. The body usually looks like this:

{
  "processors" : [
    {
      "name" : "JsonSourceAdapter",
      "arguments" : {
        "sourceUrl" : "http://pegelonline.wsv.de/webservices/rest-api/v2/stations.json?includeTimeseries=true&includeCurrentMeasurement=true&includeCharacteristicValues=true"
      }
    },
    {
      "name" : "PegelOnlineMerger",
      "arguments" : { }
    },
    {
      "name" : "DbInsertionFilter",
      "arguments" : {
        "updateData" : true
      }
    },
    {
      "name" : "NotificationFilter",
      "arguments" : { }
    }
  ],
    "executionInterval" : {
    "period" : 1,
    "unit" : "MINUTES"
  }
}

CEPS setup

The CEPS is responsible for tracking and evaluting user defined rules and uses the ODS as a basis for data. In the case of Pegel Alarm the CEPS handles rules which trigger whenever water levels have risen above or below user defined thresholds. If such an event is triggered it will use Google Cloud Messaging (GCM) to notify the corresponding Android device about the news.

By default the CEPS does not know anything about the ODS and hence needs to be configured to receive data from it. This is done by adding a source with the same id as on the ODS to CEPS, so in our case pegelalarm.

Next the CEPS requires two EPL (event processing language) adapters which represent the "rules" that clients of the CEPS can use. The adpaters are:

  • pegelAlarmAboveLevel with a body of
{
    "eplBlueprint": "select station1, station2 from pattern [ every station1=`pegelalarm` ( gaugeId = 'GAUGE_ID' ) -> station2=`pegelalarm` ( gaugeId = 'GAUGE_ID' ) ] where station1.currentMeasurement.value <= LEVEL and station2.currentMeasurement.value > LEVEL",
    "requiredArguments": {
        "GAUGE_ID": "STRING",
        "LEVEL": "NUMBER"
    }
}
  • pegelAlarmBelowLevel with a body of
{
    "eplBlueprint": "select station1, station2 from pattern [ every station1=`pegelalarm` ( gaugeId = 'GAUGE_ID' ) -> station2=`pegelalarm` ( gaugeId = 'GAUGE_ID' ) ] where station1.currentMeasurement.value >= LEVEL and station2.currentMeasurement.value < LEVEL",
    "requiredArguments": {
        "GAUGE_ID": "STRING",
        "LEVEL": "NUMBER"
    }
}

License

Copyright 2014 Philipp Eichhorn
Copyright 2014, 2015 Friedrich-Alexander Universität Erlangen-Nürnberg

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see http://www.gnu.org/licenses/.