Chapter 3. The Environmental Sensors – The Weather Utility App

In this chapter, we will learn how to make use of different types of sensors in our weather utility application. We will also look at how the temperature, relative humidity, and pressure sensor values can be extended to get more useful data such as the altitude, dew point, and absolute humidity. We will explore an alternate source for getting the temperature, relative humidity, and pressure values to compensate for the unavailability of any environment sensor on the phone.

The things you will learn in the this chapter are as follows:

• Understanding the requirements for the weather utility app
• Understanding environmental sensors (temperature, humidity, and pressure)
• How to use the temperature sensor of the phone
• Getting pressure sensor values and calculating the altitude using them
• Getting the relative humidity from the phone sensor and calculating the dew point and absolute humidity using the relative humidity and temperature sensor...

The weather utility app's requirements

Today's Android phones come with environment sensors in them. We will be using the same environment sensors to develop a weather utility app as a part of this chapter. Our app will make use of some additional inputs from external web services combined with our environment sensor's data to drive some more meaningful information, such as dew point, absolute humidity, and altitude. We will also compare weather data obtained from environment sensors to weather data obtained from an external web service. The following are high-level requirements for weather utility apps. The source code of this weather utility app can be found in GitHub under the author's account name and on the support page for the book:

1. Get the outside temperature using the phone's temperature sensor.
2. Get the air pressure using the phone's pressure sensor.
3. Calculate the altitude using the phone's pressure sensor.
4. Get the relative humidity using the phone's humidity sensor.
5. Calculate the dew...

Understanding environmental sensors

Environment-based sensors measure environmental conditions (temperature, humidity, and pressure) around the phone and report values only in one dimension (only one value in the values[] array). Temperature and humidity sensors have an on-change reporting mode, that is, they will report values whenever there is a change in values from the last reported values, whereas the pressure sensor has a continuous reporting mode; that is, it will report values continuously as per the suggested time interval. Environmental sensors are hardware-based and are only available if a device manufacturer has built them into a device. Because of this, it's particularly important that you verify, at runtime, that an environment sensor exists before you attempt to acquire data from it. Also, unlike motion sensors and position sensors, which often require high-pass or low-pass filtering, environment sensors do not typically require any data filtering or data processing:

• The temperature...

Time for action – using the temperature sensor

In this section, we will get the ambient temperature from the phone temperature sensor and will show it in the foreground activity. Before accessing the value for ambient temperature, we will also check the availability of the temperature sensor on the device.

1. We created a TemperatureActivity and implemented it with the SensorEventListener interface so that it receives the ambient temperature values. We are also checking if the ambient temperature is available on the device and are maintaining the availability state using the isSensorPresent Boolean variable. If the temperature sensor is not present, then we show the relevant message using  TextView. The following code snippet shows the necessary steps:

           public class TemperatureActivity extends Activity 
           implements SensorEventListener{ 
    
             private SensorManager mSensorManager; 
             private Sensor mSensor; 
             private boolean isSensorPresent...

Getting air pressure from the phone's pressure sensor

The procedure to get values from the phone's pressure sensor is exactly the same as the previous example showing getting values from temperature sensors. The only difference is the sensor type. To get values from the pressure sensor, we have to specify the sensor type as TYPE_PRESSURE. All other best practices (initiating SensorManager, the Sensor object, and registering and unregistering the listener and sensor callback) remain the same as they were in the previous temperature sensor example.

Time for action – calculating the altitude using the pressure sensor

Once we have atmospheric pressure from the phone's pressure sensor, we can calculate the altitude of the phone using the getAltitude(float p0, float p1) method of the SensorManager class. The first parameter of the altitude API is the atmospheric pressure at sea level, and the second parameter is the atmospheric pressure of the current location, which can be obtained from the phone...

Getting relative humidity from the phone's humidity sensor

Getting values from the phone's relative humidity sensor is a very similar process to getting values from the temperature or pressure sensors. The only difference is in specifying the sensor type. To get the values from the relative humidity sensor, we have to specify the sensor type as TYPE_RELATIVE_HUMIDITY. All the other standard practices  (initiating SensorManager, the Sensor object, and registering and unregistering the listener and the sensor callback) remain the same. Another point to note is that humidity and relative humidity are used interchangeably; they both refer to the same value.

Time for action - calculating the dew point and absolute humidity

We can use the phone's relative humidity and temperature sensor to calculate the dew point and absolute humidity. Before calculating, let's look at the definition and formula of the dew point and absolute humidity.

• Dew Point: The dew point is the temperature at which a given volume...

Summary

In this chapter, we learned how to use various environment sensors. We also derived of altitude, absolute humidity, and dew point values using the temperature, pressure, and relative humidity sensors. We also looked at alternate sources (the openweathermap web service) to obtain the temperature, relative humidity, and pressure values to compensate for the non-availability of any environment sensor on the phone.

In the next chapter, we will learn how to use light and proximity sensors, and we will look at how they can be used in real-world applications.