Merge pull request #30 from natemara/master

Add Altimeter trait and default implementaiton

Author: posborne

src/sensors/mod.rs

@@ -37,8 +37,7 @@ pub trait Thermometer {
 
  /// Get a temperature from the sensor in degrees celsius
  ///
- /// Returns Some(temperature) if available, otherwise returns
- /// None
+ /// Returns `Ok(temperature)` if available, otherwise returns `Err(Self::Error)`
  fn temperature_celsius(&mut self) -> Result<f32, Self::Error>;
 }
 
@@ -48,7 +47,31 @@ pub trait Barometer {
 
  /// Get a pressure reading from the sensor in kPa
  ///
- /// Returns Some(temperature) if avialable, otherwise returns
- /// None
+ /// Returns `Ok(temperature)` if avialable, otherwise returns `Err(Self::Error)`
  fn pressure_kpa(&mut self) -> Result<f32, Self::Error>;
 }
+
+/// Trait for sensors that provide access to altitude readings
+pub trait Altimeter {
+ type Error: Error;
+
+ /// Get an altitude reading from the sensor in meters, relative to the pressure in kPa at
+ /// sea level
+ ///
+ /// Returns `Ok(altitude)` if available, otherwise returns `Err(Self::Error)`
+ fn altitude_meters(&mut self, sea_level_kpa: f32) -> Result<f32, Self::Error>;
+}
+
+impl<T> Altimeter for T
+ where T: Barometer
+{
+ type Error = <Self as Barometer>::Error;
+
+ fn altitude_meters(&mut self, sea_level_kpa: f32) -> Result<f32, Self::Error> {
+ let pressure = try!(self.pressure_kpa()) * 1000.;
+ let sea_level_pa = sea_level_kpa * 1000.;
+
+ let altitude = 44330. * (1. - (pressure / sea_level_pa).powf(0.1903));
+ Ok(altitude)
+ }
+}