title: Three.js Calculate the Area of Geometry Face (Face3)
body: <p>I am exporting a 3D model with the ColladaLoader, every Mesh create a Geometry object with multiple Faces.</p>
  
  <p>I manage to select faces to change colors and textures of a single face that is an array of Triangles (Face3).
  <a href="https://i.stack.imgur.com/81uOX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/81uOX.png" alt="Change color of single face of a Mesh"></a></p>
  
  <p><a href="https://i.stack.imgur.com/z6Q3a.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z6Q3a.png" alt="Change texture of single face of a Mesh"></a></p>
  
  <p>Know I need to get the area of each "Face" I know the faces are a sum of Triangles instances of Face3. I try looping through each related face and summing the <strong>a, b and c</strong> values like this, but with no luck.</p>
  
  <pre><code>var sAB = Math.abs(face.a - face.b);
  var sBC = Math.abs(face.b - face.c);
  var sCA = Math.abs(face.c - face.a);
  var s = sAB + sBC + sCA;
  var a = Math.sqrt(s*(s-sAB)*(s-sBC)*(s-sCA));
  </code></pre>
  
  <p>How can a calculate the Area of a Face3 triangle object?</p>