Added a few methods to compute faces area

src/model.rs

@@ -211,6 +211,19 @@ impl Model {
         parse(path)
     }
 
+    /// Computes the area of a 3D face of the model.
+    pub fn face_area(&self, f: &Face) -> f64 {
+        self.face_vertex_area(&f.a, &f.b, &f.c)
+    }
+
+    /// Computes the 3D area of a face from 3 face vertices.
+    pub fn face_vertex_area(&self, a: &FaceVertex, b: &FaceVertex, c: &FaceVertex) -> f64 {
+        let v1 = self.vertices[a.vertex];
+        let v2 = self.vertices[b.vertex];
+        let v3 = self.vertices[c.vertex];
+        Vector3::area(v1, v2, v3)
+    }
+
     /// Returns the name of the current material, i.e. the material corresponding to the current
     /// part.
     pub fn current_material_name(&self) -> Option<String> {