Added Triangle.Area, Triangle.CircumCenter and Triangle.CircumCircle methods, as they're all really useful when dealing with Triangles.

v3/src/checksum.js

@@ -1,4 +1,4 @@
 var CHECKSUM = {
-build: 'a69a1650-14e2-11e7-b8c3-bdb77b9e9c3e'
+build: '36a75180-14e9-11e7-ba0a-191be9c0e55a'
 };
 module.exports = CHECKSUM;

v3/src/geom/triangle/Area.js

@@ -0,0 +1,17 @@
+// The 2D area of a triangle. The area value is always non-negative.
+
+var Area = function (triangle)
+{
+    var x1 = triangle.x1;
+    var y1 = triangle.y1;
+
+    var x2 = triangle.x2;
+    var y2 = triangle.y2;
+
+    var x3 = triangle.x3;
+    var y3 = triangle.y3;
+
+    return Math.abs(((x3 - x1) * (y2 - y1) - (x2 - x1) * (y3 - y1)) / 2);
+};
+
+module.exports = Area;

v3/src/geom/triangle/CircumCenter.js

@@ -0,0 +1,56 @@
+//  Adapted from http://bjornharrtell.github.io/jsts/doc/api/jsts_geom_Triangle.js.html
+
+/**
+ * Computes the determinant of a 2x2 matrix. Uses standard double-precision
+ * arithmetic, so is susceptible to round-off error.
+ *
+ * @param {Number}
+ *          m00 the [0,0] entry of the matrix.
+ * @param {Number}
+ *          m01 the [0,1] entry of the matrix.
+ * @param {Number}
+ *          m10 the [1,0] entry of the matrix.
+ * @param {Number}
+ *          m11 the [1,1] entry of the matrix.
+ * @return {Number} the determinant.
+ */
+function det (m00, m01, m10, m11)
+{
+    return (m00 * m11) - (m01 * m10);
+}
+
+/**
+ * Computes the circumcentre of a triangle. The circumcentre is the centre of
+ * the circumcircle, the smallest circle which encloses the triangle. It is also
+ * the common intersection point of the perpendicular bisectors of the sides of
+ * the triangle, and is the only point which has equal distance to all three
+ * vertices of the triangle.
+ * <p>
+ * This method uses an algorithm due to J.R.Shewchuk which uses normalization to
+ * the origin to improve the accuracy of computation. (See <i>Lecture Notes on
+ * Geometric Robustness</i>, Jonathan Richard Shewchuk, 1999).
+ */
+var CircumCenter = function (triangle, out)
+{
+    if (out === undefined) { out = { x: 0, y: 0 }; }
+
+    var cx = triangle.x3;
+    var cy = triangle.y3;
+
+    var ax = triangle.x1 - cx;
+    var ay = triangle.y1 - cy;
+
+    var bx = triangle.x2 - cx;
+    var by = triangle.y2 - cy;
+
+    var denom = 2 * det(ax, ay, bx, by);
+    var numx = det(ay, ax * ax + ay * ay, by, bx * bx + by * by);
+    var numy = det(ax, ax * ax + ay * ay, bx, bx * bx + by * by);
+
+    out.x = cx - numx / denom;
+    out.y = cy + numy / denom;
+
+    return out;
+};
+
+module.exports = CircumCenter;

v3/src/geom/triangle/CircumCircle.js

@@ -0,0 +1,56 @@
+//  Adapted from https://gist.github.com/mutoo/5617691
+
+var CircumCircle = function (triangle, out)
+{
+    if (out === undefined) { out = { x: 0, y: 0, radius: 0 }; }
+
+    //  A
+    var x1 = triangle.x1;
+    var y1 = triangle.y1;
+
+    //  B
+    var x2 = triangle.x2;
+    var y2 = triangle.y2;
+
+    //  C
+    var x3 = triangle.x3;
+    var y3 = triangle.y3;
+
+    var A = x2 - x1;
+    var B = y2 - y1;
+    var C = x3 - x1;
+    var D = y3 - y1;
+    var E = A * (x1 + x2) + B * (y1 + y2);
+    var F = C * (x1 + x3) + D * (y1 + y3);
+    var G = 2 * (A * (y3 - y2) - B * (x3 - x2));
+
+    var dx;
+    var dy;
+
+    //  If the points of the triangle are collinear, then just find the
+    //  extremes and use the midpoint as the center of the circumcircle.
+
+    if (Math.abs(G) < 0.000001)
+    {
+        var minX = Math.min(x1, x2, x3);
+        var minY = Math.min(y1, y2, y3);
+        dx = (Math.max(x1, x2, x3) - minX) * 0.5;
+        dy = (Math.max(y1, y2, y3) - minY) * 0.5;
+
+        out.x = minX + dx;
+        out.y = minY + dy;
+        out.radius = Math.sqrt(dx * dx + dy * dy);
+    }
+    else
+    {
+        out.x = (D * E - B * F) / G;
+        out.y = (A * F - C * E) / G;
+        dx = out.x - x1;
+        dy = out.y - y1;
+        out.radius = Math.sqrt(dx * dx + dy * dy);
+    }
+
+    return out;
+};
+
+module.exports = CircumCircle;

v3/src/geom/triangle/index.js

@@ -3,6 +3,8 @@
 var Triangle = require('./Triangle');
 
 Triangle.Centroid = require('./Centroid');
+Triangle.CircumCenter = require('./CircumCenter');
+Triangle.CircumCircle = require('./CircumCircle');
 Triangle.Contains = require('./Contains');
 Triangle.ContainsPoint = require('./ContainsPoint');
 Triangle.InCenter = require('./InCenter');