Added circle_intersect() calculation to maths.scad.

readme.md

@@ -5455,6 +5455,7 @@ Maths utilities for manipulating vectors and matrices.
 | ```argsinh(x)``` | inverse hyperbolic sine |
 | ```argtanh(x)``` | inverse hyperbolic tangent |
 | ```augment(m)``` | Augment a matrix by adding an identity matrix to the right |
+| ```circle_intersect(c1, r1, c2, r2)``` | Calculate one point where two circles in the X-Z plane intersect, clockwise around c1 |
 | ```cosh(x)``` | hyperbolic cosine |
 | ```coth(x)``` | hyperbolic cotangent |
 | ```degrees(radians)``` | Convert degrees to radians |

utils/maths.scad

@@ -146,3 +146,10 @@ function invert(m) = let(n =len(m), m = solve(augment(m))) [ //! Invert a matrix
              each m[i][j]
     ]
 ];
+
+function circle_intersect(c1, r1, c2, r2) =     //! Calculate one point where two circles in the X-Z plane intersect, clockwise around c1
+    let(
+        v = c1 - c2,                            // Line between centres
+        d = norm(v),                            // Distance between centres
+        a = atan2(v.z, v.x) - acos((sqr(d) + sqr(r2) - sqr(r1)) / (2 * d * r2)) // Cosine rule to find angle from c2
+     ) c2 + r2 * [cos(a), 0, sin(a)];           // Point on second circle