fix determinant

src/geo/base.js

@@ -323,7 +323,7 @@
     {
         let denominator = 2*determinant33([[A.x, A.y, 1], [B.x, B.y, 1], [C.x, C.y, 1]]);
         let xmat = [[A.x*A.x + A.y*A.y, A.y, 1],[B.x*B.x + B.y*B.y, B.y, 1],[C.x*C.x + C.y*C.y, C.y, 1]];
-        let ymat = [[A.y, A.x*A.x + A.y*A.y, 1],[B.y, B.x*B.x + B.y*B.y, 1],[C.y, C.x*C.x + C.y*C.y, 1]];
+        let ymat = [[A.x, A.x*A.x + A.y*A.y, 1],[B.x, B.x*B.x + B.y*B.y, 1],[C.x, C.x*C.x + C.y*C.y, 1]];
 
         let center = {x:determinant33(xmat)/denominator, y:determinant33(ymat)/denominator, z:A.z};
 
@@ -358,8 +358,6 @@
         return center;
     }
 
-
-
     /**
      * return two possible circle centers given two points and a radius
      * https://stackoverflow.com/questions/36211171/finding-center-of-a-circle-given-two-points-and-radius