diff --git a/src/geo/polygon.js b/src/geo/polygon.js
index 71427ff6..c8414b63 100644
--- a/src/geo/polygon.js
+++ b/src/geo/polygon.js
@@ -1757,6 +1757,10 @@
         return (a1 > a2) ? a2 / a1 : a1 / a2;
     };
 
+    PRO.areaOrLength = function(poly) {
+        return this.length === poly.length || this.areaDiff(poly) > 0.98;
+    };
+
     /**
      * return logical OR of two polygons' enclosed areas
      *
@@ -1765,7 +1769,65 @@
      */
     PRO.union = function(poly, min, all) {
         if (!this.overlaps(poly)) return null;
-        return POLY.union([this,poly], min, all);
+
+        let fillang = this.fillang && this.area() > poly.area() ? this.fillang : poly.fillang,
+            clib = self.ClipperLib,
+            ctyp = clib.ClipType,
+            ptyp = clib.PolyType,
+            cfil = clib.PolyFillType,
+            clip = new clib.Clipper(),
+            ctre = new clib.PolyTree(),
+            sp1 = this.toClipper(),
+            sp2 = poly.toClipper(),
+            minarea = min >= 0 ? min : 0.1;
+
+        clip.AddPaths(sp1, ptyp.ptSubject, true);
+        clip.AddPaths(sp2, ptyp.ptClip, true);
+
+        if (clip.Execute(ctyp.ctUnion, ctre, cfil.pftEvenOdd, cfil.pftEvenOdd)) {
+            let union = POLY().fromClipperTreeUnion(ctre, poly.getZ(), minarea);
+            if (all) {
+                if (union.length === 2) {
+                    let src = [ this.leftmost(), poly.leftmost() ];
+                    let dst = [ union[0].leftmost(), union[1].leftmost() ];
+
+                    if (leftmost(src[0], src[1]) === src[1]) {
+                        src.reverse();
+                    }
+                    if (leftmost(dst[0], dst[1]) === dst[1]) {
+                        dst.reverse();
+                    }
+                    if (
+                        src[0].poly && src[1].poly && // missing for cam tabs
+                        src[0].isEqual2D(dst[0]) &&
+                        src[1].isEqual2D(dst[1]) &&
+                        src[0].poly.areaOrLength(dst[0].poly) &&
+                        src[1].poly.areaOrLength(dst[1].poly)
+                    ) {
+                        return null;
+                    // } else {
+                    //     console.log("union debug", {
+                    //         src,
+                    //         dst,
+                    //         d0: src[0].poly.areaDiff(dst[0].poly),
+                    //         d1: src[1].poly.areaDiff(dst[1].poly),
+                    //         m0: src[0].isEqual2D(dst[0]),
+                    //         m1: src[1].isEqual2D(dst[1])
+                    //     });
+                    }
+                }
+                return union;
+            }
+            if (union.length === 1) {
+                union = union[0];
+                union.fillang = fillang;
+                return union;
+            } else {
+                console.trace({check_union_call_path: union, this: this, poly});
+            }
+        }
+
+        return null;
      };
 
     /** ******************************************************************
diff --git a/src/geo/polygons.js b/src/geo/polygons.js
index 8315b866..8136a0ff 100644
--- a/src/geo/polygons.js
+++ b/src/geo/polygons.js
@@ -392,19 +392,31 @@
              }
          }
 
-         let clib = self.ClipperLib,
-             ctyp = clib.ClipType,
-             ptyp = clib.PolyType,
-             clip = new clib.Clipper(),
-             ctre = new clib.PolyTree();
+         let out = polys.slice(), i, j, union, uset = [];
 
-         clip.AddPaths(toClipper(polys), ptyp.ptSubject, true);
-
-         if (clip.Execute(ctyp.ctUnion, ctre)) {
-             return fromClipperTree(ctre, polys[0].getZ());
-         } else {
-             return [];
+         outer: for (i=0; i<out.length; i++) {
+             if (!out[i]) continue;
+             for (j=i+1; j<out.length; j++) {
+                 if (!out[j]) continue;
+                 union = out[i].union(out[j], minarea, all);
+                 if (union) {
+                     out[i] = null;
+                     out[j] = null;
+                     if (all) {
+                         out.appendAll(union);
+                     } else {
+                         out.push(union);
+                     }
+                     continue outer;
+                 }
+             }
          }
+
+         for (i=0; i<out.length; i++) {
+             if (out[i]) uset.push(out[i]);
+         }
+
+         return uset;
      }
 
     /**