code: function(aabb1,aabb2){
          this.minX = (aabb1.minX<aabb2.minX) ? aabb1.minX : aabb2.minX;
          this.maxX = (aabb1.maxX>aabb2.maxX) ? aabb1.maxX : aabb2.maxX;
          this.minY = (aabb1.minY<aabb2.minY) ? aabb1.minY : aabb2.minY;
          this.maxY = (aabb1.maxY>aabb2.maxY) ? aabb1.maxY : aabb2.maxY;
          this.minZ = (aabb1.minZ<aabb2.minZ) ? aabb1.minZ : aabb2.minZ;
          this.maxZ = (aabb1.maxZ>aabb2.maxZ) ? aabb1.maxZ : aabb2.maxZ;
          /*
          var margin=0;
          this.minX-=margin;
          this.minY-=margin;
          this.minZ-=margin;
          this.maxX+=margin;
          this.maxY+=margin;
          this.maxZ+=margin;
          */
      }
docs: Set this AABB to the combined AABB of aabb1 and aabb2.
  @param   aabb1
  @param   aabb2