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下面代碼展示如何計算上圖中箭頭的旋轉(zhuǎn)方向

- (void)updateRoute:(NSArray<LocalCoordinate *> *)route {
    //route 中放的是LocalCoordinate 它有x和y坐標值 兩個屬性
    //用于記錄上一個坐標
    LocalCoordinate *lcoordinate = [[LocalCoordinate allco] initwithX:0.0 y:0.0];
    NSInteger count = route.count;
    for (NSInteger i = 0; i < count; i++) {
        @autoreleasepool {
            //獲取當前坐標點
            LocalCoordinate *coordinate = route[i];
            //使用向量計算夾角
            CGFloat v_x = [coordinate x];
            CGFloat v_y = [coordinate y];
            if (lcoordinate) {
                v_x = [coordinate x]-[lcoordinate x];
                v_y = [coordinate y]-[lcoordinate y];
            }
            double angle = 0.0;
            double m = sqrt(pow(v_x, 2)+pow(v_y, 2));
            if (m != 0) {
                angle = v_x<0?-acos(v_y/m):acos(v_y/m);
            }
            //----------這段是計算當前箭頭的位置 不需要的話可以忽略----------
            double x_2 = 0.0;
            double y_2 = 0.0;
            x_2 = ([coordinate x]+[lcoordinate x])/2.0;
            y_2 = ([coordinate y]+[lcoordinate y])/2.0;
            SCNVector3 vector3 = SCNVector3Make(self.floor.worldTransform.m41+x_2, self.floor.worldTransform.m42+0.01, self.floor.worldTransform.m43+y_2);
            //----------這段是計算當前箭頭的位置 不需要的話可以忽略----------
            SCNNode *node = self.routeNodes[i];
            node.position = vector3;
            node.transform = SCNMatrix4Translate(node.transform, 0, 1.1, 0);
            //設(shè)置歐拉角
            node.eulerAngles = SCNVector3Make(0, angle, 0);
            lcoordinate = coordinate;
        }
    }
}