Quadtree

本頁面說明 Maps SDK for iOS 公用程式庫提供的 Qudtree 公用程式。

四元樹是一種資料結構，可在搜尋點周圍的區域內搜尋，協助您尋找單一點附近的點。

使用二元樹可讓您有效搜尋 2D 範圍中的點，這些點都會定義為經緯度座標或購物車 (x, y) 座標。四角樹會將座標值區儲存在節點中，並按區域建立索引 (定界框)。如要尋找特定的座標組合，您可以周遊四棵樹的節點。

必要條件和注意事項

quadtree 公用程式包含在 Maps SDK for iOS 公用程式庫。如果您尚未設定程式庫，請先按照設定指南的步驟完成設定，再閱讀本頁面的其他內容。

加入方形樹並搜尋指定區域中的點

下列程式碼會建立四元樹，然後搜尋指定區域中的所有點：

import GoogleMapsUtils

class QuadTreeItem : NSObject, GQTPointQuadTreeItem {
  private let gqtPoint : GQTPoint

  init(point : GQTPoint) {
    self.gqtPoint = point
  }

  func point() -> GQTPoint {
    return gqtPoint
  }

  /// Function demonstrating how to create and use a quadtree
  private func test() {

    // Create a quadtree with bounds of [-2, -2] to [2, 2].
    let bounds = GQTBounds(minX: -2, minY: -2, maxX: 2, maxY: 2)
    guard let tree = GQTPointQuadTree(bounds: bounds) else {
      return
    }

    // Add 4 points to the tree.
    tree.add(QuadTreeItem(point: GQTPoint(x: -1, y: -1)))
    tree.add(QuadTreeItem(point: GQTPoint(x: -1, y: -1)))
    tree.add(QuadTreeItem(point: GQTPoint(x: -1, y: 1)))
    tree.add(QuadTreeItem(point: GQTPoint(x: 1, y: 1)))
    tree.add(QuadTreeItem(point: GQTPoint(x: 1, y: -1)))

    // Search for items within the rectangle with lower corner of (-1.5, -1.5)
    // and upper corner of (1.5, 1.5).
    let searchBounds = GQTBounds(minX: -1.5, minY: -1.5, maxX: 1.5, maxY: 1.5)
    for item in tree.search(with: searchBounds) as! [QuadTreeItem] {
      print("(\(item.point().x), \(item.point().y))");
    }
  }
}
      

@import GoogleMapsUtils;

@interface QuadTreeItem : NSObject<GQTPointQuadTreeItem>
- (instancetype)initWithPoint:(GQTPoint)point;
@end

@implementation QuadTreeItem {
  GQTPoint _point;
}

- (instancetype)initWithPoint:(GQTPoint)point {
  if ((self = [super init])) {
    _point = point;
  }
  return self;
}

- (GQTPoint)point {
  return _point;
}

/// Function demonstrating how to create and use a quadtree
- (void)test {
  // Create a quadtree with bounds of [-2, -2] to [2, 2].
  GQTBounds bounds = {-2, -2, 2, 2};
  GQTPointQuadTree *tree = [[GQTPointQuadTree alloc] initWithBounds:bounds];

  // Add 4 points to the tree.
  [tree add:[[QuadTreeItem alloc] initWithPoint:(GQTPoint){-1, -1}]];
  [tree add:[[QuadTreeItem alloc] initWithPoint:(GQTPoint){-1, 1}]];
  [tree add:[[QuadTreeItem alloc] initWithPoint:(GQTPoint){1, 1}]];
  [tree add:[[QuadTreeItem alloc] initWithPoint:(GQTPoint){1, -1}]];

  // Search for items within the rectangle with lower corner of (-1.5, -1.5)
  // and upper corner of (1.5, 1.5).
  NSArray *foundItems = [tree searchWithBounds:(GQTBounds){-1.5, -1.5, 1.5, 1.5}];

  for (QuadTreeItem *item in foundItems) {
    NSLog(@"(%lf, %lf)", item.point.x, item.point.y);
  }
}

@end