Spritekit地面不接触屏幕底部

我正在制作一款spritekit游戏,一切正常,但我的场地在模拟器屏幕的中间。我尽了一切努力让它出现在屏幕的底部。一个功能。

let groundTexture = SKTexture(imageNamed: "Ground")
groundTexture.filteringMode = .nearest

for i in stride(from: 0, to: 2 + self.frame.size.width / groundTexture.size().width, by: 1) {

    let ground = SKSpriteNode(texture: groundTexture)
    ground.zPosition = 1.0 //-10
    //ground.position = CGPoint(x: (groundTexture.size().width / 2.0 + (groundTexture.size().width * CGFloat(i))), y: groundTexture.size().height / 4.0) //original position 

    ground.position = CGPoint(x: 0, y: groundTexture.size().height / +0)  //tried this from a tutorial 
    ground.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: self.frame.size.width * 2.0, height: groundTexture.size().height / 4.0)) //erase  * 4 test
    ground.setScale(1.2)
    ground.physicsBody?.isDynamic = false
    ground.physicsBody?.allowsRotation  = false
    ground.physicsBody?.affectedByGravity = false
    ground.physicsBody?.categoryBitMask = groundCategory 

    //contact and collision bitmask 
    ground.physicsBody?.contactTestBitMask = playerCategory | enemy1Category | enemy2Category | enemy3Category | enemy4Category | obstacleCategory | coinCatergory
    ground.physicsBody?.collisionBitMask = playerCategory | enemy1Category | enemy2Category | enemy3Category | enemy4Category | obstacleCategory | coinCatergory
    ground.physicsBody?.restitution = 0.0
    self.addChild(ground)

    let moveLeft = SKAction.moveBy(x: -groundTexture.size().width, y: 0, duration: 5)
    let moveReset = SKAction.moveBy(x: groundTexture.size().width, y: 0, duration: 0)
    let moveLoop = SKAction.sequence([moveLeft, moveReset])
    let moveForever = SKAction.repeatForever(moveLoop)

    ground.run(moveForever)
}