ARKit保存对象位置并在任何下一个会话中查看它 [英] ARKit save object position and see it in any next session

问题描述

我正在使用ARKit开展项目。我需要保存一个对象位置，我希望在我的下一个应用程序启动时看到它。例如，在我的办公室里，我在门上贴了一些文字然后回到家里，第二天我希望在ARKit上可以看到那个地方的文字。

I am working for a project using ARKit. I need to save an object position and I want to see it in my next application launch where ever it was. For example in my office I attached some text on a door and come back to home and next day I wish to see that text on that place where it was is it possible in ARKit.

推荐答案

在iOS 12中：是！

ARKit 2，又称为iOS 12的ARKit，添加了一组功能Apple称之为世界地图持久性和共享。您可以获取ARKit了解其本地环境的所有信息，包括您用于跟踪虚拟内容的真实位置的任何 ARAnchor ，并将其保存在 ARWorldMap 对象。

In iOS 12: Yes!

"ARKit 2", aka ARKit for iOS 12, adds a set of features Apple calls "world map persistence and sharing". You can take everything ARKit knows about its local environment, including any ARAnchors you're using to track the real-world positions of virtual content, and save it in an ARWorldMap object.

然后，您可以将该对象序列化为文件，并稍后加载该文件以有效地恢复先前的AR会话（如果用户位于同一本地环境中）。成功重新定位到世界地图后，您的会话在保存之前具有所有相同的 ARAnchor ，因此您可以使用它来重新创建虚拟内容（例如使用已保存/已恢复锚点的名称来决定要显示的3D模型。

Then you can serialize that object to a file, and load the file later to effectively resume the earlier AR session (if the user is in the same local environment). Upon successfully "relocalizing" to the world map, your session has all the same ARAnchors it did before saving, so you can use that to re-create your virtual content (e.g. use the name of a saved/restored anchor to decide which 3D model to show).

有关详细信息，请参阅 WWDC18关于ARKit 2的讨论或 Apple的ARKit文档和示例代码。

For more info, see the WWDC18 talk on ARKit 2 or Apple's ARKit docs and sample code.

在iOS 12之前，ARKit没有提供使其本地世界映射的任何结果持久化的方法。您在AR会话中执行的所有操作，每个点，都只在该会话的上下文中定义。如果您根据平面检测，点击测试和/或用户输入放置一些虚拟内容，则该位置的参考框架相对于您的设备在会话开始时的位置。

Before iOS 12, ARKit doesn’t provide a way to make any results of its local-world mapping persistent. Everything you do, every point you locate, within an AR session is defined only in the context of that session. If you place some virtual content based on plane detection, hit testing, and/or user input, the frame of reference for that position is relative to where your device was at the beginning of the session.

由于没有可以跨会话持续存在的参考框架，因此无法定位虚拟内容，使其在（完全）退出/重新启动应用程序后看起来保持在相同的真实位置/方向。

With no frame of reference that can persist across sessions, there’s no way to position virtual content that’ll have it appear to stay in the same real-world position/orientation after (fully) quitting/restarting the app.

iOS 11.3中ARKit 1.5的一个补充是排序此问题的逃生阀：图像检测。如果您的应用程序的用例涉及已知/受控环境（例如，使用虚拟叠加层来指导美术馆中的访问者），并且在该环境中存在一些易于识别的2D功能（如着名的绘画），ARKit可以检测其位置。

One of the additions from "ARKit 1.5" in iOS 11.3 is sort of an escape valve for this problem: image detection. If your app’s use case involves a known/controlled environment (for example, using virtual overlays to guide visitors in an art museum), and there are some easily recognizable 2D features in that environment (like notable paintings), ARKit can detect their positions.

一旦你检测到一个你知道环境的固定特征的图像锚点，就可以告诉你的AR会话重新定义围绕该锚点的世界坐标系统（请参阅 setWorldOrigin ）。在这样做之后，您实际上在多个会话中有一个相同的坐标系统（假设您检测到相同的图像并在每个会话中设置世界原点）。

Once you’ve detected an image anchor that you know is a fixed feature of the environment, you can tell your AR Session to redefine its world coordinate system around that anchor (see setWorldOrigin). After doing that, you effectively have a coordinate system that’s the same across multiple sessions (assuming you detect the same image and set the world origin in each session).

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