内容来源：https://blog.google/products-and-platforms/devices/pixel/pixel-watch-5-gps/

内容总结：

谷歌 Pixel Watch 5 于近日正式发布，其主打卖点之一便是号称“迄今最精准”的 GPS 路线追踪功能。据官方团队介绍，该手表在户外运动场景下的定位精度已超越苹果 Apple Watch Ultra 3 和佳明 Fenix 8 Pro。

为了实现这一突破，谷歌的工程师团队采取了一套“软硬结合”的组合方案。一方面，他们利用谷歌地图积累的全球建筑物三维模型数据，配合 AI 算法，有效消除了城市峡谷中 GPS 信号反射造成的定位偏移；另一方面，团队调用了谷歌在全球部署的 GPS 参考站网络，实时修正大气层干扰和卫星自身误差。

不过，将这套高精度方案塞进小小的手表里并非易事。工程师坦言，手表天线小、电池容量有限是两大硬件瓶颈。为此，他们创新性地采用了“数据压缩+云端处理”模式：手表只负责采集原始 GPS 数据并压缩上传，由服务器完成复杂的纠偏计算后再回传至 Google Health 应用，从而在保持精度提升的同时，不影响手表本身的续航表现。

在实测验证阶段，团队派出测试人员佩戴多种设备，在开阔地、林荫道和城市街区等不同环境下步行、跑步和骑行数千英里。测试结果显示，Pixel Watch 5 记录的轨迹与实际路线高度吻合，甚至一度让工程师怀疑是否误用了对照组数据。

据悉，Pixel Watch 5 已从 8 月 12 日起接受预订，并将于 8 月 20 日正式开售，起售价为 399 美元（41 毫米版）和 429 美元（45 毫米版）。

中文翻译：

我们如何打造Pixel Watch 5上的全新GPS

新款Pixel Watch 5提供了我们迄今为止最精准的GPS路线追踪功能。1 2 “任何智能手表的支柱之一都是健身功能，”Pixel Watch首席工程师沙拉斯·阿纳特表示，“而在健身领域，拥有精准的GPS路线至关重要。”

当你佩戴智能手表时，你希望能准确看到自己在户外锻炼期间经过的路线。也许你还想重温一次跑步、徒步或骑行的经历——回忆那段让你精疲力竭的山坡，或是那一见难忘的壮丽瀑布。“如果你的定位飘忽不定，就会破坏整个体验，”精准定位团队杰出工程师弗兰克·范迪格伦说道。

两人与各自团队携手合作，开发出了这款拥有我们迄今最精准GPS路线追踪功能的手表——性能超越Apple Watch Ultra 3和Garmin Fenix 8 Pro。3

当然，走到这一步付出了大量努力。以下是这段历程的幕后故事。

解决常见GPS问题

为了确定你所在的位置，GPS会测量卫星无线电信号到达设备所需的时间——然后乘以光速。接着，它会结合来自几颗不同卫星的测量数据来精确定位。但许多因素——比如大气条件、附近建筑物和卫星误差——都可能使这一计算出现偏差。

弗兰克的团队此前已经为其他Alphabet产品开发过解决方案，他们将那些方案进行了调整适配，用于Pixel Watch 5。

借助Google Maps，他们拥有了全球建筑物的三维模型。团队将该数据与AI结合，以减少GPS信号被建筑物反射所造成的误差。“你需要知道所有建筑物的位置，”弗兰克说，“但你也需要真正优秀的AI来做到位。”

在城市环境中，GPS信号会因建筑物反射而失真，使设备更难判断你所处的位置。

团队还利用了谷歌遍布全球的现有GPS参考站网络。这些站点测量GPS信号、核算偏差，并实时将这些数据提供给谷歌产品。这帮助他们减少了由大气条件和卫星误差带来的不准确性。

“我们将之前开发的方案与新技术相结合，取得了非常好的成果，”精准定位团队软件工程师伊马德·法图什表示。

将解决方案融入智能手表

解决这些常见的GPS误差仅仅是第一步——按照沙拉斯的估算，大约只占全部工作的三分之一。更大的挑战在于将该解决方案融入智能手表。

在智能手表中实现GPS功能颇具挑战性，原因有几个。首先，智能手表的天线很小，这就难以从GPS所依赖的卫星获取强信号。“硬件本身就限制了你的可能性，”Pixel Watch团队软件工程师马克·惠特利解释道。

电池续航也是一个问题。由于智能手表体积小，电池容量也小。而精准的GPS路线追踪需要大量数据——尤其是当你需要弥补智能手表小天线的不足时。

团队需要一种能够处理大量数据又不牺牲手表电池续航的方法。他们的解决方案是：压缩手表的原始GPS数据，发送到服务器进行处理和修正，再传输到Google Health应用的后端。（顺便说明一下，Pixel Watch 5的电池续航并未因这一改动而受到负面影响。）4

实地测试全新GPS

团队有了解决方案，但他们需要确保它在全球范围内都能正常工作——在开阔地带、树荫之下以及城市环境中。于是他们派出测试人员，佩戴多达四种不同类型的智能手表，还背着一个装有巨型天线的专用背包。

“我们派人去了不同的城市，”沙拉什说，“也派他们去了不同的国家。”测试人员步行、跑步和骑行累计达数千英里。

他们的测试结果几乎令人难以置信。“伊马德给我看了结果，”马克说，“我当时就想，‘你确定没有泄露真实轨迹数据吗？’”真实轨迹是团队的对照数据——本质上就是测试人员实际行走的路线。Pixel Watch 5的路线与真实轨迹路线高度吻合，以至于马克担心是某个故障导致显示了错误的数据。但事实并非如此。

“我们正在构建的那个解决方案？它真的奏效了，”弗兰克说。

以下是团队GPS路线追踪测试的部分结果。Pixel Watch 4的路线为红色，Pixel Watch 5的路线为蓝色，真实轨迹路线为绿色。

Pixel Watch 5将于8月12日起开启预售，8月20日正式上架，起售价为399美元（41毫米）和429美元（45毫米）。

英文来源：

How we built the new GPS on Pixel Watch 5
The new Pixel Watch 5 offers our most accurate GPS route tracking yet. 1 2 “One of the pillars of any smartwatch is fitness,” says Sharath Ananth, a lead engineer on Pixel Watch. “And in fitness, having accurate GPS routes is important.”
When you’re wearing a smartwatch, you want to be able to see exactly where you’ve been during outdoor workouts. Maybe you even want to relive a run, hike, or bike ride you took — remembering that killer hill you climbed or breathtaking waterfall you saw. “If your position is jumpy, it undermines the whole experience,” says Frank van Diggelen, a distinguished engineer on the Precision Location team.
The two worked together, alongside their teams, to develop a watch that has our most accurate GPS route tracking yet — outperforming the Apple Watch Ultra 3 and Garmin Fenix 8 Pro. 3
Naturally, getting there took a lot of work. Here’s a behind-the-scenes look at that journey.
Fixing common GPS problems
To figure out where you are, GPS measures how long it takes a satellite radio signal to reach your device — and multiplies that by the speed of light. It then combines measurements from a few different satellites to pinpoint your location. But lots of things — like atmospheric conditions, nearby buildings, and satellite errors — can throw that calculation off.
Frank’s team had already worked on fixes for other Alphabet products, and they modified those solutions for the Pixel Watch 5.
Thanks to Google Maps, they had three-dimensional models of buildings around the world. And the team paired that data with AI to cut down on errors caused by the GPS signal bouncing off buildings. “You need to know where all the buildings are,” Frank says. “But you also need really good AI to do it right.”
In urban settings, GPS signals can reflect off buildings, making it harder for your device to understand where you are.
The team also tapped Google’s existing network of GPS reference stations across the globe. These stations measure GPS signals, account for discrepancies, and serve that data to Google products in real time. This helped them cut down on inaccuracies from atmospheric conditions and satellite errors.
“We achieved very nice results by combining fixes we’d developed before with new technology,” says Imad Fattouch, a software engineer on the Precision Location team.
Fitting the solution into a smartwatch
Solving these common GPS errors was only the first step — roughly a third of the work, in Sharath’s estimation. The bigger challenge was fitting that solution into a smartwatch.
It’s challenging to build GPS capabilities into a smartwatch for a few reasons. For one thing, smartwatches have small antennas. That makes it hard to get a strong signal from the satellites GPS relies on. “The hardware just limits you,” explains Mark Wheatley, a software engineer on the Pixel Watch team.
Battery life is also a problem. Since smartwatches are small, they have small batteries. And accurate GPS route tracking requires a lot of data — especially when you’re compensating for a smartwatch’s small antenna.
The team needed a way to handle lots of data without sacrificing the watch’s battery life. Their solution? Compressing the watch’s raw GPS data, sending it to a server to get processed and corrected, and delivering it to the Google Health app back-end. (And for the record, the Pixel Watch 5’s battery life wasn’t negatively affected by this change.) 4
Putting the new GPS to the test
The team had their solution, but they needed to ensure it worked across the world — in open air, under tree cover, and in urban environments. So they sent testers out wearing up to four different types of smartwatches and a special backpack equipped with a massive antenna.
“We’ve sent people to different cities,” Sharath says. “We’ve sent them to different countries.” The testers walked, ran, and biked thousands of miles.
Their findings were almost unbelievable. “Imad showed me the results,” Mark says. “And I was like, ‘Are you sure you haven’t leaked ground truth?’” Ground truth is the team’s control data — essentially, the route the tester actually took. The Pixel Watch 5 route was similar enough to the ground truth route that Mark worried a glitch had caused the wrong data to show up. It hadn’t.
“That solution we were building? It worked,” says Frank.
Here are some results from the team's GPS route tracking tests. Pixel Watch 4's route is red, Pixel Watch 5's route is blue, and the ground truth route is green.
Pixel Watch 5 is available for preorder starting August 12 and will be on shelves August 20, starting at $399 (41mm) and $429 (45mm).