How measuring apps became a reality

With their margins for error, we look at how far we should trust our phones to take accurate measurements

Many smartphone apps these days claim to do the same job as a ruler and the tape measure. 

We think of tape measures and rulers as infallible, accepting the information that they give us and rarely questioning it. If we want to measure a garment, a piece of furniture or even an empty space, we turn to these traditional methods because we trust them to do the job.

As the author Nassim Taleb observed in his book Fooled By Randomness: "Unless you have confidence in the ruler's reliability, if you use a ruler to measure a table, you may also be using the table to measure the ruler." He presented this as a metaphor, but he was right on a practical level, too. Without trust, a measuring device is no use to anyone.

Many smartphone apps now claim to do the job of the ruler and the tape measure.

Want to know the width of a table? Just fire up the camera, click on the start and end points you wish to measure between and let algorithms do the rest, with the final measurement presented as a number superimposed onto the screen.

Understanding augmented reality

There’s only one problem. As these apps freely admit, they have margins of error. The biggest battle they face is to establish the trust we already have in the humble ruler. If they can’t, what purpose do they serve?

Some would say that it’s churlish to criticise. After all, these apps are very clever examples of augmented reality (AR), where sensors embedded within phones and tablets can deduce valuable information about the world around it.

“This is something I’ve played with ever since college,” says Chris Laan of Laan Labs, which develops AirMeasure, a popular measuring app for Android and iOS. “While you could use the accelerometer to measure distance, the accuracy of the sensors wasn’t good enough. But now, algorithms can combine the information from a phone’s camera with data from its accelerometer and a gyroscope, locating the phone within a three-dimensional space and tracking its movements in real time.”

Many of these advances were made last summer with the launch of Apple’s ARKit and Google’s ARCore, sets of tools provided to app developers to allow them to access AR features in the latest phones and tablets.

Within weeks, Laan Labs had produced a proof of concept video of AirMeasure that immediately caused a stir on YouTube. The reactions of “fake!” that appeared in the comments section demonstrated how people found it implausible that angles, depth and perspective could all be determined by a phone.

“We discovered through user testing that people didn’t really know what AR was,” says Laan. “They didn’t understand that the phone could understand the world around it. It was hard to present the idea to people that they were interacting with a virtual space.”

How does it work?

First tentative steps in AR measuring certainly feel a little unusual. The initial hurdle is to understand that measurements can be taken from a distance; we’re so accustomed to measuring things by pressing rulers and tapes to the surface of the object we’re measuring, and it requires a leap of faith to trust a phone to perceive spatial depth correctly. But other features within these apps can help us to adapt our brains to their capabilities.

You can add virtual furniture to a room, create floor plans, or place three-dimensional spirit levels in a space to help align shelves or hang pictures. (The instinctive impulse, however, is still to use an old fashioned spirit level to check that the digital one is correct. Some habits are hard to break.)

Neither Apple nor Google would have known how its AR tools would be used by developers and which apps would be embraced by the public, but measurement has turned out to be unexpectedly popular.

“When we put the first video out,” says Laan, “people were dismissing it, but they were wrong.” According to the mobile analytics firm Sensor Tower, measurement tools account for 7 per cent of the 1,000 or so AR apps available for iOS, and have been downloaded more than two million times.

What to expect for the future

Both Apple and Google have capitalised upon this interest in the past couple of weeks by announcing their own measurement apps called Measure and Google Measure respectively.

Measure will be revealed to the public with the launch of iOS12 in September, while Google Measure is already available for a whole range of phones, including the Google Pixel 2 and Samsung Galaxy S9.

What’s puzzling, according to Chris Laan, is that these apps have been launched while the question of accuracy still lingers over the genre.

“Initially we had a disclaimer on AirMeasure saying look, this is a tool for estimates,” he says. “We didn’t want people building houses using it! Accuracy is still an issue, and we were caught off guard by Apple’s announcement. We had it in our head that Apple wouldn’t produce anything of substandard quality. But its Measure app still has issues that we struggled with at first – issues that we think we’ve overcome.”

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The fact is that the sensors in the average smartphone currently have limited power, and the software has to work very hard to deduce how those phones are moving and tilting.

That’s where errors creep in, and where trust in the technology breaks down. But those errors are getting ever-smaller over time.

The TrueDepth camera in the iPhone X, which has infrared depth detection, steps up the accuracy of measurement considerably, according to Laan. “In a year or two, all phones will start to have this technology,” he says, “and it’s only a matter of time before these measurements are 100 per cent accurate. It won’t even be a question any more.”

So, for the time being, it might be worth sticking with the old-fashioned methods of measurement that people have used since Biblical times. But by the end of the decade, measuring the length of objects by using notches on a stick is going to start feeling very old hat indeed.