Finally, affordable high-precision GPS for drones

By Svetlana Emelyanova

Precision landings are becoming affordable for everyone, thanks to a new device that makes highly precise GPS affordable.

While drone users recognize the need for pinpoint GPS accuracy, most have settled for far less due to the prohibitive cost of more accurate systems. GPS receivers offering tolerances within centimeters can cost tens of thousands of dollars — well beyond the reach of most drone hobbyists and many prosumers. But now, low-cost solutions are beginning to emerge.

Reach, a high-precision GPS receiver from Emlid, based on the Intel® Edison microcomputer platform,  has been one of the most highly anticipated. When Emlid initially launched a crowdfunding campaign at Indiegogo to raise funds to manufacture the receiver, their target was just $27,000, but the campaign brought in $81,960 in preorders. The most popular order was for a set of two receivers, which can be used to enable precision landings. Drone pilots had spoken: at $235, with a weight of 12 g, measurements of 26 mm x 45 mm and the promise of highly-precise GPS, Reach fit their needs.

Reach makes high-precision GPS available in a small form factor suitable for drones and other applications. (Image: Emlid)

All about that base

Like existing professional devices, Reach uses Real-Time Kinematic algorithms and differential global positioning system technology to increase the precision of the measured position. The method uses the phase of the satellite signal’s carrier wave, rather than the information in the signal, because the carrier measurements have a lower margin of error. However, the challenge is to correctly align the signals and ensure that calculations are not off by one wave, or more waves, introducing inaccuracies in the calculated positions. RTK uses a base station at a known coordinate. The base station broadcasts its known location together with the code and carrier measurements for all the satellites in view, so the mobile clients can align the carrier wave phases correctly. This enables the mobile devices to calculate their position relative to the base station with a high degree of precision. Base stations can be temporary or permanent and many devices, up to 20km away, can use the same base station for their corrections. A Reach device can be used as a mobile client, or as a base station if it is stationary and its coordinates are known.

The position of base stations can be measured accurately using commercially or freely available correction services in many countries, including the Continuously Operating Reference Stations network. If the precise location of the base station is not known, the mobile clients can still consistently and accurately calculate their position relative to the base station. 

Positioning accuracy with the help of Reach. Red dots show normal GPS precision in good conditions. Green dots show positions provided by Reach in RTK mode. The receiver was kept stationary so in an ideal situation there would be no deviation. The graph shows that Reach provides positions with less deviation, because the green dots are much closer together. The numbered dots are the most recently plotted points in this real-time graph. Please note the scale. (Image: Emlid)


A look inside Reach

The Reach hardware platform consists of three components: an Intel Edison computer running a custom, Yocto-built, Linux operating system and RTKLIB; a U-blox GPS-receiver; and an external Tallysman antenna, which plays an important role in enabling accurate positioning. The antenna weighs approximately 20 g and measures approximately 30 mm x 30 mm, so it can be easily fitted to a drone.

The receiver supports the GPS satellite constellation of the US, as well as Russia’s Glonass, China’s Beidou and Japan’s QZSS. In the future, Emlid plans to add support for the EU’s Galileo satellite constellation to improve signal availability. Using more satellites enables Reach to improve the precision of the calculated coordinates and the solution availability.

In addition to the satellite receiver, Reach has a number of other sensors: a tri-axial gyroscope, an accelerometer and a magnetometer. In the future, the device software will be upgraded to enable it to use these sensors to extrapolate the position when the signal is blocked — by the device going through a tunnel, for example — and to measure the tilt or roll of the device.

Reach comes with the connectors needed to integrate with major autopilots on the market, and Emlid has recently released integrations with Pixhawk and its own Navio autopilot. The integration with the autopilot enables GPS data to be tunneled through the radio signal used for flight control and mission planning.

Precision landings: A video shows the precision of a drone landing using Reach. (Image: Emlid)

Managing Reach in the browser

The software for Reach is based on the RTKLIB toolkit developed by Tomoji Takasu and supported by the open source community (The toolkit has a BSD License). The ReachView software enables any device with a web browser to connect to Reach to set up RTKLIB, view device logs, assess the quality of satellite observations, change streaming settings, configure connections and check the device position.  

ReachView: Using the ReachView software, any device with a browser can be used to access a Reach device. (Image: Emlid)

Building on Intel Edison

Why did the developers select Edison? “The size and form factor were important, especially for drone applications,” said Igor Vereninov, co-founder at Emlid. “We were able to build a device that is not larger than the Intel Edison board itself. The best thing about Intel Edison is the price-performance ratio. It’s a really powerful platform, using x86 architecture, with wi-fi and Bluetooth integrated. Wi-fi is important for connecting to the Internet to receive corrections from the base station. When you’re trying to integrate radio frequency equipment, you usually need to certify it, but with Intel Edison everything is preintegrated and precertified.”

The Intel Edison platform has 4 GB memory to log data, so that it can be analyzed with greater precision after data collection. USB can be used to connect radios for communication between Reach devices and in the future 3G communications and flash drive logging could be added through software updates.

The device has a number of interfaces. UART can be used to integrate with autopilots, and GPIO pins can be used to control a camera or trigger another device. I2C is often used in drones to communicate to external devices and is also supported on Reach.

Reach can be powered through the USB port, powered from the autopilot in a drone, or powered using a power bank typically used for charging a mobile phone.

Published Wednesday, June 22nd, 2016

Written by Svetlana Emelyanova

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