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Low-cost RTK GPS receiver (centimeter level precision) with open source software and board design targeted at UAVs.
Low-cost RTK GPS receiver (centimeter level precision) with open source software and board design targeted at UAVs.
303 backers pledged $166,097 to help bring this project to life.

About this project

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Update - New Reward: Rugged Piksi with Bluetooth

We’ve had a lot of interest in the Piksi RTK system from professionals in the GIS and mapping fields, but our RTK Kit alone was not enough to fulfill this need. To use Piksi in these settings, you need a durable, integrated solution - one that can be turned on with the flick of a switch, and is accompanied by an easy, intuitive user interface.

So, we have added a new reward, a ruggedized version of our RTK Kit containing two Piksi receivers each fully assembled with an enclosure, a Bluetooth module, an SD card slot, an integrated radio link, and 10 hours of rechargeable Lithium Polymer batteries.

We’ll also be releasing data collection apps for Android and iOS that interface with Piksi over Bluetooth; you’ll be able to take measurements, plot points on your smartphone’s map, and for professionals, export to common formats to integrate into your standard mapping workflow - all with the 4 centimeter accuracy of the Piksi RTK system.

The ruggedized version of Piksi will also serve as an integrated reference station for UAV users. This will eliminate the need to connect the reference station Piksi to an external power source or radio link, and give it protection from dirt, moisture, and the external environment. It will also allow add on-board logging capability and the ability to communicate with the user’s Android or iOS device.

See the Rewards section for details on the new Ruggedized RTK Kit reward.

What is RTK?

A regular GPS receiver, like you have in your cell phone, gives positions that are accurate to within a few meters. An RTK (Real Time Kinematic) GPS system gives positions that are 100 times more accurate - down to single centimeters.

What is Piksi?

Piksi is an RTK GPS receiver with open source software that costs one tenth [1] the price of any other available RTK system.

We designed Piksi with the belief that providing this level of positioning precision at a radically lower cost would open it up to a much wider range of applications. We are particularly excited about its use in autonomous vehicle systems. Civilian and hobbyist use of UAVs has increased dramatically over the last few years, yet highly accurate, low cost localization solutions are not available yet. We hope that Piksi will help to fill this gap and push the envelope of what is possible with these systems.

Some possible applications:

  • UAVs
  • Amateur rocketry
  • Autonomous cars
  • Construction measurements
  • Surveying
  • Heading and attitude determination
  • GPS education
  • Reception of new constellations (Galileo, GLONASS, Compass, etc.)
  • Geo-referencing of aerial photography
  • Autonomous lawnmowers

Piksi Technical Specs:

  • Centimeter level positioning (RTK)
  • Fast (50 Hz) position/velocity/time updates
  • Open source software and board design
  • Low power consumption : 500mW / 100mA typical
  • Small form factor : 53 x 53 mm
  • Low cost : $900 for a complete RTK system

For full technical specifications, check out the Piksi datasheet. User guides, code documentation, software and hardware repositories, and CAD models are all available on the Documentation Wiki.

A flexible platform

From the start, we wanted Piksi to be an indispensable tool for GPS experimentation. Whether you want to test out a new algorithm, receive signals from new constellations, more closely integrate and tune your receiver for your application, or teach yourself about GPS, Piksi gives you the flexibility, power, and transparency to do it.

PCB Layout and Schematics are available in Eagle format.
PCB Layout and Schematics are available in Eagle format.

The software that runs on Piksi is open source, as are the PCB schematics and layout. The development toolchain is supported on Linux, Windows, and OSX.

Screenshot of Peregrine - Swift Navigation's GPS post-processing software.
Screenshot of Peregrine - Swift Navigation's GPS post-processing software.

We’ve also developed an open source GPS post-processing tool, Peregrine, that provides a high-level interface to the same open source GPS library as used by the Piksi firmware. Raw GPS samples can be passed through Piksi over USB to a PC and post-processed with Peregrine. Being written in Python, Peregrine is well-suited for rapid development of new algorithms that can then be quickly transitioned to running standalone on the Piksi hardware.

How does RTK work?

GPS receiver measuring the distances to four satellites: the minimum number for a position fix.
GPS receiver measuring the distances to four satellites: the minimum number for a position fix.

A GPS receiver determines its position by measuring its distance to four or more GPS satellites. By comparing the relative phase offsets of unique 'codes' continually transmitted by the satellites, the receiver can determine the relative distance to each satellite. Each bit of the codes is about 300 meters in length, which in practice limits the precision to which the receiver can measure the code phase to a few meters. This is one reason that a normal receiver cannot achieve centimeter level accuracy.

The ionosphere slows GPS signals, a source of error that RTK systems mitigate.
The ionosphere slows GPS signals, a source of error that RTK systems mitigate.

Another important source of error for GPS receivers is ionospheric delay. When GPS signals travel through the ionosphere, they are slowed, adding a few meters of error to the distance measurement. The amount the signal is slowed varies over time and location, and is difficult to predict.

An RTK GPS receiver achieves centimeter level accuracy by mitigating these two sources of error. 

RTK receivers measure the phase of the carrier wave (bottom) for greater precision.
RTK receivers measure the phase of the carrier wave (bottom) for greater precision.

First, in addition to measuring the code phase, an RTK GPS receiver measures the phase of the carrier wave that the code is modulated upon. The carrier has a wavelength of about 19 centimeters. This makes it possible to measure to a much greater degree of accuracy than the 300 meter code, but there is a catch - there are an unknown number of whole carrier wavelengths between the satellite and receiver. Clever algorithms are required to resolve this "integer ambiguity" by checking that the code and carrier phase measurements lead to a consistent position solution as the satellites move and the geometry of the problem changes.

Cancellation of the common ionospheric error allows computation of the relative receiver position to a high degree of accuracy.
Cancellation of the common ionospheric error allows computation of the relative receiver position to a high degree of accuracy.

Second, an RTK GPS receiver is able to reduce the ionospheric error with the help of an additional reference receiver. The ionospheric delay varies only slowly with location, so with a nearby reference receiver, the delay is almost the same for both receivers and can largely be cancelled out. This is why an RTK GPS system uses two receivers.

Project status

Our GUI console showing position solutions in real time.
Our GUI console showing position solutions in real time.

We currently have 25 pre-production Piksi receivers (identical to the production ones) assembled and ready to ship. The Piksi firmware currently supports the functionality of a normal GPS receiver, without RTK, and we've started the implementing the RTK functionality. We've also written a host of PC-side development tools to make it easy to interact with the hardware. The development toolchain is supported on Linux, Windows, and OSX.

We’ll use the Kickstarter funding to pay for development costs that we incur while finishing the RTK functionality. We’ll also be refining the development tools and adding more documentation to make using Piksi a delight for developers and end users of any background.

Estimated Schedule

Our estimated production and delivery timeline.
Our estimated production and delivery timeline.

Please note that whilst these are our best estimates, as with all development projects there is always going to be some uncertainty in delivery dates and the possibility for unforeseen problems and delays.

Rewards

We are offering two main rewards, the PIKSI and the RTK KIT. The PIKSI is simply a single Piksi receiver for people who only need one receiver. As we explained in our technical section above you need two receivers to do RTK so the PIKSI reward on its own won't allow you to get centimeter level precision.

The RTK KIT reward is the main deal. It contains two Piksi receivers and everything else you need to do centimeter level RTK positioning. Have a look at this diagram which shows how it all fits together:

Diagram of the Piksi RTK System : One Piksi on the ground as a reference receiver, sending ranging corrections to a Piksi onboard a UAV.
Diagram of the Piksi RTK System : One Piksi on the ground as a reference receiver, sending ranging corrections to a Piksi onboard a UAV.

We are offering two versions of our PIKSI and RTK KIT rewards. The Developer Edition and the Production Edition. These two versions both contain identical hardware.

The difference is that the Developer Edition rewards will be shipped from the small batch of Piksi receivers that we already have assembled and will ship immediately after the Kickstarter campaign ends. Please be aware that Developer Edition rewards will ship before the RTK software development is complete.

We will be starting a new full production run of hardware for the Production Edition rewards which will be ready to ship in December when the RTK software development is complete.

PIKSI rewards include: 

  • 1 Piksi
  • 1 Swift Navigation retractable Micro-USB cable
  • 2 cable assemblies for connecting devices to Piksi’s UART headers

RTK KIT rewards include

  • 2 Piksi receivers
  • 2 Swift Navigation retractable Micro-USB cables
  • 4 cable assemblies for connecting devices to the Piksi UART headers
  • 2 XBee radios
  • 2 cable assemblies for connecting the XBee radios to the Piksi receivers

Ruggedized RTK KIT rewards include 2 Ruggedized Piksi receivers, each made up of:

  • Piksi
  • Ruggedized plastic case
  • Radio link and antenna
  • Bluetooth transceiver
  • SD Card Slot
  • Re-chargable Lithium Polymer batteries

Who are Swift Navigation?

The Swift Navigation team: Colin Beighley and Fergus Noble
The Swift Navigation team: Colin Beighley and Fergus Noble

We previously worked at a company named Joby Energy where we successfully developed an RTK GPS system for high-altitude wind turbines. This system was used to guide UAV’s in highly dynamic environments (greater than 8g accelerations, over 100mph). We've both been working on GPS full time for the past 2-3 years, and were working on our own independent GPS projects before that. See our Kickstarter bio for more information. And for those interested, here’s a presentation we gave at Defcon 2012 on GPS.

Risks and challenges

We have already built a small batch of Piksi receivers that are ready to ship and have locked down all part sourcing and manufacturing for further batches, so there are unlikely to be any unanticipated delays in the delivery of Piksi hardware.

However, it’s difficult to know exactly how long the RTK functionality will take to implement - software development schedules seem to always run over their anticipated delivery dates, even when you take into account Hofstadter's Law. We feel the goals we’re proposing to accomplish with this campaign are reasonable - adding a new set of software functionality (which we successfully implemented on a previous platform) upon an existing base of stable hardware and software.

We’ve planned out the development schedule with these facts in mind, giving ourselves enough time to have the new features finished by the delivery date.

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  1. Select this reward

    Pledge $7 or more About $7

    SUPPORTER: You'll receive our sincere thanks and a snazzy Swift Navigation retractable Micro-USB cable as a token of our gratitude.

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    T-SHIRT: You'll be the envy of your friends and co-workers sporting this fine T-Shirt emblazoned with the Swift Navigation logo.

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    Pledge $500 or more About $500

    PIKSI (Developer Edition): Be the first to receive a Piksi. This hardware is identical to the Production Edition, but instead of shipping in December, will ship as soon as the campaign ends.

    Please note, two receivers are required to do RTK so the PIKSI reward on its own won't allow you to do centimeter level positioning.

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    Pledge $500 or more About $500

    PIKSI (Production Edition): Your very own Piksi GPS receiver from our first production batch. Please note, two receivers are required to do RTK so the PIKSI reward on its own won't allow you to do centimeter level positioning.

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    Pledge $900 or more About $900

    RTK KIT (Developer Edition): You'll be the first to receive a complete RTK setup. Two Piksi receivers (that will be identical to the Production Edition) and XBee radios to connect them. Instead of shipping in December, this reward will ship as soon as the campaign ends. Please note that the RTK software development may not be finished until December.

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    Pledge $900 or more About $900

    RTK KIT (Production Edition): Everything you need for an RTK setup. Two Piksi receivers from our first production batch and XBee radios to connect them.

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    Pledge $2,000 or more About $2,000

    Ruggedized RTK KIT with Bluetooth: A ruggedised version of our RTK KIT for use in the field, with Bluetooth connectivity, SD card storage, a lithium-polymer battery and an integrated radio. Everything you need to collect data in the field with your smartphone or set up a convenient base station for your UAV.

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Funding period

- (30 days)