Polaris Alpha User Manual
1
ALPHA RTK RECEIVER
USER GUIDE
Version 0.8
October 25, 2018
info@polaris-gnss.com
https://www.polaris-gnss.com
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Table of Contents
1. Overview ................................................................................................................ 3
1-1 Introduction ..................................................................................................... 3
1-2 RTK Operation Guidelines ................................................................................ 3
1-3 Alpha RTK Receiver Features……………………………………………………………………….4
2. Applications ............................................................................................................ 5
3. Description of Interfaces ........................................................................................ 6
3-1 Appearance ...................................................................................................... 6
3-2 Pinout of 6-Pin Connector ............................................................................... 7
3-3 Pinout of 4-Pin Connector ............................................................................... 7
3-4 Connector Cables for Alpha ............................................................................. 8
4. Application Scenarios ........................................................................................... 10
4-1 Special Short Baseline Experimental Setup ................................................... 10
4-2 RTK Survey and Data Collection ..................................................................... 11
4-3 Real-Time Precision Guidance ....................................................................... 13
4-4 Hardware Configuration Settings ................................................................... 16
5. Preparing for First Time Use ................................................................................ 17
5-1 RTK Viewer ..................................................................................................... 17
5-2 USB Driver ...................................................................................................... 17
5-3 Checking Alpha Receives Satellite Signal ....................................................... 17
6. RTK Setup ............................................................................................................. 19
6-1 Introduction ................................................................................................... 19
6-2 Configuring the Rover .................................................................................... 20
6-3 Configuring the Base ...................................................................................... 21
6-4 RTK Application Scenarios In Detail ............................................................... 25
7. Configure RTK License .......................................................................................... 41
8. Raw Measurement Recording and Post Processing ............................................. 42
9. Software Update .................................................................................................. 43
APPENDIX
A-1. Additional Software Configurations ..................................................................... 46
A-2. NTRIP Server/Caster Setup for Users Without Fixed IP ..................................... 48
A-3. NTRIP Server/Caster Setup for Users With Fixed IP ........................................... 51
A-4. Data Flow of the I/O Interface ........................................................................... 54
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1. Overview
1-1 Introduction
Alpha is a high performance RTK receiver with multiple interfaces, including UART, USB, and Bluetooth.
It offers centimeter-level positioning accuracy suitable for survey, mapping, GIS data collection, and
outdoors robotic precision guidance.
By default, Alpha is shipped as RTK rover to accept RTCM3.x message or SkyTraq carrier phase raw
measurement data from a RTK base, and provide centimeter-level accurate position result relative to
the RTK base in standard NMEA message format. Alpha can also be configured as a RTK base to
provide RTCM3.x message or SkyTraq carrier phase raw measurement data output.
Alpha has three major interfaces for different applications. The USB interface is mainly used for
configuration, monitoring, and supplying power. With Bluetooth V2.1+EDR module built-in, Alpha can
be used as external Bluetooth RTK receiver for Android Mobile Device to provide higher accuracy
positioning than internal GPS. The 3.3V LV -TTL UART interface allows simple connection to controllers
for precision guidance applications, replacing normal meter-level accuracy GPS receiver.
Alpha can easily connect and use with Pixhawk / ArduPilot using the supplied connector cable,
enabling UAV to navigate with centimeter-level position accuracy. Unique to Alpha is camera shutter
triggered RTK position stamp function, which is much more accurate than alternative time stamp
based linear interpolation approach to re-generate camera triggered position for aerial survey
application.
1-2 RTK Operation Guidelines
To provide centimeter-level RTK accuracy, Alpha requires much better operating condition than
conventional meter-level accuracy GPS receiver:
Baseline distance between base and rover should be under 10Km.
Open sky environment without interference and signal blockage
Received signal level should be no less than 40dB/Hz.
12 or more satellites over 15 degree elevation angle
Good satellite geometry with satellites spread over four quadrants of the sky.
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1-3 Alpha RTK Receiver Features
Base or Rover Mode Configurable Using RTK Viewer Utility
Supports L1 GPS/GLONASS or L1 GPS + B1 BDS RTK Operation
Supports LV-TTL UART / USB / Bluetooth V2.1+EDR Interface
Supports SDHC micro-SD Card for Data Logging Post Processing
RTK Position Accuracy 1cm + 1ppm
Maximum RTK Update Rate 10Hz
Supports RTCM 2.x / 3.x Messages
NMEA Output
Update Rates：1 / 2 / 4 / 5 / 8 / 10 Hz for RMC / GGA / VTG / PSTI-030
Messages：GGA / GLL / GSA / GSV / RMC / VTG / ZDA / PSTI
Baud Rate
Bluetooth：115200
UART / USB：4800 / 9600 / 19200 / 38400 / 57600 / 115200, default 115200
Current Consumption
180mA @ 5V
Weight：40 g
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2. Applications
Alpha RTK
Base
RTK
antenna
Alpha RTK
Rover
RTK
antenna
. . .
RTCM3.x / RAW
NMEA
Figure 2-1
Alpha RTK rover works with carrier phase measurement, using fractional part of ~19 centimeter wave
length GNSS signals and differential principles to achieve centimeter-level accuracy positioning with
respect to the RTK base.
Referring to figure 2-1, Alpha RTK base antenna is set at a fixed location, with antenna location
coordinates already a known reference, or surveyed by method described in later section. It receives
signals from GPS/GLONASS or GPS/BDS satellites, generates correction data in RTCM3.x or SkyTraq
raw measurement format, and sends it to remote Alpha RTK rover through wireless channel. The rover
uses this correction data along with signals received from satellites to calculate the precise position of
the RTK rover antenna, and output antenna position / velocity / time information in NMEA-0183
format. Correction data from the one RTK base can be sent to an unlimited number of RTK rovers.
The Alpha RTK receiver is suitable for, but not limited to, following applications:
Surveying and GIS data collection with Android mobile device
Precision farming machine guidance
Precision grass cutting machine guidance
Precision guidance of unmanned aerial vehicles (UAV)
Aerial survey RTK position stamping without need of ground control points
Precision tracking of vehicle dynamics
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3. Description of Interfaces
3-1 Appearance
Figure 3-1
No.
Description
1
SMA connector for RTK antenna.
2
Status LED. There are three states shown for Alpha as Rover
1. Base data not received: flashes two times followed by 1 sec of silence.
2. In process of finding RTK solution: flashes with frequency at 1Hz or 4 Hz depends on the RTK
ratio is in between 1 and 3 or in between 3 and 5.
3. RTK solution found: remain lighted continuously.
This LED is always off when Alpha is configured as Base.
3
LED for indicating the TTL UART interface is selected.
4
LED for indicating the USB interface is selected.
5
LED for indicating the Bluetooth interface is selected.
6
Push button for interface selection. Each time the button is clicked, the selected interface toggles.
Press this button for more than 3 seconds will enable/stop logging measurement data to SD Card.
7
Slide switch for choosing the operating mode, see section 4-4 for details.
8
6-pin TTL connector for Base-to-Rover or Rover-to-UAV applications, see section 3-2 for details.
9
Micro USB connector
10
SD card status LED. When the SD card is inserted, this LED will flash and record raw measurement
data to the SD card, until number of files on the SD card reaches 129. In this case the LED lights up
continuously, and recording stops. If no SD card is inserted, the LED is off.
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Micro SD card connector for raw measurement data recording.
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4-pin TTL connector for aerial survey applications. See section 3-3 for details.
Table 3-1
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3-2 Pinout of 6-Pin Connector
1 62 3 4 5
Figure 3-2
The red spot indicates the top side.
No.
Description
I/O
Voltage
Min
Max
1
Power input to Alpha when USB connector power unconnected
Power output from Alpha if USB connector power is connected
PWR
3.3V
4.6V
5.5V
5.0V
2
UART input for base data, RTCM3.x or SkyTraq raw
measurement format
IN
3.0V
3.6V
3
UART output for NMEA message
OUT
3.0V
3.3V
4, 5
NC 6
Ground
PWR
Table 3-2
3-3 Pinout of 4-Pin Connector
1 234
Figure 3-3
The red spot indicates the top side
No.
Description
I/O
Voltage
Min
Max
1
DC power output from Alpha to external device
OUT
3.1V
3.3V
2
1PPS (1 pulse per second) output signal
OUT
3.1V
3.3V
3
External camera trigger input signal
IN
1.5V
5.0V
4
Ground
IN
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Table 3-3
3-4 Connector Cables for Alpha
There are several types of connector cable supplied with the Alpha RTK Kit for different applications.
3-4-1 Wire for connecting Base-to-Rover (for base/rover pair short baseline testing)
Black
Yellow
White
6-pin Connector 6-pin Connector
Figure 3-4
3-4-2 Wire for connecting Rover-to-UAV
Black
Blue
Green
Yellow
White
Red
6-pin Connector 6-pin Connector
Figure 3-5
3-4-3 Wire for connecting Rover-to-Camera
Black
Green
White
Red
4-pin Connector 4-pin Connector
Figure 3-6
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3-4-4 Wire for 6-pin TTL connector with pitch 2.54 Dupont Lines
Black
Blue
Green
Yellow
White
Red
6-pin Connector
Black
Blue
Green
Yellow
White
Red
2.54 Dupont Female
Connector
Figure 3-7
3-4-5 Wire for 4-pin TTL connector with pitch 2.54 Dupont Lines
Black
Green
White
Red
4-pin Connector
Black
Green
White
Red
2.54 Dupont Female
Connector
Figure 3-8
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4. Application Scenarios
4-1 Special Short Baseline Experimental Setup
Base
TTL mode / switch on A
Rover
TTL mode / switch on B
Micro-USB
cable
Micro-USB
cable
6-pin 3 wire for Base-to-Rover (sec. 3-4-1)
Setup for Special Short Baseline Experiment
RTK
antenna
RTK
antenna
. . .
Alpha RTK Alpha RTK
Figure 4-1
For users setting up a local RTK base for use with RTK rover, this experimental setup allows quickly
becoming acquainted with all aspects of Alpha RTK receiver operation. Using our RTK Viewer
Windows-PC software, users can configure Alpha to be base or rover; see section 6 for details.
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Figure 4-2
4-2 RTK Survey and Data Collection
Internet
Bluetooth
Rover
BT mode / switch on B
3rd Party RTK Base
with NTRIP caster
NTRIP
client
3G/4G/LTE
Setup for GIS Data Collection
RTK
antenna
. . .
Alpha RTK
Figure 4-3
When used with Trimble or Leica RTK base station within 10Km distance, or Trimble or Leica RTK base
station with Virtual Reference Station (VRS) service as shown in figure 4-3 for RTK survey and data
collection, then only one Alpha RTK receiver is needed. It’s configured as RTK rover and connects to an
Android smartphone via Bluetooth. User can then run the free Lefebure NTRIP Client App on the
smartphone for retrieving 3rd-party RTK base station data over Internet and sending it to the Alpha
RTK receiver. With “MOCK Location” option enabled on the smartphone, GPS related location Apps on
the smartphone will be able to use the more accurate position from Alpha RTK receiver.
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Base
USB mode / switch on A
Micro-USB
cable
Internet
Bluetooth
Rover
BT mode / switch on B
NTRIP
caster
NTRIP
client
3G/4G/LTE
Setup for GIS Data Collection
RTK
antenna
RTK
antenna
. . .
Alpha RTK Alpha RTK
Figure 4-4
In case of setting up a local RTK base with known reference location as shown in figure 4-4 for RTK
survey or data collection, one Alpha RTK receiver is configured as RTK base connecting via micro-USB
port to a computer running NTRIP Server/Caster, and another Alpha RTK receiver is configured as RTK
rover connecting via Bluetooth to an Android smartphone. User can run the free Lefebure NTRIP
Client App on the smartphone to retrieve the Alpha RTK base data over Internet and sending it to the
Alpha RTK rover. With “MOCK Location” option enabled on the smartphone, the GPS related location
Apps on the smartphone will be able to use the more accurate position from Alpha RTK rover.
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4-3 Real-Time Precision Guidance
Base
USB mode / switch on A
Micro-USB
cable
Mission Planner
RTK
antenna
Telemetry
Radio
Telemetry
Radio
Rover
TTL mode / switch on B
RTK
antenna
6-pin wire for
UAV-to-Rover
Setup for UAV
433MHz/915MHz/2.4GHz
Alpha
RTK
Alpha
RTK
. . .
Figure 4-5
When using Alpha RTK receiver in Unmanned Aerial Vehicle (UAV) applications as shown in figure 4-5,
one Alpha is configured as RTK base connecting via micro-USB cable to a computer running Mission
Planner, the computer is also connected with a telemetry radio to communicate with another
telemetry radio installed on the UAV. A second Alpha is configured as RTK rover, connecting to the
autopilot of the UAV via a 6-pin 6 wire cable provided along with the Alpha RTK Kit. In this application
scenario data from RTK base is encapsulated in MAVLink injection protocol sent to autopilot of the
UAV, and autopilot then relays the data to RTK rover, the NMEA message output from RTK rover is sent
to autopilot of the UAV for precision guidance.
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Base
USB/TTL mode / switch on A
TTL or Micro-USB
RTK
antenna
Telemetry
Radio
Telemetry
Radio
Rover
TTL mode / switch on B
RTK
antenna
Pin #2 of 6-pin
TTL connector
Setup for Real-Time Controller over Telemetry Radio
433MHz/915MHz/2.4GHz
Alpha RTK
Alpha
RTK
. . .
Real-Time
Controller
Pin #3 of 6-pin
TTL connector
Figure 4-6
For line-of-sight precision guidance applications that do not use Mission Planner with MAVLink
protocol as in figure 4-6, user can configure one Alpha RTK receiver as RTK base and use 6-pin UART
connector port or micro-USB port to connect to a telemetry radio for sending correction data to the
RTK rover. Another Alpha RTK receiver is configured as RTK rover, using pin-2 of the 6-pin connector to
connect to another telemetry radio for receiving correction data from the RTK base, and using pin-3 of
the 6-pin connector to send RTK NMEA message output to the real-time controller.
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Base
USB mode / switch on A
Micro-USB
cable
Internet
Bluetooth
Rover
BT mode / switch on B
NTRIP
caster
NTRIP
client
3G/4G/LTE
RTK
antenna
RTK
antenna
. . .
Alpha RTK
Alpha RTK
Setup for Real-Time Controller over Internet
Real-Time
Controller
Pin #3 of 6-pin
TTL connector
Figure 4-7
A smartphone can be used to connect RTK rover with RTK base over Internet instead of using a pair of
telemetry radios for non-line-of-sight real-time precision guidance application as shown in figure 4-7.
In this case user can setup an Alpha RTK base as described previously with figure-4-4, and with Alpha
RTK rover also connecting pin-3 of the 6-pin connector to the real-time controller’s UART input for
sending the NMEA output messages to the real-time controller.
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4-4 Hardware Configuration Settings
Table 4-1 shows push button and slide switch configuration settings for Alpha RTK receiver in different
application scenarios. For each usage scenario, V indicates which of the TTL / USB / Bluetooth
interface should be selected to have Alpha’s LED light up, A or B indicates which position to put
Alpha’s slide switch. The boldface Output indicates which NMEA output interface is used for this
usage scenario. The boldface Input indicates which input interface used by rover to receive base data.
Table 4-1
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5. Preparing for First-Time Use
5-1 RTK Viewer
RTK Viewer is a Windows-based software for configuring or monitoring Alpha RTK receiver. User can
download the software from below link:
https://www.polaris-gnss.com/rtk-viewer.zip
5-2 USB Driver
USB driver from Silicon Labs may need to be installed:
https://www.silabs.com/products/development-tools/software/usb-to-uart-bridge-vcp-drivers
5-3 Checking Alpha Receives Satellite Signal
Below steps bring up Alpha as normal GPS receiver to receive satellite signal:
Connect antenna to the Alpha SMA connector and place antenna at a window side having good
sky view. Put Alpha’s slide switch to A position.
Open RTK Viewer. Connect Alpha to PC using micro-USB cable. A dialog box for COM port and
baud rate will appear. Click “Connect”.
Figure 5-1
Click Alpha’s push button to select USB interface. NMEA output should be seen on the Message
screen. If having good sky view with sufficient number of satellites tracked, the signal bar will
turn solid and have position fix.
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