GPS/GNSS Measurement and Data Acquisition

Course overview

The course lays the foundation for precise geospatial data acquisition using DewesoftX. It begins with a thorough explanation of GNSS principles—from satellite systems (GPS, Galileo, etc.) and signal structure to positioning computation through trilateration and pseudorange techniques. You’ll also delve into augmentation methods like SBAS, DGNSS, and RTK, which reduce positional errors significantly.

Next, you will explore hardware solutions, including Dewesoft’s DS-MU1 GNSS receiver and inertial-assisted GNSS devices. You’ll learn how these connect via USB, CAN, or Ethernet, manage PPS/IRIG signals, and offer robust performance in rugged environments.

The software section focuses on DewesoftX integration: adding the GNSS acquisition module, selecting input interface and data sentences, setting baud rate, and activating channels such as position, speed, HDOP, and satellite count. You’ll configure timestamp synchronization to align GNSS with analog and digital data streams.

Hands-on exercises include initiating GNSS measurements in Measure mode, tracking live satellite data with sky plots, and displaying navigation results in map widgets. You’ll record GNSS data alongside other DAT—video, analog signals—for synchronized analysis. In Analyze mode, you’ll replay data with map overlays, timeline navigation, and export options for further geospatial use.

By the end of the course, you will be comfortable configuring GNSS modules in DewesoftX, synchronizing GNSS data with other domains, and producing accurate, location-tagged datasets ideal for vehicle dynamics, mobile testing, outdoor field analysis, and multi-domain research.

The Global Navigation Satellite System (GNSS) is a space-based system of satellites that provide location (longitude, latitude, altitude) and time information in all weather conditions, anywhere on or near Earth, as long as there is an unobstructed line of sight to four or more GNSS satellites.

Currently, two GNSS systems have full global coverage:

• GPS (Global Positioning System) – Developed by the United States, GPS consists of at least 24 operational satellites orbiting the Earth. It is currently the world’s most widely used satellite navigation system.

• GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistema) – The Russian navigation system, which consists of 31 satellites, of which 24 are operational.

Two additional global navigation systems are under construction:

• BeiDou Navigation Satellite System – The Chinese GNSS, currently consisting of 22 operational satellites in orbit. It already provides regional positioning services in the Asia-Pacific region. Global operational capability with 35 satellites is expected by 2020.

• Galileo – The European GNSS, with 18 satellites currently in orbit. It is expected to reach full operational capability by 2020.

GPS basics

True range multilateration, or trilateration, is the basic concept behind GNSS position calculation. GNSS satellites transmit signals that contain a fast, periodic synchronization code and a slower navigation message. The synchronization code is used to determine the time it takes for the signal to reach the receiver. The navigation message contains information about the satellite’s position in space, its clock time, system health, and data about surrounding GNSS satellites.

Signals from at least four satellites are required for the receiver to calculate its position, although in practice more than four satellites are typically used to improve accuracy.

2D concept

It is easier to visualize the concept of trilateration in two dimensions. A GNSS receiver calculates its distance to a satellite based on the signal reception delay. Since the satellite’s position at the time of transmission is known (derived from the slower navigation message), the receiver’s position can be located anywhere along the circle defined by that distance around the satellite.

If another satellite with a known position and distance from the receiver is added, then there are two possible positions where the receiver could be located.

This would be enough to place the receiver in 2D space, but to determine the exact position, a third satellite is required. In real-world navigation, however, two possible positions are usually sufficient, since one of them is normally either in space or deep below the Earth’s surface.

The third satellite in 2D is also needed to eliminate the receiver clock error. Range measurement errors can occur, and clock error is one of the largest contributors. When a receiver gets a signal, it calculates its delay by comparing the transmission time of the signal with the reception time. This delay depends on the receiver’s clock, which is usually not as precise as the satellite clocks. Even though the receiver clock is frequently synchronized to GNSS time during operation, small timing errors still occur.

Distances from delays are calculated using the speed of light (299,792,458 m/s). Even very small timing errors can cause large positioning errors—for example, an error of 1 millisecond can result in a position error of 300 km. However, this error can be corrected by using an additional satellite, since the receiver clock error is the same for all signals received at approximately the same time.

3D concept

In 2D, two satellites are required to determine the receiver’s position, with an additional satellite needed to correct the receiver clock error. To determine a position in 3D space, one more satellite is required.

If the distance to a satellite is known from the signal delay, the receiver could be located anywhere on the sphere around that satellite, with the radius equal to the calculated distance.

With two satellites, the receiver could lie anywhere on the circle formed by the intersection of the two spheres.

Adding a third satellite reduces the possible locations to two points.

As mentioned earlier, two possible positions are sufficient to determine the receiver’s location in 3D space. For example, if Position 1 (from the figure above) lies on the Earth’s surface, then Position 2 would be somewhere in space at a higher altitude than the GNSS satellites. However, a fourth satellite is required to correct the receiver clock error.

Each receiver measures the range between itself and the transmitting satellite. However, the measured range derived from the signal delay is not exact and contains errors. This measured range is called a pseudorange. With various corrections, these pseudoranges can be adjusted to more closely approximate the true range and can then be used to calculate an accurate receiver position.

• RjR^jRj – Pseudorange between the GNSS receiver and the satellite at the time of transmission, calculated from the signal delay

• ρj\rho^jρj – True geometric distance between the GNSS receiver and the satellite at the time of transmission

• ccc – Speed of light (299,792,458 m/s)

• δtrec\delta t_{rec}δtrec​ – Receiver clock error

• δtsatj\delta t^j_{sat}δtsatj​ – Satellite clock error

• TjT^jTj – Tropospheric signal delay

• α^Ij\hat{\alpha}I^jα^Ij – Ionospheric signal delay

• TGDjTGD^jTGDj – Instrumental delay

• MjM^jMj – Multipath error

• eje^jej – Receiver measurement noise

Navigation equations

Each pseudorange is the sum of the true distance to the satellite and various error components. The true distance can be expressed as the distance between the unknown receiver coordinates and the known satellite coordinates.

\(x_{rec}, y_{rec}, z_{rec}\) - unknown receiver coordinates

\(x^j_{sat}, y^j_{sat}, z^j_{sat}\)

All errors, except for the receiver clock error, depend on the satellite’s position relative to the receiver at the time of transmission. These errors are typically corrected using mathematical models.

The pseudorange can then be expressed using the previously defined terms.

The DjD^jDj term is resolved through error models and can be considered a known value, which allows it to be moved to the left side of the equation.

There are now four unknown variables in the range equations: the receiver coordinates (xrec,yrec,zrec)(x_{rec}, y_{rec}, z_{rec})(xrec​,yrec​,zrec​) and the receiver clock error δtrec\delta t_{rec}δtrec​. Therefore, at least four pseudorange measurements from different satellites are required to solve for these variables (a system of four equations with four unknowns).

In practice, more than four satellites are usually used. This produces an overdetermined system (more equations than unknown variables), and the solution is obtained as the best fit to the navigation equations.

GNSS satellites transmit two or more radio signals. Each signal has its exact carrier frequency, which carries two components: a fast ranging code signal and a slower navigation data signal. These two signals are multiplexed onto the carrier. Both are modulated onto the carrier using binary phase-shift keying (BPSK), where binary 1 corresponds to a different carrier phase than binary 0.

• The carrier signal is an electromagnetic signal at a specific frequency within the radio frequency range (approximately 20 kHz to 300 GHz).

  The ranging code is a sequence of 0s and 1s (zeros and ones) that enables the receiver to determine the travel time of the radio signal from the satellite to the receiver. Ranging codes are also known as Pseudo-Random Noise (PRN) sequences or PRN codes.

  The navigation data is a binary-coded message that provides information such as the satellite’s position (ephemeris), clock bias parameters, the positions of other satellites in the constellation (almanac), satellite health status, and other supplementary information.

Current GNSS systems transmit multiple radio signals that differ in both their frequency band and signal structure. All of these signals can be used for ranging, but some do not provide any navigational data. Such signals are primarily used as supplementary inputs to help reduce errors caused by ionospheric delays.

Most GNSS systems also transmit signals that are restricted to authorized users, such as the military or government agencies.

The pseudorange is determined by the delay between signal transmission and signal reception. This delay can be measured using either the ranging code or the carrier signal.

Code based positioning

The ranging code is a binary pseudo-random sequence that is periodically transmitted by each satellite. For example, in the GPS L1 signal, this pseudo-random code repeats every millisecond. The GNSS receiver generates the same pseudo-random code as the one transmitted by the satellite.

The receiver then compares its internal code with the received satellite code. Because of the distance between the satellite and the receiver, the two codes are not aligned. To determine the signal’s travel time, the receiver delays its own pseudo-random sequence until it aligns with the received sequence.

Binary pseudo-random sequences are composed of chips, which are similar to bits but do not contain any data. These chip sequences are specifically designed so that alignment (or misalignment) can be easily detected.

For the GPS L1 signal, the chip duration is about 1 microsecond. If the receiver’s sequence is misaligned by one chip, the resulting range error is approximately 300 meters. This is because, at the constant speed of light, 1 microsecond of travel time corresponds to about 300 meters of distance traveled by the signal. Precise GNSS receivers typically achieve a misalignment of only 1–2% of the chip duration, which corresponds to a ranging error of 3 to 6 meters.

Carrier based positioning

Carrier-based positioning uses the carrier wave to determine the range. The wavelength of carrier signals is significantly shorter than the chip duration of ranging codes.

For example, the GPS L1 range code frequency is 1.023 MHz, with a chip duration of about 1 millisecond, resulting in an accuracy of 3 to 6 meters with precise receivers. By contrast, the carrier frequency of the GPS L1 signal is 1575.42 MHz—around 1500 times higher than the code frequency—with a wavelength of approximately 19 centimeters.

If both the exact number of wavelengths and the signal phase were known, positioning accuracy in the millimeter range could be achieved. However, due to the periodic nature of the sinusoidal carrier signal, the comparison between the internally predicted signal and the received signal produces the same solution for each cycle—this is known as signal ambiguity. Another unknown factor is the signal phase at the time of transmission from the satellite.

Carrier-based positioning can be achieved using the Real-Time Kinematics (RTK) technique or the Precise Point Positioning (PPP) technique. Both methods combine code-based and carrier-based positioning principles. In addition, carrier phase or frequency tracking is sometimes used to correct or smooth code-based pseudorange measurements.

The GNSS navigation message is transmitted on the same signal as the ranging code but at a slower rate. For example, the GPS navigation message is modulated along with the ranging codes at a rate of 50 bit/s. It is divided into five subframes, each 300 bits long. Therefore, it takes about 30 seconds to receive the complete navigation message.

In general, navigation messages provide information such as clock corrections, satellite positions, satellite telemetry, and details about other satellites in the constellation.

GPS navigation message

Telemetry and Handover Words

• This section contains information about the satellite status, an indication of its health, and the satellite time. The receiver uses this part of the message to synchronize its time with GPS time and to determine whether it should use the signal from the transmitting satellite.

Satellite Clock – GPS Time Reference

• This section contains information on GPS time (number of weeks since a specified date and the number of 1.5-second intervals since the start of the week) and the relationship between GPS time and satellite time (used for satellite clock error corrections).

Ephemeris

• This section provides precise information on the satellite’s orbit shape and orientation, as well as its velocity and position at a specified time. The receiver uses this data to calculate the satellite’s position at the time of transmission. Because position accuracy depends on the accuracy of the ephemeris data, updates are provided every two hours. Ephemeris data has a limited validity period and cannot be used once it is outdated.

• Almanac
  The almanac contains coarse orbit data for all the satellites in the constellation, as well as information for ionospheric delay corrections. Coarse orbital data helps the receiver locate satellites in view. In newer receivers, however, this feature is less critical than it once was. Ionospheric delay data is primarily used by receivers that can only operate on a single GNSS frequency.

  Because of the large amount of data, 25 navigation messages are needed to transmit the entire almanac. At 30 seconds per message, it takes about 12.5 minutes to transfer the complete almanac.

Time to first fix - TTFF

Time to First Fix (TTFF) is the time required by a receiver to obtain its first position fix after being switched on. There are three common TTFF scenarios:

• Cold Start: No data is stored in the receiver. The position solution is calculated through a full sky search of satellites without any almanac data. For the first position fix, the receiver requires satellite clock corrections, GNSS time reference, and ephemeris data from at least four satellites. Cold start TTFF depends directly on the navigation message transmission rate. In good GNSS environments (open sky view), cold start TTFF can be as low as 30 seconds, but it may take significantly longer if satellite reception is poor or interrupted. Cold start times can be greatly reduced with assisted GNSS (A-GNSS), where navigation data and approximate location are received through a higher-bandwidth source such as a mobile network or WLAN.

• Warm Start: The receiver has valid ephemeris and clock correction data but needs to retrieve the GNSS time reference from the navigation message to obtain a fix.

• Hot Start: The receiver has valid ephemeris, clock correction, and GNSS time reference. In addition, its approximate position and clock error are already known. In this case, the position can be calculated without waiting for information from the navigation message.

Satellite Clocks

• The nature of GNSS measurements requires highly accurate absolute timekeeping by each satellite. An error of just 10 nanoseconds in satellite time measurement results in a 3-meter error in the pseudorange to that satellite. Despite the use of atomic clocks onboard, satellite time still drifts and must be monitored against even more accurate atomic clocks at ground control stations. A clock correction model is periodically updated and applied in position calculations. Nevertheless, satellite clock errors can still cause a mean error of about ±2 meters in range measurements (GPS). These errors can be further reduced through more precise measurements, advanced clock modeling, or differential GNSS techniques.

Ephemeris Errors

• Ground control stations track satellite orbits and predict their near-future positions. Orbit parameters are frequently updated (every 2 hours for GPS) and have a limited validity period (about 4 hours for GPS). Orbital changes due to gravitational effects can be accurately predicted, but variability in solar radiation pressure introduces most of the errors. Ephemeris errors typically cause a mean error of ±2.5 meters in range measurements (GPS). These errors can be corrected using differential GNSS techniques.

Ionospheric Delays

• The ionosphere is a layer of the atmosphere extending from about 60 km to 2,000 km above the Earth’s surface. It contains a partially ionized medium created by the Sun’s ionizing radiation (UV and X-ray) and charged particles. The propagation speed of GNSS signals depends on the electron density of the ionosphere. During the day, electron density increases due to solar radiation; at night, free electrons recombine with ions, reducing density.

  GNSS signals are delayed in the ionosphere, and this delay is proportional to both electron density and signal frequency. The mean range error is about ±5 meters, but errors can be greater during periods of high ionospheric activity.

  Mitigation techniques:

  • Dual-frequency receivers: Compare measurements from two frequencies transmitted by the same satellite. Since ionospheric delay depends on frequency, the range error can be estimated and corrected.

  • Differential GNSS: A fixed base station measures ionospheric delay and transmits correction data via a communication network. Accuracy depends on the distance between the base station and the receiver.

  • Ionosphere modeling: Mathematical models are used to estimate delays, ranging from simple empirical models to complex numerical simulations. Single-frequency receivers typically use empirical models, with coefficients updated regularly (often provided by GNSS augmentation systems).

Tropospheric Delays

• The troposphere is the lowest layer of the atmosphere, closest to the Earth. Air humidity, atmospheric pressure, and temperature affect GNSS signal propagation speed. Delays due to humidity are similar to ionospheric delays but harder to correct, since they are highly local, change rapidly, and are not proportional to signal frequency. These delays can only be mitigated using differential GNSS techniques.

  By contrast, the effects of atmospheric pressure and temperature can be effectively corrected with mathematical models. For GPS, uncorrected tropospheric delays can cause a mean error of about ±0.5 meters in range measurements.

Multipath Errors

• Multipath errors occur when GNSS signals reach the receiver by multiple paths due to reflections from surrounding surfaces or when the direct line-of-sight to the satellite is blocked (non-line-of-sight reception).

  • Multipath interference: Occurs when signals are reflected and distort the pseudorandom code, leading to errors in range measurements.

  • Non-line-of-sight reception: Happens when only a reflected signal is received because the satellite is not directly visible.

  Mitigation techniques:

  • Specialized receiver algorithms to detect and filter multipath interference.

  • Antenna designs that reduce sensitivity to reflected signals.

  • Use of multiple antennas or antennas that measure the signal’s arrival angle.

  • Integration with cameras or environmental sensors to detect objects that could cause non-line-of-sight errors.

• Instrumental delays
  These delays are caused by instrument circuitry, cables, antennas, and internal filters used in both receivers and satellites. While receiver instrumental delays are accounted for in the receiver clock calculation, satellite instrumental delays can be corrected either with additional data or by using dual-frequency receivers. Dual-frequency receivers calculate the delay by comparing the difference in range measurements across two signals.

  Single-frequency receivers, on the other hand, use a total satellite group delay that is included in the navigation message to reduce the error. Satellite instrumental delays affect both code-based and carrier-based measurements and are proportional to the satellite signal frequency.

All GNSS augmentation systems provide additional data to GNSS receivers, either to improve solution accuracy or to increase integrity.

SBAS - satellite-based augmentation systems

SBAS are civil aviation safety-critical systems that support wide-area augmentation. These systems consist of ground stations and geostationary satellites. The ground station infrastructure computes the integrity of GNSS constellations, correction data, and SBAS satellite ranges. This information forms the SBAS signal-in-space, which is transmitted by SBAS geostationary satellites. Receivers that support SBAS use this signal to:

• Compute the range to SBAS satellites, increasing the number of usable satellites.

• Reduce ionospheric error using ionospheric model coefficients provided in the SBAS message.

• Reduce GNSS constellation clock errors with SBAS clock corrections.

• Calculate the integrity of the GNSS solution.

The primary purpose of SBAS is to increase the integrity of GNSS systems. However, with the additional data, position accuracy is also improved to about 1 m (1 sigma). WAAS and EGNOS are certified for use in both horizontal and vertical guidance during various flight operations, including landing approaches.

GBAS - ground-based augmentation system

The primary purpose of GBAS is to provide integrity and safety for GNSS services in aviation during approach, landing, departure, and surface operations. Its role is similar to SBAS, with the main difference being that GBAS provides only local corrections.

A typical GBAS installation consists of two or more fixed GNSS receivers that compute correction data and assess the integrity of the GNSS service. The differential data, integrity parameters, and final approach segment data are broadcast over very high frequency (VHF). This data can be used by any aircraft within the coverage area.

GBAS improves GNSS position accuracy to about 1 m (1 sigma).

DGNSS - differential GNSS 

Differential GNSS (DGNSS) techniques use a network of fixed reference stations, known as base stations, to correct for satellite clock bias errors, ionospheric delays, and tropospheric delays. This correction data is transmitted over a network and used by mobile receivers, called rovers, to improve positioning accuracy. However, differential techniques cannot remove errors caused by multipath or receiver noise. Unlike SBAS or GBAS, DGNSS networks do not provide integrity assurance. It is also important to note that differential techniques depend on the accuracy of the base station’s known coordinates.

The standard differential technique (DGNSS) calculates errors from code-based pseudorange measurements at fixed reference stations. The method takes advantage of the fact that errors are similar if the rover is located near the base station. Typical DGNSS accuracy is about 1 m (1 sigma) but degrades at a rate of roughly 0.5 m for every 100 km of distance from the base station.

Differential correction data is usually transmitted over radio frequencies or via the mobile network. Because error variations change slowly, the correction data does not need to be updated in real time. DGNSS networks can be deployed as wide-area systems or local setups, where a DGNSS receiver operates in base station mode and transmits differential corrections via a data link.

RTK - real time kinematics 

Real-Time Kinematic (RTK) is a highly accurate GNSS differential technique that uses carrier phase tracking to achieve positioning accuracy of about 1 cm near the base station. RTK requires a base station and a rover equipped with code range measurement, carrier phase tracking capabilities, and a real-time data link. The data link (via radio transmission or mobile network) transmits base station coordinates, code ranges, and carrier phase measurements to the rover in real time.

The rover resolves carrier phase ambiguity by minimizing differences between base station and rover ranges measured with multiple satellites. This process also fully removes satellite clock delays, but it is only effective if measurements at the base station and the rover are performed at nearly the same time. Initial ambiguity resolution typically takes around 10 seconds with modern dual-frequency receivers under clear, open-sky conditions, but it may take longer depending on factors such as satellite visibility, multipath effects, or receiver type.

RTK Requirements for Fix Solutions

To acquire and maintain a valid RTK fix, the following conditions must be met:

• Only satellites visible to both the base station and the rover can be used in the RTK calculation. RTK receivers typically require at least five common satellites.

• Signal obstructions that cause multipath or loss of satellite visibility can result in loss of RTK fix and may require partial or even full recalculation of cycle ambiguities.

• RTK solutions are generally valid within 15–20 km of the base station, but coverage can be extended up to 80 km using a network of RTK base stations (NRTK).

The RTK technique can also be used to determine accurate relative positions by employing a movable base station. The absolute accuracy of this system is limited by the accuracy of the moving base station, but centimeter-level relative accuracy between the base station and the rover is still achievable. Movable base techniques are commonly used in ADAS (Advanced Driver Assistance Systems) testing, where the relative position between two vehicles must be measured.

WARTK - wide area real time kinematics

Wide Area Real-Time Kinematics (WARTK) is a relatively new technology designed to extend RTK-level accuracy to distances of up to 500 km around WARTK base stations. This is achieved through a combination of RTK correction data and highly accurate ionospheric information. Currently, there are no operational WARTK systems.

PPP - precise point positioning

Precise Point Positioning (PPP) enables centimeter-level accuracy without requiring a nearby base station. This is made possible by using precise satellite clock and ephemeris information in real time (via satellite downlink or mobile network). PPP receivers must support dual-frequency ranging and carrier phase tracking.

Ionospheric errors are compensated using dual-frequency measurements, while additional processing allows the PPP algorithm to also compensate for tropospheric errors, estimate carrier phase ambiguity, and achieve centimeter-level accuracy. Currently, initialization to centimeter accuracy with PPP takes significantly longer—on the order of tens of minutes—compared to RTK. However, PPP techniques for real-time applications are still under development. With shorter initialization times, PPP could become a more cost-effective alternative to RTK, which requires a nearby base station.

For now, PPP techniques are primarily used for GNSS data post-processing.

Dewesoft offers a range of GNSS devices designed for different applications and accuracy requirements. The flexibility of DewesoftX software also allows the integration of third-party GNSS devices.

Dewesoft GNSS devices

You can find an overview of all Dewesoft navigation instruments with GNSS receivers on the navigation instruments webpage.

DS-VGPS-HS and DS-VGPS-HSC

• Multi-purpose GNSS device with a 20/100 Hz GNSS receiver.

• RTK option available (2 cm positioning accuracy; supports both base and rover modes; dual-frequency GPS L1, L2 and GLONASS L1, L2).

• Interfaces: USB, RS232 (DS-VGPS-HS), and CAN output (DS-VGPS-HSC).

• External trigger switch input for synchronization.

• External display available for in-vehicle use.

• PPS output for device synchronization.

DS-CLOCK

• synchronization box with GNSS receiver

• 10 Hz position update rate, SBAS augmentation supported.

  Internal clock can be driven either by an external IRIG time signal or by the internal GNSS receiver clock.

  Generates IRIG B-DC signals for synchronization.

DS-IMU1

• GNSS-supported inertial measurement platform for measuring orientation, position, velocity, and acceleration.

  Supports SBAS and DGNSS augmentation (for details, refer to the DS-IMU Gyro Manual).

  PPS output for device synchronization.

NAVION i2

• GNSS-supported inertial measurement platform for measuring orientation, position, velocity, and acceleration.

  Ethernet-based, enabling remote connection to the system directly via DS-WIFI4.

  Dual-frequency GNSS receiver.

  Supports RTK (1 cm position accuracy), DGNSS, and SBAS augmentation.

  Dual GNSS antenna measurement for accurate static heading output.

  PPS output for device synchronization.

GNSS receiver in SBOX and MINITAUR.

• SBOX and MINITAUR devices can be equipped with different GNSS receivers:

  • 10 Hz NVS GPS/GLONASS receiver, or

  • 20/100 Hz L1/L2 GPS/GLONASS Topcon receiver (also supports RTK and other augmentation systems).

Supported 3rd party GNSS devices in DewesoftX

• Every NMEA compatible GNSS device,

• Topcon GNSS,

• Novatel GNSS,

• Racelogic V-BOX,

• Microsat,

• Dewetron V-GPS.

A GNSS receiver can also be used as a precise timing source for instrument synchronization. Most receivers support a PPS output, and some can also generate IRIG time codes.

Pulse per second (PPS)

Pulse Per Second (PPS) is an electrical signal consisting of pulses shorter than one second that are accurately repeated once every second. Devices adjust their clocks according to the PPS signal. The accuracy of PPS signals depends on the implementation. For example, PPS timing accuracy on commercial GNSS receivers is typically around ±25 ns.

All Dewesoft navigation instruments include a PPS output option. With a PPS signal, you can directly synchronize Dewesoft USB devices such as the DEWE-43 or SIRIUS USB. Dewesoft EtherCAT devices can be synchronized using the ECAT Sync Junction, which supports PPS input and synchronizes all Dewesoft EtherCAT devices connected to the network.

IRIG time code

Inter-Range Instrumentation Group (IRIG) time codes are standardized formats for transferring timing information. IRIG signals are structured as data frames with absolute time information that are sent periodically at a specified rate. There are six IRIG time code formats, designated A, B, D, E, G, and H, each differing in the rate of data frame transmission. IRIG signals can also be implemented in three different hardware forms (different modulation types).

Among Dewesoft navigation instruments, the DS-CLOCK can generate IRIG-B DC-modulated time codes from its internal GNSS receiver. The DS-CLOCK can also convert IRIG A, B, and G (DC or AC modulated) into IRIG-B DC signals. IRIG-B DC time code input is directly supported by DEWE-43, SIRIUS, and DS-NET devices for synchronization. It is also supported by the ECAT Sync Junction for synchronizing Dewesoft EtherCAT devices.

To use GNSS devices with Dewesoft X, they must first be added to the Dewesoft device setup. The procedure differs depending on the device.

DS-VGPS-HSC and DS-CLOCK

Both devices feature a Dewesoft USB interface, which enables Dewesoft X to automatically recognize them when connected. If automatic detection is unsuccessful, the devices can be manually added in the Dewesoft X Settings.

If the unit does not appear in the Devices menu, device recognition can be triggered by clicking the Refresh button.

Device settings can be accessed by selecting the device from the device list.

Embedded GNSS receivers and DS-VGPS-HS

Receivers embedded in SBOX or MINITAUR, as well as the DS-VGPS-HS, are connected to the computer via the RS232 interface. They can be added in the Dewesoft X device settings by clicking the Add button.

When the Add Device menu opens, select the Dewesoft RS232 (Topcon/Javad/NVS) option.

DewesoftX then adds the device to the current system configuration and automatically scans for GNSS receivers connected to the computer. After a successful scan, the receiver settings appear in the Device Settings menu. The available settings vary depending on the receiver type and its configuration options.

NAVION i2 and DS-IMU1

Both GNSS-supported inertial navigation units are supported in DewesoftX through the Navion and DS_IMU plugins. Their setup and usage are not covered in this course because additional information is required to configure these units. Full details can be found in the NAVION i2 User Manual and the DS_IMU_GYRO Manual.

NMEA compatible GNSS receivers

DewesoftX supports any GNSS receiver that transmits NMEA messages through a USB COM port. To add an NMEA-compatible GNSS receiver to the current device configuration, select the NMEA-compatible GPS option in the Add Device menu.

Similar to the Dewesoft RS232 GNSS receiver, the NMEA receiver is added to the current device configuration. If the device cannot be found, it is possible that the selected COM port is not the correct one. An Auto Search can be performed across different COM ports to locate the connected GNSS receiver. The COM port number of the connected receiver can also be found in the Windows Device Manager.

Legacy devices

In older DewesoftX releases, legacy devices could be found in the Hardware Settings. To add a legacy device, select the Legacy Devices menu in the Add Device window.

Legacy device support was removed from DewesoftX starting with the 2021.4 release.

First, you need to perform a quick Channel Setup where the required GPS channels can be defined and enabled for measurement. Next, create a proper display with the data you want to visualize. Once this is done, the measurement is ready to start.

Channel setup

When a GNSS device is added to the list of devices, a new GNSS screen appears in the DewesoftX Channel Setup.

The GPS screen in Channel Setup consists of:

• GNSS channel list – displays all channels available on the connected GNSS receiver.

• Status indicators:

  • Synchronization indicator – turns green when a PPS synchronization signal is received by DewesoftX.

  • GNSS fix status indicator – shows the GNSS solution type. In Image 32, the GNSS receiver is in standalone mode and colored grey. The indicator turns green when the status is RTK Fixed.

• Satellites in view – displays the satellites detected by the GNSS receiver. Satellites used in position calculation are labeled Used and color-coded according to their constellation (GPS – green, GLONASS – red). Satellites that are visible but not used in the calculation are shown in white.

Measure mode

In both Measure and Analysis modes, you can select different display types depending on your needs—such as recorder views, digital displays, etc. The Map Display shows GNSS data and visualizes the path recorded by the receiver, as illustrated in Image 33.

The Map Display is fully customizable in Design Mode, where it can be previewed in 2D, 3D, or Terrain View. These options can be selected under the Map Display Settings by clicking on the display; the corresponding settings will then appear in the left-hand window (see image below).

If synchronization is enabled, the current time will also be displayed in Measure Mode at the top of the screen, next to the computer resource status (see Image 33). Synchronization is successful when the circle turns green and the time is shown in black.

If synchronization is lost, or if there is a drift in the synchronization signal, the indicator light and the time display will turn red. Significant changes in the synchronization signal during data acquisition can trigger the creation of a new data file, which will then be synchronized according to the updated signal. This situation may occur after long periods without a valid GNSS fix.