Common Plots

Plots the standard deviation of the east, north and up directions as well as a 3D (labeled trace) value.

This plot is a good summary of other factors in your survey, including the float/fixed ambiguity status and satellite geometry. This is because SD values of fixed solutions are generally much lower than float solutions, and spikes in DOP caused by loss of satellite signals are typically correlated with spikes in estimated position accuracy. Please note that the estimated error plot contains no knowledge of any systematic error (such as biased base station coordinates or incorrectly fixed integer ambiguities), and as such the values reported are only (by definition) estimates.

This plot shows the standard deviation computed in the GNSS/INS Kalman filter in terms of roll, pitch and heading.

Plots the RMS of the double differenced C/A residuals for all satellites used in the solution. High C/A residuals often indicate high multipath.

Also plotted is the standard deviation applied to the C/A measurements within the Kalman Filter. This value comes in part by the a priori value set in the Measurement tab. In dual frequency carrier phase processing, where ARTK is used to resolve integer carrier phase ambiguities, the C/A code does not heavily influence solution accuracy. Thus the standard deviation assigned to the measurements is not important, provided it is not overly optimistic.

Adjusting the C/A measurement standard to a value more representative of the size of the actual residuals (while still being conservative) will benefit float solution convergence.

Plots the RMS of the double differenced carrier phase residuals for all satellites used in the solution.

Carrier phase noise increases as the baseline length grows due to factors such as residual ionospheric and tropospheric error. Further, if ionospheric processing is used, the carrier phase noise will increase noticeably (although it should still be cm level). Thus, while values at or below 1 cm may be typical for short baselines (1-2 km), values of 2-4 cm are typical for longer baselines (10-40+ km).

If large differences are found in the Combined Separation (fixed) plot, the RMS of the carrier phase can be a very helpful plot in determining which direction (forward or reverse) resolved the carrier phase integers incorrectly. When doing this, ensure to load each solution (forward and reverse) separately prior to plotting the carrier phase RMS, in order to ensure you are viewing the carrier phase residuals for each direction separately. Large ramping trends are strong indications of incorrect ambiguities.

Plots the RMS of the double differenced Doppler residuals for all satellites in the solution. Inertial Explorer uses Doppler to compute instantaneous velocity.

Also plotted is the measurement weighting applied to the Doppler measurements within the Kalman filter. As the quality of the Doppler measurements varies very significantly between receiver manufacturers, Inertial Explorer applies a somewhat conservative default measurement weight. Therefore it is common to see that the actual Doppler residuals are much lower (better) than the weight applied in our filter, although the opposite is also sometimes true depending on receiver type. A discrepancy between the actual magnitude of the Doppler residuals and the a priori measurement weighting will lead to an inappropriately high (or low) estimation of GNSS velocity.

Some receivers output such noisy Doppler values (on the order of 5 m/s) that it will actually cause Kalman Filter resets, significantly degrading positioning accuracy. Thus if you see very large residuals in this plot, we recommend disabling Doppler from the Measurement tab of the GNSS processing options.

This plot launches a dialog that provides access to cycle slip plots for all GPB files within the project, or a user defined GPB file.

Each satellite in the GPB file is plotted as a function of time and is color coded by elevation. See the bottom of the plot for a legend. Cycle slips for individual satellites are represented as a vertical red tick mark on the plot.

It is normal for cycle slips to occur on low elevation satellites (< 10 degrees) due to signal blockages or due to attenuation by the GNSS antenna.

Cycle slips on high elevation satellites may be expected if surveying in a challenging GNSS signal environment and are thus not necessarily an indication of a problem. However, if the plot shows many cycle slips on L1 or L2 in aerial survey applications where good signal tracking is expected, it can help diagnose receiver or antenna problems that can significantly limit post-processing performance.

If you are getting poorer than expected post-processing performance, checking the quality of L1 and L2 signal tracking at the remote and base stations is a good first step in determining the cause.

Provides access to satellite code residuals, phase residuals, elevation angles and C/NO values for individual PRNs.

Use this plot to see the raw gyroscope and accelerometer measurements as they appear in the IMR file.

Plots the north, east and height position difference between any two solutions loaded into the project. This is most often the forward and reverse processing results, unless other solutions have been loaded from the Combine Two Solutions dialog.

Plotting the difference between forward and reverse solutions can be an effective QC tool. When processing both directions, no information is shared between forward and reverse processing. Thus both directions are processed independently.

When forward and reverse solutions agree closely, it helps provide confidence in the solution. To a lesser extent, this plot can also help gauge solution accuracy. However, if there is a common bias in both forward and reverse solutions (for example, due to inaccurate base station coordinates or due to a large residual tropospheric error), it will never be seen in the combined separation plot.

Large differences in the combined separation plot may be a result of different solution types (fixed/float) or different levels of float solution convergence between the processing directions and thus not a direct indication of a problem. It is important to also consider solution status (fixed/float) when evaluating forward/reverse differences. This is why the Combined Separation with Fixed Ambiguity plot can sometimes be more helpful.

Similar to the Combined Separation plot, however only the position differences between forward and reverse processing are plotted where both solutions have fixed integer ambiguities.

Fixed integer solutions are associated with high accuracies (cm, or cm-level accuracies depending on other factors). Knowing this, there is an expectation of cm level differences between forward and reverse fixed integer solutions. If large differences (decimeter or meter level) are obtained, an incorrect ambiguity was very likely obtained in one or both directions.

In this event, loading each solution into the project individually and plotting the RMS - Carrier Phase can be useful in determining which processing direction the problem occurred. See the description for the RMS - Carrier Phase plot for more information.

This plot shows the difference between the forward and reverse solutions in terms of roll, pitch and heading. A zero separation is ideal, as it indicates matching solutions in the forward and reverse IMU processing. Spikes at the beginning and the end of the plot are common, as they indicate the periods of alignment.

PDOP is a unitless number which indicates how favorable the satellite geometry is to 3D positioning accuracy. A strong satellite geometry, where the PDOP is low, occurs when satellites are well distributed in each direction (north, south, east and west) as well as directly overhead.

Values in the range of 1-2 indicate very good satellite geometry, 2-3 are adequate in the sense that they do not generally, by themselves, limit positioning accuracy. Values between 3-4 are considered marginal and values approaching or exceeding 5 are considered poor.

If PDOP is poor in your survey, try reprocessing with a lower elevation mask (however care should be taken when lowering this value below 10 degrees).

This plot indicates where the processed solution is fixed (in one or both directions) or float. If both forward and reverse solutions achieved a fix, the plot shows a value of 2 and is plotted in bright green. If either the forward or reverse achieved a fix, but not both, a value of 1 is plotted. The value will be plotted cyan if the fixed direction is forward and blue if the fixed direction is reverse. If neither direction achieved a fix, a value of 0 is plotted which appears red on the plot.

This plot can be helpful to view in conjunction with the Combined Separation plot, as it will help determine if large values in the forward/ reverse separation are expected or not, depending on solution status in each direction. That said, the Combined Separation with Fixed Ambiguity plot is recommended to quickly check for the presence of incorrect ambiguity fixes.

Plots the number of satellites used in the solution as a function of time. The bar plot displays the total number of satellites (GPS, GLONASS, BeiDou, Galileo and QZSS). It does not distinguish between how many satellites are tracked from each constellation.

Plots the number of satellites used in the solution as a function of time. The number of GPS satellites, GLONASS satellites, BeiDou satellites, Galileo satellites, QZSS satellites and the total number of satellites are distinguished with separate lines.

Plots the coverage of each GPB file in the project, or a user specified GPB file, as a function of time. This plot indicates whether the data has been converted as static or kinematic (by different color codes) and shows the presence of any detected complete losses of carrier phase lock by vertical bars.

This plot is useful in determining whether any base station data does not overlap with the time range collected by the remote receiver.

This plot shows the distance between the master and remote. For multi-base distance separation, see Plot Multi-Base.

Plots the ellipsoidal height of the remote as a function of time.

Plots the north, east and up velocity. Also plots the horizontal speed.

This is the apparent output in acceleration when there is no input acceleration present. It is computed by the GNSS/INS Kalman filter and the effects may be sinusoidal or random. It is plotted in terms of the X (right direction), Y (forward direction), and Z (up direction) of the vehicle body. Generally, they should stabilize after the alignment period and agree when processed in both directions.

Plots the heading and GNSS COG (course-over-ground) that was computed from the GNSS/INS processing. Effects of a crab angle is visible in this plot if the GNSS COG bears a constant offset from INS heading. The IMU Heading COG Difference plot shows the difference between these two heading values. Note that any transitions between a heading of 359 degrees and 0 degrees shows up as a vertical line.

Plots the roll and pitch values from GNSS/INS processing. In airborne data, it is common to see roll values between 30 degrees and pitch values of around 10 degrees, depending on the flight pattern of the aircraft itself.

This plot shows the components of acceleration in the vehicle body frame.

Not available in Inertial Explorer Xpress.

This plot shows the components of velocity in the vehicle body frame.

Not available in Inertial Explorer Xpress.

This plot presents the DMI scale factor, as computed by the Kalman filter. It should be loaded separately for forward and reverse processing to ensure that the same scale factor is computed in both directions. Ideally, the plotted line should be horizontal, indicating a constant scale factor.

Not available in Inertial Explorer Xpress.

This plot presents the difference between the computed displacement or velocity and that reported by the DMI.

Not available in Inertial Explorer Xpress.

This tool allows DMI users to view the raw data measurements found in their DMR file. They can use the options available here to find an appropriate scale factor that will make the DMI data fit best with the values computed from the GNSS-IMU data.

Not available in Inertial Explorer Xpress.

This plot shows the estimated standard deviation of the accelerometer bias. It is plotted in terms of the X (right direction), Y (forward direction), and Z (up direction) of the INS body.

Not available in Inertial Explorer Xpress.

This plot shows the estimated standard deviation of the gyro drift rate, which generally decreases with time. It is plotted in terms of the X (right direction), Y (forward direction), and Z (up direction) of the INS body.

Not available in Inertial Explorer Xpress.

This is the apparent change in angular rate over a period of time, as computed by the GNSS/INS Kalman filter. The effects are usually random. It is plotted in terms of the X (right direction), Y (forward direction), and Z (up direction) of the INS body. Generally, they should stabilize after the alignment period and agree when processed in both directions.

This plot shows the gyroscope rate of change of attitude in the X, Y and Z axes of the IMU body with the drift removed. This plot is used to check the gyros.

Shows the status of IMU processing. Specifically, this plot provides indication of the type of update, if any, being applied at each epoch.

This plot presents the body-frame components of the lever arm offset between the IMU and GNSS antenna. If the offset was manually entered, then this plot has constant horizontal lines. If left to be solved by the Kalman filter, this plot shows the computed values.

This plot is the difference between the IMU heading and the GNSS course-over-ground values. Effects of crabbing shows up as a direct bias in this plot.

Not available in Inertial Explorer Xpress.

Plots the difference between the East, North and Up components of velocity computed during forward and reverse processing. Requires that both directions be processed and combined.

Not available in Inertial Explorer Xpress.