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GrafNav

Chapter 2

 

 

 

2.7 Output Menu

X -Axis (Time)...

Select X-Range

Previously used settings of the X-axis are stored here.

Apply to All

Scales the X axis of the other opened plots to facilitate analysis.

Auto-scale

Shows the entire time range of the data.

Set Minimum

Makes the current time the X-axis minimum.

Set Maximum

Makes the current time the X-axis maximum.

Y-Axis (Value)...

Select Y-Range

Previously used settings of the time range are stored here.

Apply to All

Scales the Y axis of the other opened plots to facilitate analysis.

In order to apply the Y axis to all plots, the maximum and minimum values must be manually specified, that is, not auto-scaled.

Auto-scale

Shows the entire value range of the data.

Set Minimum

Makes the current time the X-axis minimum.

Set Maximum

Makes the current value the Y-axis maximum.

2.7.1 Plot GPS Data

This feature is very useful for analyzing GPS data and processed results. The plots are divided into eight groups, and the Build Custom List button allows you to form their own list of plots that will show up under the Custom group.

Along with selecting the plot type, you can define X-Axis and Y-Axis information. Changes made to these pages are retained for future plots. For example, if a time range is entered in the X-Axis, the same time range is used for future plots in this project. This is very useful for inspecting a narrow time slice. You can still make changes to axes information after the plot has been displayed by right-clicking on the plot.

If features are loaded, then there are vertical red bars along the top of the plot. Click on the feature to show solution status information.

Add Group

Defines a set of plots for easy viewing access. Once a group has been created, it appears under the Grouped Plots branch on the main window. This facilitates the task of opening plots for those users who are continually analyzing the same ones after every run of processing. Any userdefined group of plots can also be automatically opened after completion of processing via

Settings | Preferences. See Section 2.6.10, on Page 102 .

The following plot features are available by rightclicking on the plots:

Properties

Allows access to many settings, like X and Y axes ranges and the display format for the latter. The plot titles, along with the X and Y axes labels, can all be edited here. Other options regarding the displaying of camera marks and the usage of thick plotting lines are available too.

X -Axis (Time)...

The option are listed in the shaded box.

Y-Axis (Value)...

The option are listed in the shaded box.

Copy

Copies the plot onto the clipboard as a bitmap (BMP), allowing you to paste the image into other application such as MS Word or Paint.

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Copy (without title)

Copies the plot onto the clipboard as a bitmap (BMP) without the plot title.

Save to HTML

Copies a BMP version of the plot into an HTML file, which opens upon completion. The HTML and BMP files are saved to the project folder under a directory called HTML.

Refresh

Reloads the selected plot.

Go to Time…

Gives you the option of finding the nearest available time in the forward or reverse message logs, or finding the nearest epoch on the Map Window.

Compute Statistics for…

Calculates many useful statistics for either the entire valid processed time range, or, if it has been adjusted, only the time range being plotted. Statistics include RMS, average, maximum and minimum. Note that this feature is only available for appropriate plots.

Set Start Processing Time

Makes the selected time the start time for processing.

Set End Processing Time

Makes the selected time the end time for processing.

Engage KAR/ARTK at Time

Engages KAR at the selected time.

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Chapter 2

 

 

 

Common Plots

Table 4 contains a list of common plots that are available through the Plot GPS window.

Table 4: Common Plots

 

 

Plot

Description

 

 

Accuracy

 

 

 

 

Plots the standard deviations of the east, north and up

Estimated Position

directions versus time for the solution. The total

standard deviation with a distance dependent

Accuracy

component is also plotted. View this plot for individual

 

forward or reverse solutions and losses of lock.

 

 

 

Velocity is the local level component (easting, northing,

 

up) computed by the Kalman filter. These are mostly

Estimated Velocity

derived from the Doppler measurements. Plotting the

Doppler RMS is a good way to check the actual

Accuracy

accuracy based on real data. Plotting the estimated

 

standard deviation shows the theoretical accuracy

 

based on the Kalman filter error estimates.

 

 

Measurement

 

 

 

 

Plots the root mean square combination of the code

RMS – C/A Code

residuals. This is a good indicator of receiver code

measurement accuracy and of multi-path for carrier

 

phase processing. Large jumps can be induced by

 

missed carrier phase cycle slips.

 

 

 

Plots the root mean square of the L1 phase or L1/L2

 

iono-free phase combination residuals. This is a good

 

indicator of carrier phase measurement accuracy. If the

RMS – Carrier Phase

signal is affected by the ionosphere and other error

sources, the RMS will be greater than the few

 

centimeter range and can be as large as 10 cm or more

 

for single frequency. Since the code and carrier phase

 

are combined, some noise from the C/A code can seep

 

into the carrier phase.

 

 

 

The Doppler is used for velocity determination. When

RMS-L1 Doppler

using GrafNav in conjunction with inertial (INS)

integration, pay close attention to this plot. It gives a

 

good indication of what standard deviation to give

 

velocity data in the inertial Kalman filter.

 

 

RMS-P Code

If the option Use P-Code in Kalman Filter is enabled,

then this feature can be used to plot the P-Code RMS.

 

See Ionosphere/L2 Options on Page 79 for information.

 

 

 

Use this plot to view the quality of the data contained in

 

a GPB file. The plot shows four data characteristics

 

including the following:

 

• The cycle slips in the data for each satellite,

 

indicated by vertical bars. This information is

 

useful for detecting poor tracking.

 

• The available time range for each satellite in the

 

GPB file.

Satellite Lock – Cycle Slips

• The third characteristic shown is the elevation

 

angle for each of the satellites. The different

 

colours represent different elevation ranges.

 

• The final characteristic shown is data that will not

 

be used for processing as the options stand,

 

shown in red. This means that either the C/A

 

range or phase data (L1 or L2) is invalid, or the

 

locktime of the satellite is less than the locktime

 

cut-off. Black lines indicate missing ephemerides.

 

 

Individual Satellite

Shows satellite code residuals, phase residuals,

Statistics

elevation angles and C/NO values for individual PRNs.

 

 

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Table 4: Common Plots cont.

 

 

 

 

 

Plot

Description

 

 

 

 

 

 

Separation

 

 

 

 

 

 

 

 

Requires forward and reverse solutions to be combined

 

 

 

and displays the difference between the two

 

 

Combined Separation

trajectories. For multi-baseline combination in GrafNav

 

 

Batch, this is the maximum minus minimum difference

 

 

 

between baselines for each epoch and the number will

 

 

 

always be positive.

 

 

 

 

 

 

Combined Number of

Shows the number of baselines that are used to form a

 

 

combined baseline. This is useful for multi-base

 

 

Solutions

 

 

processing.

 

 

 

 

 

 

 

 

 

 

This plot applies to multi-base batch mode processing.

 

 

 

Instead of showing maximum minus minimum like the

 

 

Combined RMS

Combined Separation plot does, it shows the weighted

 

 

RMS of the baseline. Thus, if one baseline does not fit

 

 

 

well, but it is given a very low weighting, it will not affect

 

 

 

this plot as much. It is a good idea to view both because

 

 

 

this plot can be optimistic.

 

 

 

 

 

 

Quality Control

 

 

 

 

 

 

 

 

Indicates satellite geometry relating to position. Small

 

 

 

values indicate better geometry. Lines are displayed for

 

 

DOP – PDOP,HDOP, VDOP

position DOP (PDOP), horizontal position DOP (HDOP)

 

 

and vertical position DOP (VDOP). These values should

 

 

 

be similar to other PDOP computations, but differences

 

 

 

can be visible due to different base satellite selection

 

 

 

(double differencing).

 

 

 

 

 

 

 

Indicates satellite geometry relating to position. Small

 

 

 

values indicate better geometry. This value is the

 

 

DOP-DD_DOP

double difference DOP and is approximately PDOP, it

 

 

can be lowered due to the differential modeling. The

 

 

 

DD_DOP is used for all internal checks and DOP

 

 

 

related options in the software. Epochs with extremely

 

 

 

poor DD_DOP (>100) are skipped and are not plotted.

 

 

 

 

 

 

 

This plot shows whether an epoch has a fixed or float

 

 

Float/Fixed Ambiguity Status

ambiguity status. Fixed integer ambiguities generally

 

 

have better accuracies. This plot also shows if there are

 

 

 

zero, one or more fixed ambiguities used to determine a

 

 

 

combined solution.

 

 

 

 

 

 

 

Number of satellites for epochs. This plot gives an

 

 

Number of Satellites (BAR)

overview of how many satellites there are. Use this

 

 

graph for large data sets because it shows every time

 

 

 

the number of satellites drops to a minimum. Epochs

 

 

 

with less than 4 satellites are not displayed.

 

 

 

 

 

 

 

This plot shows the number of GPS, GLONASS and

 

 

Number of Satellites (LINE)

total satellites. Epochs with less than 4 satellites are not

 

 

displayed. This plot contains more information than the

 

 

 

bar plot.

 

 

 

 

 

 

 

This plot shows if and when GPB files are static and

 

 

 

kinematic. It can overlay multiple GPB files to see if they

 

 

 

overlap in time and to indicate weak periods of the data

 

 

File Data Coverage

that could result in a loss of lock. Since it does not

 

 

examine processed data, this plot is not as reliable as

 

 

 

other indicators. If you have Inertial Explorer, you can

 

 

 

plot IMU coverage and use this plot to show IMU data

 

 

 

time gaps.

 

 

 

 

 

 

 

This value indicates solution stability for a float solution.

 

 

 

The ambiguities should be driftless and have a drift of 0

 

 

Ambiguity drift

cycles/sec. Normally, this number will be 0-0.03 cycles

 

 

for very stable solutions, and 0.03-0.05 for quality 2

 

 

 

stability, and so on for Q3 and up. Most users rely on the

 

 

 

quality number instead of this plot. The quality number

 

 

 

is partially derived from this parameter.

 

 

 

 

 

Continued on the following page.

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Chapter 2

 

 

 

 

 

 

Table 4:Common Plots cont.

 

 

 

 

 

Plot

Description

 

 

 

 

 

 

 

 

Coordinate Values

 

 

 

 

 

 

 

 

Distance Separation

This plot shows the distance between the master and

 

 

 

remote in kilometers. For multi-base distance

 

 

 

separation, See the multi-base plotting tools.

 

 

 

 

 

 

Height Profile

Height over the processing time period. This can be a

 

 

 

very good quality control measure in areas where the

 

 

 

height is very stable.

 

 

 

 

 

 

 

This plot assumes that the last epoch in the static

 

 

 

Static Session Convergence

session is the correct one. A float solution convergence

 

 

plot is then formed. This gives an indicator of how well

 

 

 

a static solution is stabilizing.

 

 

 

 

 

 

Velocity Profile

Plot shows north, east and up velocities, which can be

 

 

 

used to determine when the antenna is moving. This

 

 

 

plot also shows horizontal speed.

 

 

 

 

 

 

Acceleration Profile

This plot shows the approximate acceleration computed

 

 

 

by the baseline processor. For this plot to be shown,

 

 

 

enable the Extended trajectory output.

 

 

 

 

 

 

Height Above Ground

This plot is to be used in conjunction with a DEM to

 

 

 

display the remote’s height above the ground.

 

 

 

 

 

 

 

 

 

 

 

This is the vector between base and remote centered

 

 

 

Local Level Vector

about the main base station. It is useful for moving

 

 

baseline processing. For absolute positioning

 

 

 

applications, the distance separation combined with the

 

 

 

height profile is usually a better diagnostic tool.

 

 

 

 

 

 

 

Miscellaneous

 

 

 

 

 

 

 

 

Estimated Clock Accuracy

This plot shows the estimated standard deviation

 

 

 

computed by the least-squares single point processor.

 

 

 

In general, it matches position accuracies.

 

 

 

 

 

 

GPS/GLONASS Time Offset

The time offset shown here is the computed difference

 

 

 

between the GPS system time and the GLONASS

 

 

 

system time.

 

 

 

 

 

 

 

The single point processor computes a clock correction

 

 

 

Receiver Clock Offset

on an epoch-by-epoch basis. This value is the

 

 

difference between the receiver's clock and the GPS

 

 

 

time system. For some applications, you may wish to

 

 

 

plot and monitor this value.

 

 

 

 

 

 

 

This feature can be used to plot data from a comma or

 

 

 

User Selected File - Plot data

space separated file. This spares you from having to

 

 

use a program such as Microsoft Excel or MatLab to plot

 

 

 

from

 

 

the data. It can also be used to plot the results of the

 

 

 

Compare utility.

 

 

 

 

 

 

Tropospheric Bias Estimate

Plots the tropospheric correction value as determined

 

 

 

by the Kalman filter

 

 

 

 

 

 

 

 

 

 

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