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GrafNav

Chapter 2

 

 

 

2.5.3Combine Solutions

Combine Diff. GNSS / PPP Forward and Reverse

This processing combines GrafNav solution files processed in forward and reverse mode to form an optimal solution using variance weighting.

The benefit of combining these solutions is that the overall accuracy is improved because in many cases, one direction is more accurate than the other for a given epoch. This accuracy difference may change during the mission but the weighting function should reflect these accuracy differences.

By combining the forward and reverse solutions, a difference can be computed and plotted. This difference graph, available via the Combined Separation plot under Output | Plot GPS Data, gives an indication of solution accuracy and problem areas. However, the actual accuracy is often better because the combining process places more weight on the solution with greater estimated accuracy.

Before this process can be executed, there must be a forward (FWD/FSP) and reverse (REV/RSP) solution file present. A weight between 0 and 100 is assigned to both the forward and reverse solutions. The sum of both equal 100. All three axes (latitude, longitude and height) are assigned the same weighting value. The weight is computed by (1 / variance). Fixed integer positions are weighted much stronger than float solutions.

This process combines trajectory data (for kinematic) and also static sessions if any exist. For static sessions, the best solution may be chosen.

Enable the Automatically write.CMB file when combining option under Settings | Preferences to automatically create a combined trajectory file (CMB/CSP).

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Chapter 2

GrafNav

 

 

How to create combined solutions

1.Export the combined solution for each project using Output | Write Combined (.CMB/CSP) File.

2.In the current GrafNav project, use Process |

Combine Solution | Combine Any Two Solutions.

3.Select the CMB/CSP files when prompted.

Any Two Solutions

This feature is similar to the Combine Diff. GNSS / PPP Forward and Reverse option, except that any two solutions can be combined. This option combines created solution files using different processing settings. This is helpful for examining the effect of changing the processing options. It also allows you to compare a fixed solution to a float solution to detect a bad ambiguity resolution.

While GrafNav Batch is preferable, you might want to use this feature. To do this, follow the steps in the shaded box.

In order for a combination to be valid, the solutions must be computed from data that was collected at the same time, using the same antennas and the same receivers.

Combine Settings

This feature rejects certain time intervals of the forward or reverse solution so that areas with bad results are not included into the combined solution.

Click on the Add button to enter the times to exclude the forward or reverse solution from the combination.

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GrafNav / GrafNet 8.10 User Guide Rev 4

GrafNav

Chapter 2

 

 

 

2.5.4Launch Batch Processor

This options loads and runs GrafNav Batch. See Chapter 4 on Page 179 for information on how to use GrafNav Batch.

2.5.5Stop Auto Run

If the software is running from the command line (auto-run mode), this selection stops the auto-run. Depending on the quit mode selected, pressing Stop in the processing window may return control to the calling application. This selection just breaks out of auto-run. Run GrafNav with the –h command for a help screen.

2.5.6Load GNSS Solution

This feature allows for the loading of GNSS solution files. Choosing Load Forward Solution or Load Reverse Solution automatically loads the solutions most recently processed in the chosen direction.

2.5.7Load PPP Solution

This feature allows for the loading of GNSS solution files. Choosing Load Forward Solution or Load Reverse Solution automatically loads the solutions most recently processed in the chosen direction. Load PPP Solution is only be available if the single point processor has been engaged. See Section 2.5.2, on Page 85 for more information on single point processing.

2.5.8Load Any Solution

This option allows you to load any solution file. This is useful if previously processed solution files have been saved to disk.

2.5.9Import Solutions and Setting

This feature does the following:

Reads all configuration file settings from the selected CFG

Copies the processing files associated with the CFG

Loads the new solution into memory

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