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Chapter 5

GrafMov

 

 

5.1Overview of GrafMov

GrafMov is a moving baseline upgrade that can be added on to Waypoint’s GrafNav / GrafNet GPS postprocessing software package. GrafMov software is for relative processing between two moving GNSS antennas.

This optional processing module allows for relative position and velocity determination between two moving antennas. Accuracies can be much higher than those achieved when processing from a fixed base station because relative distances tend to be much shorter. If the two antennas are fixed on the same craft, a post-mission heading determination system is formed.

This chapter describes how to get started with GrafMov, goes through each menu of its interface and provides step-by-step instructions for first-time users.

5.2Getting Started with GrafMov

Before you start a project in GrafMov, verify installation and convert data. This section provides a quick tutorial on how to get started with GrafMov.

Install Software

Verify that the installation was successful by ensuring that you have a Waypoint GPS program group on your computer. If this program group is not there, see Section 1.2.2, on Page 24 for installation instructions.

Convert Data

To be processed, raw GPS data files have to be converted into Waypoint’s GPB format, including raw data from Waypoint’s data-logger program. Instructions on how to convert these files are in the shaded box.

The GPBView utility can be used to switch between static and kinematic mode. See Chapter 3 on Page 221 for a complete description of the Convert utility.

Create a New Project

The steps to create a new project are listed in the shaded box. The Auto Start feature can also be used to automatically bring up all the pertinent dialogue boxes. See Section 2.2, on Page 32 for more information on the Auto Start feature.

How to install software

1.See Section 1.2.2, on Page 24 for installation instructions.

How to convert data

1.Select File | Convert | Raw GPS to GPB to access the converter.

2.Navigate to the directory that contains the data.

3.Select Auto | Add All to auto-detect GPS formats.

4.If you want to change the conversion options, click on Options or Global Options to set the rover to kinematic mode.

How to create a new project

1.In GrafMov, select File | New Project |

File Name.

2.Enter the name of the new project.

3.Click Open.

Entering the name of a project that already exists overwrites the file contents.

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Chapter 5

GrafMov

 

 

How to load master file (s)

1.After creating a new project, the screen appears empty. Select File | Add Master GPB File(s).

2.Select one of the moving stations as the base station and click OK. The program will load the GPB file and then a dialogue box will appear asking for the appropriate master station coordinates

3.Click on the Datum Options button to select the processing datum.

4.Select the desired datum from the list in the Processing Datum box. Be sure that the radio button labeled Use processing datum by setting processing datum to local datum is selected. See

Section 9.10, on Page 285 for more information on datums. If the datum has changed, GrafMov will warn you.

How to load the remote file

1.Go to File | Add Remote GPS File to select the remote station and click OK.

2.Enter the height of the antenna or range pole (height of phase centre above ground) when you are prompted to enter the remote station antenna height.

3.Press OK.

How to process

1.Select Process | Process Differential.

2.Click on the Process button to begin postprocessing the GPS data.

3.For the Static Initialization mode, select Float for kinematic initialization or Fixed Static if there is a sufficiently long static period at the start.

4.Click on the Process button to begin postprocessing the GPS data.

How to export final coordinates

1.Select Output | Export Wizard. Select the source for the solution. Epochs will output the trajectory, while Features/Stations will export any loaded features

2.Choose a profile and select Next.

Load Master File(s)

The steps for loading master file (s) are in the shaded box. When loading master files, make sure that the data from both moving stations must have been logged simultaneously. When loading, remember that base station coordinates are irrelevant in because the base station is moving but try to enter the appropriate antenna information.

Load Remote File

The steps on how to load a remote file is in the shaded box.

Select Moving Baseline Options

To successfully process moving baseline data, go to

Settings | Moving Baseline Options. The Enable moving baseline processing options must be enabled. If you are interested in attitude determination, indicate so with the options under Azimuth Determination. See on Page 194 for more information on the options available.

Process

The steps for processing are in the shaded box. For this tutorial, the defaults associated with the software will be accepted. See Chapter 3 on Page 61 for more information.

While the program is processing, pay attention to the quality bar. Ideally, it should settle down to a level of 1 or 2 if the GPS data is reasonably good. See Section 2.7.12, on Page 127 for a description of the quality factor.

If this bar spikes, it will probably coincide with a loss of lock or large phase and pseudorange RMS values, and possibly unstable ambiguity numbers and corresponding solutions. For slower computers, view the values during processing but faster units process epochs at such a high speed that visual inspection is likely impossible. This should not cause concern since all statistics will be available upon processing completion.

Plotting and Quality Control

Select Output | Plot GPS Data. From the list of options, several plots can be viewed. See Table 4 on Page 107 for a description of these plots.

Export Final Coordinates

The steps for exporting coordinate files are in the shaded box. For the Select Output Coordinate Datum screen, using the processing datum is recommended. You might also be prompted for the geoid undulation file, which are provided on the distribution CD. Section 2.7.4, on Page 111 for help.

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