Chapter 6
Pathfinder Office Part Two

Data Transfer and Manipulation  

            In this section, you will learn a variety of useful techniques for manipulating data after it has been transferred from the GPS receiver. You will learn how to combine files (if you had to log data on different occasions), how to differentially correct the GPS measurements taken previously and exporting the data for use in GIS applications. This section will focus on using Pathfinder Office 2.90, which has to be used with the Geoexplorer for its Super Differential Correction function, which, in short, means a much-improved level of accuracy.

Transfer Data 

   Follow the instruction in the previous sections, depending on which unit you used, to connect the GPS unit to a computer and transfer files. Remember to make a note of where you transferred the files.

Combining Files 

   This technique becomes necessary if you took measurements from the same area more than one week apart. Trimble receivers will normally not add new data to a file if it hasn’t been transferred within a week of recording. To overcome this problem, the Pathfinder Office software is equipped with a combine function in the Utilities menu, or as a button on the sidebar (to find, simply allow you mouse to sit on top of the buttons to the right of the main work area hint: try the fourth button from the bottom).

    After selecting the combine feature, you will see a small dialogue box that allows you to select those files that you wish to combine into a single file.

    The first step is to use the Browse button to select the files, you can then select the Output File’s (that’s the new file you will create which will contain all the data in the individual files) location and name by selecting that button. Sorting is not to important, so just stick with Chronologically.

   Once you have selected the names and locations of your Input and Output Files, you can hit the OK button, and Pathfinder Office combines all the data into one file.

   Combining files is the best way to work with a large amount of data, doing so before any of the other operation in this section is highly recommended to allow you to cut down on time and resources later.

Differentially Correcting GPS Data 

   The first step is to start Pathfinder Office, open the file where your GPS data is stored. Then, to enter the Differential Correction dialogue, simply select it from the buttons to the right of the work area or below the Utilities menu.

   As you may remember from the DGPS chapter, to differentially correct a file, you need to have two files, the receiver (Rover) file(s) and base station file(s).

   When you start the Differential Correction dialogue, it will automatically select the current file open in Pathfinder Office. However, if the file is not listed below the Rover Files section (under Selected Files) or you want to add files, simply use the Browse button to locate them and select Add.

There are three ways in which you can find and use Base Station data.

·        Local Search – this allows you to search for Base Files already saved to you computer or network (as may happen if you were operating a Base Station in the field, however this function goes above the scope of this manual).

·        Internet Search – you can set up the Pathfinder Office software to automatically access and select files over a network.

·        Browse – allows you to select specific files from your computer to use as Base Files (similar to Local Search).

The University of Otago has an agreement with gpscontrol.com for use concerning the Base Station data collected by the Department of Surveying. The Base Station at Surveying can be used for data collected throughout most of Otago and parts of Southland. However, the relevance of the base data drops as you move farther away from the Base Station, and most of Otago and Southland can safely be mapped and corrected using this Base Station.

Please see Appendix A “Sources of Data in Otago” for more information on how to set up an Internet Search using the Base Station data from Surveying.

  Now, after having selected the Rover and Base files, you can select OK, but before doing that, you should take a look at the Settings. These settings allow you to take full advantage of all that the Differential Correction function offers. 

    The following Photos illustrate a standard arrangement of settings, and should be followed (change the current settings if they are different) to allow for maximum effectiveness.

Once you have made those Settings changes, you can select OK, and you are ready to differentially correct you data. Also, at the main Differential Correction menu, make sure that Smart Code and Carrier Phase Processing is selected under Processing, then simply select OK from the Differential Correction dialogue box, and let the computer process the files.

 

Now that your files are corrected, you have increased the level of accuracy substantially. While there is no way to create a standard level to represent how much accuracy has increased, there are approximations. For the Pro-XR unit, which recorded positions accurate to within a meter or two, the accuracy after differential correction is now within one meter. For Geoexplorer, which already has an accuracy of less than one meter, its increased accuracy is possibly on the order of 10 cm or less.

Exporting Files

   You might want to export files for a variety of reasons, the most common reason is for use in a GIS environment (such as MapInfo or ArcGIS). The main trick to making sure that files transfer correctly is to get the right mix of settings before you actually export the files. These settings are the focus of this section. 

   The majority of settings for each file type are the same, however, making changes to the settings of one type of file (such as a shapefile for use with ArcGIS) will not affect the settings for another type of file (say a MapInfo document). Actually, each type of file does have one section in its settings dialogue box that is specific to that type, but individual file type settings will not be discussed here. It is assumed that if you know enough to export to a file type, then you have some experience using that software. Therefore, every time you wish to export to a new file format, you must change the settings. Also, do not assume that whomever used the application before (if working on a shared access machine) new what they were doing, CHECK THE SETTINGS. Possible problems that may result from incorrect settings include inaccurate positions settings or no positions at all.

    To begin, start the Export dialogue box from the Utilities menu or from the button at the right of the work area.

   Use the Browse button in the Input Files section to add files you wish to export, you may select more than one.

   Choose the Output Folder (files will be named the same in the output folder as the Input File name). Choose an Export Setup type, and then you are ready to change the settings on that specific Export Setup.

    Again, we will look at a series of screenshots from the software to quickly illustrate the correct settings for making sure that files correctly export to your chosen format. Notes will be added between photos for clarification (as needed).

    The attributes can be changed to anything you like, all this does is add field to the exported data that will record the type of data listed into tabular form. Meters is a universally standard Units settings, and selecting Use Export Units helps to standardize your data.

    Use Current Display Coordinate System allows you to avoid some potentially precision destroying position accuracy, and selecting XYZ allows you to take advantage of the 3D aspect of GPS (the altitude accuracy of GPS receivers is increasing along with the horizontal accuracy, but is not as accurate).

   The final screen in Settings allows you to make changes to the type of file itself, as you can see above, the ArcView Shapefile format was selected, and to make changes to this file type, you should have a working knowledge of the software you wanting to export data to. However, most of the standard defaults in this last menu folder are suitable and are probably able to be left alone (especially since most of them are extra features that aren’t required, such as adding a Shapefil Tracking Theme).

   Select OK, and you are back at the Export menu, simply select OK here and the computer will create the new files to the Output Folder that you specified, be sure to remember where you stored the files.

Closing Comments 

            Pathfinder Office allows you to edit the position data, it even allows you to create new features (look under Data/Create Feature). You can even display aerial photos below your position data, however you must georeference the photo using a GIS program. In short, the Pathfinder Office software lets you work with you data in a number of ways, it may be interesting to ask for the user’s manual from whomever provided the GPS units themselves. However, everything you need to know about basic GPS data collection has been covered in this manual, and the skills developed here will allow the most novice users to take advantage of this rapidly growing technology.

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