Introduction: Post Processing With a GeoExplorer3 GPS

Collecting features with any Global Positioning System (GPS) unit can be beneficial and interesting. Most people encounter GPS units after all the data collecting and processing is complete. We are here to show you the initial stages of collecting navigation points, of course, on a much smaller scale.  The Trimble GPS unit that we used for this project is the GeoExplorer 3.This hand-held GPS unit can receive and collect data for relocation, mapping, and other data collecting with multiple navigation screens.

The two programs we used for this project were:

1. Pathfinder Office , a software program designed for data exporting/importing, mission planning, post processing, and other data analysis.

2. ArcGIS, a program designed to create layers that allow you to distinguish between the correct points and the actual points.

Note: For these specific instructions, we used these two programs because we had the most experience with them. These instructions may not work the same for other programs. If you do use these programs, we do hope our instructions are efficient and effective.

The following instructions are to aid you in transmitting your collected data as well as post-processing all or your files in Pathfinder Office and ArcGIS. We hope our instructions help you out in the best ways possible. Good Luck!

Step 1: Transmitting Collected Data Instructions: Steps 1-2

The following steps will assist you in uploading your data to a computer once you have collected your desired points using a GeoExplorer3 GPS unit.

1. Place the GeoExplorer3 GPS unit, containing your collected data, into the module cradle.

2. Connect the cradle to the back of your computer.
  
Note: The GeoExplorer3 uses a COM1 PORT, but other units may use a USB drive. Consult your user guide for the proper PORT.


Step 2: Transmitting Collected Data Instructions: Steps 3-6

3. Open up Pathfinder Office and after all connections have been made, pull down the "Utilities" menu and select "Data Transfer".

4. Make sure the receiver tab is selected on the "Data Transfer" window and click the "Add" button and select your file.

5. Once you have highlighted the file or files that you want transferred, click "Open". The files you have selected will appear in the "Data Transfer" window.

6. When all files are displayed in the window, click the "Transfer All" button. This will transfer all the selected files to Pathfinder Office .

Step 3: Transmitting Collected Data Instructions: Steps 7-9

7. With Pathfinder Office open, pull down the "View" menu and select "Map". This will open "Map View".

8. With the "Map View" open, pull down the "File" menu and select "Open" and navigate to your file(s) you want opened.

9. The locations will appear inside the "Map View" window. If needed, re-size the window by going to the "Data" menu and selecting "Feature Properties".

Once this is complete, continue to follow the instructions to assist in post-processing your points.

Step 4: Post-Processing Your Positions

Post processing is taking positions you have collected and correcting them with data that has previously been collected and processed for more accurate results. This will provide more accurate locations because it will account for errors such as satellite interference (Ephemeris data, Clock Drift, Selective Availability), atmospheric errors (Ionosphere, Troposphere), and receiver errors (receiver noise, multipath). These errors could affect the overall accuracy of your locations anywhere up to 30 meters in all directions. So this program is very vital to your data and navigation. After all data has been collected you are ready to move on to the post-processing of the data. To help you with the post-processing of your data, follow these step-by-step instructions we have provided for you.

Open Pathfinder Office , click on the "File" menu and select "Open". Open your file that contains your data.

After the file has been opened, your uncorrected data will show up in the "Map View" screen, as seen in the image.

Step 5: Post-Processing Your Positions

Go to the “Options” menu and choose “Coordinate System” and choose the correct coordinates.

Step 6: Post-Processing Your Positions

In the "Coordinate System", check to make sure all appropriate tabs are checked.

• "Coordinate System" and "Zone"
• "System" is set to Latitude and Longitude.
• "Datum" is set to NAD 1983 Conus.
• "Altitude" is set to Mean Sea Level.
• "Units" are set to Meters.

Click “OK”.

Step 7: Post-Processing Your Positions

Navigate to the “Utilities” menu and choose the “Differential Correction”.

Step 8: Post-Processing Your Positions

Your file should be in the "Select SSF" window.

Note: If your file is not displayed in the window select the "+" sign and select your file from your storage device.

Click "Next".

Step 9: Post-Processing Your Positions

Check to make sure the "Automatic Carrier" and "Code Processing" tabs are selected.


Click "Next".

Step 10: Post-Processing Your Positions

Nothing has to be changed or added to this screen, simply hit the "Next" button.

Step 11: Post-Processing Your Positions

Next, you will need to find the appropriate base station so your files can be post-processed. You will want to use the closest base station to your location. Pathfinder Office (PFO) makes all this very simple. To do this first select the "File" menu and click the “Select”button and select your closest base station. Click "Next".

Step 12: Post-Processing Your Positions

Make sure that the “Use the Project Folder” is correctly marked in the "Output" folder as well as the “Create a Unique File name Based on the Input File Name” is correctly marked. Click on the “Start” button.

Step 13: Post-Processing Your Positions

This screen shows that your closest base station has been selected. Click on the “Confirm” button to continue.

Step 14: Post-Processing Your Positions

Select the “+” button located on the top left part of the window. The "Add Data" window will be displayed.

Step 15: Post-Processing Your Positions

Navigate to your storage device and select your file where your data is located.

Step 16: Post-Processing Your Positions

Select and hit "Add" to all files you would like to display. Your files will appear in the left column labeled “Layers”.

Step 17: Post-Processing Your Positions

When all steps are done correctly all your actual and corrected positions will show in the "Map View" window.

Note: Make sure that your boxes in the “Layers” column are checked. This will allow you to view them.
       
      Red: Corrected positions
      Green: Actual positions


Although the post processing program improves your accuracy, it is in no way perfect, as indicated by our example. From the data that we have collected you can see that we had some type of interference, possibly multipath interference, that affected the accuracy of our locations. This is shown by the fact that the red and green points have deviated from each other. Overall, the actual distance to the uncorrected distance would be greater if not post processed.

We hope these instructions were clear, effective, and useful to you. Thank you!

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