PostProcessing-Viewing and Editing Data in Pathfinder Office

Using directions from your previous exercise, transfer all files created during data collection from the last class. Today you will learn to enhance, modify, and manipulate GPS data.

A. Opening Files

You can open as many files together as you want if you just want to view them. Editing files requires that only a single file be opened.

  1. Use the icon to open your complete set of .ssf files.
  2. To view the files, select “View” from the main Pathfinder Office menu and then “Map” or click on the icon. The points, lines, and areas collected in the field should now be displayed as points, lines, and areas on a white window.
  3. Select ““View” from the main Pathfinder Office menu and then “Time Line.” or the icon. A temporal record of data collection will appear.

This information is useful to correlate observation with PDOP, how productive your workers are out in the field, and whether data straddles a two or one hour data collection session. Perform a screen capture of your timeline and include it with the questions asked at the conclusion of this handout. At what time were your points collected?

4. Experiment with the measure tool to determine distance between select points.

B. Configuring the Map Window

We’ll configure the map window so that everyone involved in this assignment will use symbols that are better representative of what is actually being portrayed.

  1. Select “View” from the main Pathfinder Office menu, “Layers,” and then “Features” A “Features Layer” window appears.
  2. From the “Features Layer” window select the equivalent point feature in your scheme and choose “Symbol.”
  3. A window appears with a host of possible symbols. Choose a symbol that better represents the point feature portrayed. Click “OK.” Select your own scheme for lines and areas.
4. Customize the line thickness and color for your line and area feature.
C. Viewing Attributes and Positions of a Feature

Attributes can be viewed and edited in Pathfinder Office. You can also delete positions that make up a feature if these positions are erroneous. REMEMBER, IF YOU HAVE MULTIPLE FILES OPEN YOU CAN VIEW BUT NOT EDIT OR DELETE POSITIONS.

  1. Click the select tool and in the map window double click any feature. A small “Feature Properties” window appears. Select different features by using the select tool or use the “First” <, >, and “Last” button to move to the first, previous, next, and last features respectively.
  2. Below “Attribute Name” in the window is a list of any the attributes and associated values for a particular feature (we haven’t assigned attributes yet). Select the Attribute tab and you can edit any value. If more than one file is open you will be unable to edit features. Click on the “68% precisions” tab in the “Feature Properties” window.
  3. Record the “horizontal” value achieved for any point feature.
  4. Record the “horizontal” value achieved for any line feature.
  5. Record the “horizontal” value achieved for any area feature.
  6. From the main Pathfinder menu click on the “Positions Property” button to access further information about any feature like UTM coordinate location, altitude, and DOP values.
  7. You are now ready to delete any widely curving positions that give your area feature a “zig zag” appearance. Click on the erroneous position with the select tool; click the right mouse button and a small window appears. Choose “Delete Position” NOT “Delete” or the entire line will be deleted. Continue to edit lines until a reasonable representation of surveyed features appears. After editing area and line features:
  8. Using information from the “Summary” tab on the “Feature Property” window, find the total amount of area in m2 for your area feature.
  9. Using information from the “Summary” tab on the “Feature Property” window, find the total length of both line features in m.

D. Opening a Background File

Pathfinder Office allows background files, like digital raster graphics (DRG) and aerial photographs available for free at various governmental agencies, to be opened within the map window. While vector files can be loaded and transferred into any coordinate system “on the fly” by Pathfinder Office, raster files (like the Mt. Pleasant DRG used in this project) must be displayed in the same coordinate system, datum, and geoid as the differentially corrected files in Pathfinder Office.

1. We collected our data with the WGS 84 datum. To allow a DRG register, we need to change datums. Pathfinder office will change datums “on the fly.”

2. The Mount Pleasant DRG that you will be using is georeferenced in the UTM coordinate system, 16 North, NAD 1927 (Eastern U.S.), GEOID96 (Conus). Thus, your maps must match the background map.Place this information in Pathfinder office by first clicking “Options” on the main Pathfinder Office Menu and then “Coordinate System.” A “Coordinate System” window appears. Set “Coordinate Units” to “meters” and “Altitude Units” to “Meters.” Set all other appropriate information. It is only after setting the right coordinate system that raster files like DRG’s will properly display.

3. To load a background file, select “File” and then “Background.” A “Load Background Files” window appears. Click the “Add” button. An “Add Background File” window comes to view. Open the Mt. Pleasant DRG from K:/courses/esc334/Francek/mt_pleasant. Click “Open.”

4. A warning window appears stating the importance of setting the datum for this DRG. Click “OK.”

5. A “Load Background Files” window appears with the Mt.Pleasant quad. Highlight the quad name to see that the coordinate system of the background map matches your Pathfinder map coordinate system. Click “OK” and after a progress bar appears, the quad will appear as a background file. Does the DRG accurately portray your position?

E. Plot a Pathfinder Office Map
  1. Select “File” and the “Plot Map” options.
  2. Enter a title for the plot,
  3. Click Preview to see how the map looks before it is actually plotted. Center the map and choose a scale that will show your features in detail yet show significant campus landmarks. Close the preview window.
  4. Click “OK” to plot the map and then, if acceptable, click “Setup” on the “Plot Map” window to print on the Ink Jet Color Printer. Include this plot as part of your exercise.

The following questions will be collected a week from today.

1. What is the horizontal and vertical precision of the southern most spring?

2. Record the UTM coordinates for the northern and southern most spring.

3. For the northern and southern most spring, what is the difference in meters as indicated by the "north" UTM values?

4-6. How close was UTM distance from #3 compared with the distance derived from the measurement tool? Should these values be similar? Why or why not?

7. What is the 2D length of both stream features?

8. What is the altitude in feet of the first and last points in the meandering stream?

9-10. Record the wetland's 2D area in acres, square meters, and hectares. What is the 2D perimeter in feet?

11. Discover and record a definition of PDOP (Position Dilution of Precision).

12-13. What is the difference between accuracy and precision?

14. Print out a plot of mapped area that can be stapled after to the quiz.

*All images courtesy of Trimble Navigation Company, 1999. GeoExplorer 3 System CD, Sunnyvale, CA.

1