Title: Converting GPS Rover Files into ArcView Shapefiles and Adding Them to Your GIS Project

Date: April 23^rd, 2001

Purpose: The purpose of converting the Trimble Geoexplorer 3 Rover files into ArcView shapefiles is that it allows for field data collected using the GPS unit to be properly displayed in ArcView. When converted into shapefiles, the data dictionary created for the fieldwork will be maintained and be displayed as the database file (theme table for the appropriate theme) in ArcView. The steps outlined below discuss how to transfer GPS data to your P.C., the process to perform differential correction on your data, and the procedure for converting and displaying GPS rover files in ArcView as shapefiles.

Software requirements: Pathfinder Office, GPS Receiver, GPS Support Unit, and access to an Internet Browser (Netscape of explorer)

Procedure:

v Transferring Data to the PC

· Place the GPS Receiver in the Support Unit

· Open Pathfinder Office and select Utilities/Data Transfer

· The file(s) generated from your fieldwork will display in the Files Collected window

· Highlight the files you want to transfer and click the Add button

· Make sure you have specified the correct destination directory prior to transferring the files from the GPS unit to the PC

· Click the Transfer button, and click on Close when the transferring process is complete

v Deleting Rover Files

· It is a good practice to delete files in the GPS Unit after they have been transferred into Pathfinder Office

· Press the Data button see Data files

· Press the Option Button, select the Delete Files option, and press the Enter button

· Select the files to delete and press the Enter button, once to delete, and a second time to confirm deleting the file.

v Setting the Coordinate System of the Display

· The coordinate system of the display can be changes by selecting Options/Coordinate System form the toolbar menu in Pathfinder Office.

v Differential Correction

• Click on File/Open to open the Rover file in the map window
• Select Utilities/Differential Correction to obtain dialog

• Select from Local Search if base station data is stored locally (if you have GPS base station)
• OR; Click on Internet Search if base stations are at a public website. The dialog will list available sites:

• For Bellingham, WA, closest sites are CORS Whidbey or SEDR – Sedro Wooly
• The program will select the files that match the data and time of your files collected in the field. Click on OK to download base files. Click OK when confirming each step.

• Then click on Search to find the base files that match the time of your rover files
• If a match is found, a Confirm Selected Base Files dialog appears
• Click OK to confirm, then the dialog returns to the Differential Correction Dialog
• Click OK to perform the correction
• Click on Close when the correction is complete: The new files will have a .cor file extension and will show in the map view

• If the download is not successful, make note of the file names (e.g. whd11040.00s) an then use FTP to transfer

• FTP transfer can be done from ftp.ngs.noaa.gov as Anonymous
• Once in the FTP site, navigate through cors\rinex\ (date and name of file) \whd1 or \sedr

• [pick the data – 1000209 is Feb 9, and check the time of posting – in Bellingham we are 8 hours later the GMT. The name of the file is the day of the year; e.g. 0055 is Feb 24^th.]
• \whd1 [for Whidbey site. At this point scroll down to the files you noted above.]
• \sedr [for Forest Service Sedro Wooley Site]

· Save information to the Base folder of your project. Then you can browse in Local Search. If searching for the previous day, the files you need are the top three – e.g. whd11140.00n (letter for the hour is replaced by a 0 for the whole day), whd11140.00s, whd11140.00o – or they may be the only three, if more than a day or two old.

v Adding Corrected Data to Your GIS Project

• Use Utilities/Export to get a dialog that shows file names of those shown on the map, and the directory

· Select Sample ArcView Shapefiles Setup in the Choose an Export Setup box.

· Check that the coordinate system listed in the window matches that of the map to which you want to add your data. If necessary, change the coordinate system:

· Click on Change Setup Options button to get the Export Systems tab;

· Click on Coordinate System tab;

· Select Export Coordinate Systems radio button, then Change box;

· Select the coordinates system desired (e.g. UTM, Zone 10N, NAD27)

· Click on OK through the dialogs and shapefiles are created for each feature. You may have to change the folder if you see a warning that files could be overwritten.

· Note: If you export uncorrected data you must change the Position Filter in the Setup Conditions to include Uncorrected Positions.

· The file can then be added to your ArcView project using the Add Theme icon, or by choosing View/Add Theme.

· Note: The file will be added to your project as a shapefile, but it is recommended that you convert the imported file into a shapefile to ensure that all your data is contained within each of the newly imported files. Once the files have been converted, you can move to another machine and display the shapefile themes in ArcView.

Conclusions: The methods described above for transferring your GPS data to your P.C. unit and then converting the GPS files to ArcView shapefiles greatly enhances the accuracy of data, but it primarily enables you to use field data in ArcView. This process, as described in the purpose, helps to begin database development for features collected while in the field. This process reduces time and frustration of finding and properly converting files into formats recognized by ArcView.

Note: While Pathfinder Office is still open after converting Rover files to Shapefiles, it is recommended that you open a view in ArcView, display your newly created shapefiles, and then convert them to shapefiles in ArcView. This will ensure that no data is lost and minimize the need to re-convert the original rover files into Shapefiles a couple of days later, or when moving to a different computer.

Created by Chris Connell and Andy Freed, Geography 452: Advanced GIS Class.

Adapted form Jim Talbot’s procedural outline titled “GPS Mapping With The Trimble GeoExplorer 3”, provided by Gene Hoerauf.