Collecting Data at a Point with the PRO XRS System

If you changed some of the configuration settings to values other than those suggested in Configuring the GPS, some of these steps might come out a little different; just think them through as you go. My assumption is that you will create a new, unique file for each station that you occupy.

1. Collecting carrier-phase data that will be post-processed - this assumes that, in Configuring the GPS - logging options, you set Carrier Mode = ON and Minimum Time = 10 minutes and that you want submeter accuracy for your observation. This is the typical mode for environmental scale gravity observations. My choice of 10 minutes results from a number of experiments in trying to determine the standard deviation of carrier-phase, post-processed points. Treat 10 minutes as a minimum amount of recording and reoccupy known locations (benchmarks) in your survey area to estimate the standard deviation of your observations. Sometimes, depending on how many satellites are visible and what your allowable uncertainty is, you can get by with less time.

From Main Menu, go to:

• Data Collection - hit ENTER
• Highlight Create new File, hit ENTER and the Create new File menu opens up and presents these choices:
  
  • Filename - use the suggested filename and you will always know the day and time of the data. In your field notes, record the name of the file and note where you are and what you are doing. The data recorder provides an opportunity for you to put all such information into the unit. To do so, read the manual's chapter on Data Dictionaries and create and upload a data dictionary suitable for your survey.
  • Data Dictionary - select Generic unless you have created your own (as above).
  • Storage disc = TSC1 means the data will be stored on the data collector
  • Free Space - tells you how much room is left. Remember you can always delete any data that is on the recorder when you check it out and go to the field.
  • Highlight the Filename field and hit ENTER
    • You are now in the Start Feature submenu. Make sure that the receiver (antenna) is where you need it for your observation and then highlight Point Generic and hit ENTER. This is when Trimble starts collecting data!! THIS IS WEIRD until you get used to it because there are some subsequent menus to deal with.
    • The data collector now presents an opportunity for you to enter a comment - do so if you wish to store some information with the data you are collecting. DO NOT HIT ENTER UNTIL YOU ARE FINISHED COLLECTING DATA AT THE POINT OF INTEREST! As soon as you do hit ENTER, the recorder stops collecting data. If you do hit ENTER too early, you'll get a chance to back out of your mistake if you have not collected the minimum number of GPS positions set in your configuration - logging options. If you want to go back to the Main Menu while data are being collected, use the MENU key.
    • HIT ENTER ONLY WHEN YOU ARE DONE COLLECTING DATA AT THE POINT and you should be returned to the start feature menu. The longer you collect data the better your average position will be and the better you will sample the standard deviation of the positions. My experience and experiments indicate that the standard deviation, with PDOP < 8.0 and usually <6.0, is on the order of two meters or so but it can be twice that before post-processing which generally yields submeter results! Do your own tests, and keep track, if the results/values are critical.
  • Hit ESC to return to the Data Collection Menu and you are ready to start another file at another survey point.

2. Collecting carrier-phase data that will not be post-processed - this assumes that, in Configuring the GPS - logging options, you set Carrier Mode = OFF and that the nominal standard deviation of > 2.0 meters will be adequate for your purposes. I have seen the non-differentially corrected standard deviation as large as ~ 5 meters so beware. Everything goes just like the above except for the setting of Carrier Mode = OFF.