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Dual GPS at Work

Dual GPS at Work
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  • As a young man I lived a life of great adventure.  I am certain that the older I get the better I was.  Now that I am 19 years past the expiration date given to me by the army doctors I count each breath a blessing.  I will give the glory to God and to the young people who will fund my social security checks.


    It is easier for me to control the content of my science projects on my own ftp site.  Access with a web browser is possible using


    ftp://Seeker:[email protected]/disk1


    Alternatively, use a ftp client.   Host:  UserID:  Seeker   Password:  Resources


    Find the project, warts and all, and even more photos that go with it in the folder at




    If you are more interested in the ProMark200 portion of the project it is in the folder at




    I have a lot more analysis left to do on the ProMark200 portion of the project.  My focus has been on the ProMark500 since we got home that evening.  But you are welcome to look at anything on my projects ftp site.


    I should mention that one of the warts is that I did not install a geoid model file that covered the geographic area of the project.  Some of the elevations recorded in the project are actually ellipsoid heights because we passed the edge of my geoid model.  For the purpose of this particular phase of the project that is not really a problem.  I never tried to do an RTK project that started close to home and ended the day so far from home.  So I am also learning things about better planning for a project like this one.  I have a new gsf ready to go and will put it on the data collectors before we make the next trip south.


    One of the nice features in FAST Survey is that I can load a new geoid model and process the raw data file to obtain the correct elevations.  But I am not terribly worried about that for this project.  I will probably do that for the ProMark200 file since I have not yet loaded that project into Carlson Survey.


    If you want some clues about how I measure accuracy take a look at some of my other projects.  There is one in particular that may be interesting to you.  It is in the folder at




    There is another interesting accuracy test in the folder at




    I make lots of mistakes because my mind is getting old and forgetful.  An illness in 2007 left holes in my memory.  Sometimes patience is required just to put up with me.  Every day begins with a morning prayer that includes the following:  Father God, thank you for this day and for one more chance to get it right.  Thank you for my Jeannine who loves me anyway.  Every day I ponder my ability to help surveyors and map makers use the tools effectively.  So far I am sold on the idea that I can do it.  When I can't do that any more my garden may look a lot better than it does now.


  • Land Surveyor

    Phil, I would love to follow you on your journey.  Do you have a place for people to go to follow the progress?  Great photo, but to use the photo as a forum, your journey will be ill-preserved in the annals of the history of land surveying.  If you have a special page for the journey, that's great.  If not, lets get one set up on LSU.  "The adventures of Phil Stevenson, Land Surveyor"  or something like that.  What's your opinion? 

  • The desire for accuracy is one of the reasons why my base station is tied to the National Spatial Reference System and why my RTK measurements get tested against OPUS positions, static survey observations, and geodetic control monuments that are part of the passive control network. Accuracy is about our ability to follow footsteps. I use the term accuracy by intention. How accurate was it? Right now I do not have enough information to make a solid decision about that. I will gladly share the data with anyone who wants to follow my progress. On our trip south from Shawnee my first objective was to test the repeatability over a short occupation time and to see whether I could get a fixed RTK solution. I set the data collector to accept both float and fixed solutions on the first trip. My plan for the next run will be to accept fixed solutions only. I will have a better evaluation of the precision on that trip. There is more to come on what seems like an interesting journey.

    ftp://Seeker:[email protected]/disk1
  • Land Surveyor

    Ahhh, an instrument does not have accuracy at all, only precision. A precise measurement in the wrong location would be precisely inaccurate :)  

  • what is the accuracy of tha instrument?

  • This was our first stop on the trip south from Shawnee, Oklahoma.  This pair of MAG nails is only about ten miles south of the ProFlex500 RTK base station in Shawnee, Oklahoma.  This was a fairly easy leap for the ProMark500 on the left and the ProMark200 on the right.

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Ok. Don't bother me again, for this session.