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GPS Verticle hit and Miss ???

Posted by Jim on May 10, 2009 at 7:30am
Comment by Jim 1 second ago Delete Comment Verticle, GPS is seems undesirable at times. 1/4" - 2' variables. Not good when your putting in Pavement grades, our control. Any one have insight here. I have had time of hitting right on but the hit and miss has got to go , Right?

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Tags: gps, pavement, vertical
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  • Gary Breisch May 11, 2009 at 8:00pm
    If you take the same care to make sure you localize and then check at least one and better more depending on how often you visit the site, you will get good vertical. If you localize on two different points that are not part of the same control or datum then you may introduce a "tilt" in your GPS model and get what you say you got. As much redundency is needed in your GPS as your other equipment.
  • Gary Breisch May 10, 2009 at 11:51am
    What procedure do you use to setup and localize and check into your local control?
    • Jim > Gary Breisch July 5, 2009 at 10:30pm
      I usually take ahalf dozen shoots on known local control and then solve localazation or Calibrate depending on what software I am using.
    • Jim > Gary Breisch May 10, 2009 at 8:57pm
      I take the .job file and into my TCS2 and go out and shot 6 control points if available and then using TDS ground localization I solve, calibration. Sometime I am right on sometimes I am not.
    • Gary Breisch > Jim May 11, 2009 at 8:33pm
      I only have problems if I am near to solid objects like buildings or large trees. I use my Magellan ProMark3 RTK (PM3RTK with static to set really good control and process it right there at the site with my notebook computer and GNSS program.

      If I have to set points in tough places I set a couple of cotrol with static near those areas and pull out my total station to set them 3d with the same data collector that is built into the GPS (Carlson Fast Survey.

      I tested the GPS and ran both systems for two months to test it and make sure I had the right redundancy check procedures in place before I used the GPS exclusively on my projects. The PM3RTK does not have very powerful radios so I limit the area that I do RTK and use the Static to set control in large areas and move my base over to the various parts of the large area if needed.

      All the work I do myself so I do not have to worry about figuring out mistakes by others and have eliminate communication problems, costs, and time, LOL. Magellan ought to pay me for all the analysis and techniques that I have developed in the practical use of their PM3RTK. I really maximize on my relatively small investment for my first GPS equipment.
  • Montano May 10, 2009 at 11:02am
    Jim, GPS is really not the ideal tool to use when it comes to elevation. The error is to inconsistant. GPS is a great tool when in comes to X, Y measurements but not Z.
    Elevation I measure with either my Autolevel or Total station, Using those two instruments there is no guessing.
    • Jim > Montano July 5, 2009 at 10:34pm
      Ye I guess this is where we are at this time. I am doing a job right now that we used GPS exclusive. It checks in at many different areas a large project that GPS is perfect for wide open space and plenty of work long distances from each other.
    • Jim > Montano May 10, 2009 at 8:56pm
      Refreshing! I use the robotic s6 to check in I also have a geodimeter and a theadolite that I use aswell. I wondering with the new L5 signals and stronger radio will we get better?
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