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GPS and Total Station used together

Discussion in 'General Land Surveying' started by yyamahayzf, Mar 25, 2011.

  1. yyamahayzf

    yyamahayzf 4-Year Member

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    I am using a Trimble R6 using TDS Pro to set control points at the beginning, middle and the end of a job. The total distance of the job is 5 miles. After setting these 6 control points with GPS I am currently running a traverse between them. I am half way through the traverse and when i came up to the middle set and missed the points by .45 on the northing, .25 on the easting and .44 on the vertical. Is using the GPS in conjunction with the total station the right procedure when known points aren't available?

    Thanks everyone in advance for your help :-)
     
  2. Randy Hambright

    Randy Hambright 5-Year Member

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    No matter the brand of GPS or Total Station, I highly suspect you have some bad GPS data.

    That being said, I hope you have checked your total station and GPS against some proven baseline before this job was started.

    A simple check will head off a complicated problem.

    Randy
     
  3. yyamahayzf

    yyamahayzf 4-Year Member

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    At the end of the job, we had previously did some GPS work and before setting the points with GPS and we hit the points and the bench for hundredths. When setting these control points with GPS i shoot the points 3 times and take an average over a period of time.
     
  4. Just Mapit

    Just Mapit 4-Year Member

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    Using GPS in conjunction with any survey you have to do some checks. Was there mission planning? Are you using RTK? (it sounds like your are)....trust your total station info more but only after the Q/A is done. RTK (if that is what you are using) can be skewed if the proper mission planning and attention to the info being produced is not given.

    GPS can be a good check to traditional methods...and vice versa. You found something...that's good....it means you checked it to another method.
     
  5. Brooks Cooper

    Brooks Cooper 4-Year Member

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    If your measurement issues involve local multipath then you will receive those errors no matter how many times you repeat the measurement.
     
  6. Dave Ingram

    Dave Ingram 5-Year Member

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    Do it all the time. Works great.

    Here's an article describing how I do it:

    http://www.amerisurv.com/PDF/TheAmericanSurveyor_Ingram-TheTotalizer_November2007.pdf

    The tOTALIZER
     
  7. Plumb Bill

    Plumb Bill 5-Year Member

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    Scale factor?
     
  8. Just Mapit

    Just Mapit 4-Year Member

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    Agreed...hence mission planing.
     
  9. Kris Morgan

    Kris Morgan 5-Year Member

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    One word for what you're doing "static"

    First, assuming you're in the middle of the project, are on the grid (scale factor)
    Did you make a sun shot after the first mile (two miles is a long way turning 180's)
    Were the control ponts static or rtk?

    What you're proposing is done all the time. Rtk wont cut it though. Checks need to be closer. However, sounds like it closed for a pipline. Adjust and go on.
     
  10. Andy J

    Andy J 5-Year Member

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    are you creating a calibration or localization? If so, they are notoriously weak in a corridor type roadway project. Could you give us a bit more info? are these 6 control points part of a static network? did you send files to OPUS? Those errors are really unacceptable, so there has to be something wrong, don't ignore it.
     
  11. Joe M

    Joe M 4-Year Member

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    You are doing RTK or static GPS? How long are your occupations?
     
  12. itsmagic

    itsmagic 4-Year Member

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    Calgary AB Can
    I've used RTK GPS and total stations on the same project many times using a user defined localization (or calibration as Trimble calls it).

    It works great.

    It is important to perform the localization correctly so the coordinate transformations between the GPS observations and the total station measurements are seamless and transparent. If It is done right you should be able to swap between using the GPS or total station equipment without effort.

    Without more information I'd guess the problem is in how the localization was done at the project outset. Problems with the quality of the GPS positions would be another guess or perhaps incorrect or mismatched prism constants.

    The TDS reference manual provides more detail about the localization process than can be readily expressed here in a few lines.
     
  13. Troy Cobb

    Troy Cobb 4-Year Member

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    My money is on Adam.
     
  14. yyamahayzf

    yyamahayzf 4-Year Member

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    > are you creating a calibration or localization? If so, they are notoriously weak in a corridor type roadway project. Could you give us a bit more info? are these 6 control points part of a static network? did you send files to OPUS? Those errors are really unacceptable, so there has to be something wrong, don't ignore it.

    I am just starting the GPS up in NAD88/83, and i am shooting the control points with RTK, and no i am not send these points to OPUS
     
  15. yyamahayzf

    yyamahayzf 4-Year Member

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    > One word for what you're doing "static"
    >
    > First, assuming you're in the middle of the project, are on the grid (scale factor)
    > Did you make a sun shot after the first mile (two miles is a long way turning 180's)
    > Were the control ponts static or rtk?
    >
    > What you're proposing is done all the time. Rtk wont cut it though. Checks need to be closer. However, sounds like it closed for a pipline. Adjust and go on.

    What do you mean by sun shot?!? The control points were RTK.
     
  16. yyamahayzf

    yyamahayzf 4-Year Member

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    > You are doing RTK or static GPS? How long are your occupations?

    I am doing RTK, my occupations are 3 minutes long with .05 horizontal, .05 vertical and 2 pdop percision. I shoot all six points and go back and shoot all six again 3X. They hold within themselves with the total station, but not when traversing down from one set to another. The average distance between traverse points are about 700 feet with 5 sec of the horizontal and 15 sec on the zenith set for the traverse.
     
  17. Joe M

    Joe M 4-Year Member

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    Do you know the difference between ground distance and grid distance?
     
  18. Guest

    Guest Guest

    Dude!

    You got some scale factor issues is all!

    Gps 1.0

    > Agreed...hence mission planing.
     
  19. Bruce Small

    Bruce Small 4-Year Member

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    I switch between GPS and a total station all the time and I've never seen anything like that kind of discrepancy. My guess would be scale factor, or something similar.

    Except, once, I had a Phoenix file in the flash card and the total station persisted in trying to warp the Tucson data to Phoenix. The errors were obvious, but tracking them down to the stupid file took forever. It wouldn't have happened but Leica sometimes reaches across files to find data it thinks you want. The moral of the story is one file in the card at any time.
     
  20. Loyal

    Loyal 5-Year Member

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    Evanston, Wyoming
    That's an easy one...

    You are:

    1. Using your GPS incorrectly!

    or

    2. Using your Total Station incorrectly!

    or

    3. using your PC incorrectly

    OR (most likely)

    Some combination of the above.

    Tell us MORE about where you are, what you are actually doing, canopy cover, elevations, coordinate system/projection, proceedures, software etc.

    Don't feel bad....You are NOT alone!

    Loyal
     

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