GPS and Total Station used together (Land Surveying)

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

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.

--
If A is success in life, then A equals x plus y plus z.
Work is x; y is play; and z is keeping your mouth shut.
Albert Einstein

Craig B. Davenport LS,PLS

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

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.

--
"You don't have to be a good surveyor if you find all the corners."

Kris

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.

--
Ex tenebris ad lucem

LinkedIn profile http://www.linkedin.com/in/scottpartridge

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

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

Some other things to consider:

Are you using a 1", 3", 5" or 10" total station?

I assume you are taking at a minimum Forward, Reverse, Reverse, Direct observations for each traverse point. If you want to tighten up your traverse work, add more sets.

Do you see any abnormally large residuals on adjusted angles in your traverse (assuming you are using least squares)?

Lots of factors to consider here.

I hope this helps.

EDIT You can find some good information here. I am not sure if this is pertinent to your project or not, but some good food for thought anyways.

For the original question: If you have to ask it is apparent you need more experience working under a qualified professional to understand the many procedural and mathmatical relationships in play with an apparent attempt at acheiving high order results. To achieve high order results with consistency, you first have to understand completely the methods, procedures, equipment and mathmatics involved.

Traverse accuracy and precision is the base upon which a surveyor is built. To not understand that is a sure sign the basics have not yet been learned.

After you set your GPS points did you compute a combined scale factor to apply to your total station traverse . In my area of NC in 13,000 feet I would be looking at .06' per 1000' so if I did not apply scale factor I would see around .78' in horiz error in 13000'.
For your elevation error I would set more checks along the route . Trig leveling can be a problem on long traverse loops . You need to keep the traverse legs under 700 feet for elevations to be decent. Your GPS has better elevations over a longer distance than your conventional traverse . Go Back and do static GPS session on the control points . You will have a great elevation check .

Double all angles on your traverse . run all through least squares .

Are you able to RTK you traverse points from the beginning to the mid-point? If your data consistently gets worse as you progress, it's probably a scale factor issue.

Combining EDM traverse data with gps data over a long distance is tricky. I'm assuming you set up you GPS autonomously, calibrated to known control and then took off with you traverse. Set up a new job for EDM work and set the scale factor to one. You may be able to manipulate the data, but if it were me, I'd eat it and run the traverse again.

....sunshots

We scared him away, dang it, now we'll never know how the ending goes...