Dear Paul and others,

Offcourse all GPS will give only Position accuracy only, My Question is Just after establishing the 3 points by Promark3,the included angle of this 3 points should match with Total Station.

But there is some 3 to 5 second deifference,if the difference is like this in all loops/Angles how the traverse will close for the route of Closed one.

Can you give some idea.


Thanks


PKS

First a couple of things are you serious about the 3-5 sec difference in angle between GPS and Total Station?

I am not being funny but what observations did you perform. The following has to be answered:
1) Are the observing stations fixed monuments pedestals.
2) if the anwer to this question is no then there is no need to ask the other questions. because the setup errors have not been eliminated.

Assuming your triangles have 200m legs, 5" difference is 0.005m positional difference. We live with that every day.

Least squares is a necessary tool.

At some point a large project will require a COGO program that can deal in geodetic coordinates.

Please forward some more project information?

Paul in PA

Here is something a father shared with his ambitious young surveyor son. I wrote it in my little book with other sayings from the Wise Old Indian.

***
It is the mark of an instructed mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness when only an approximation of the truth is possible.
Aristotle
***

I can remember a geodetic surveyor who took a geodetic data processor lady to the field for some GPS work. She set up a fixed height tripod for the first time and asked him to check it. She missed the dent in the brass cap by about 0.010 meters. He told her she was off. She thought it was close enough. His response was that she was the one who bragged about 0.020 meter accuracy but she just gave away half the farm.

Can you set up the total station again and set new targets on those points and measure the same angle within 5 seconds? If you can, be sure to avoid using GPS for anything but longer lines or places where you cannot repeat angle and distance measurements closer than 0.020 meters.

Mr Phil,

Actualy Nowadays we are doing all Road Projects here.
My Nature of Job is to provide the control points to the Contractor for their construction activity.(Particluarly X,Y)

So i need to fix TWO intervisible Monuments at starting point of project(Say 200m-300m)and after every 5Km we have to fix another 2 intervisible points.

The Total station Surveyor should run the traverse from the first 2 points and they have to close their traverse(By Establising No of Control points) at next 5th Km Survey(GPS)Monuments.The accuracy of the traverse should be 1:20000 as per scope.Till last year we used SR-530 lieca.Now we are using P3.
Now my Problem is Distance is matching with Total station distance from first monuments to second one.But there is some angle deviation that lead to give the error less than 1:5000 Accuracy.

Even we are observing (Static)40min all the GPS monuments.There is any solution or change of operation style or processing method for the above mentioned problem
Modified By P K Samy on 2/28/2007 at 12:47 AM

PK, I am going to remove my tech support weenie shoes for just a little bit and replace them with my professional surveyor boots.

A 300 meter backsight projected to 5000 meters may not yield the results you desire. But I would stack the accuracy of the ProMark3 positions you can compute over any other tool measuring pairs of points at a 5000 meter spacing. This is not about single frequency v. dual frequency accuracy. I can prove that in the dirt. What I am trying to say is that I trust the ProMark3 measurements more than the total station measurements at the end of a 5 kilometer traverse.

But I am making some assumptions about your work.

A corridor measurement should include measurements of both the short and the long lines. The vectors that connect the individual pairs of points with each other and with the next pair of points down the line are essential to the project.

I can imagine a corridor survey project that looks much like the diagram on page 34 of the ProMark3 reference manual. This is the kind of corridor survey project that Sharon and I did many times. On our projects we measured each of the vectors that are illustrated in that diagram and we measured the short vectors between the pairs. Our projects looked much like a ladder. Each rung of the ladder was the vector between the pairs. The vertical supports were the vectors connecting one pair with the next.

Some talented professionals will tell you that it is a mistake to measure the short lines. It makes a mess of the accuracy ratio. They are as entitled to be as wrong about that as they want to be. I care little about accuracy ratios and a lot about the positional accuracy of the points.

A corridor survey is almost always about the need for control points that will be used to survey features. It seems that accuracy of position is what it is all about.

The method I suggest yields reliable results that I bet Sharon's house on more than once.

Now that my professional surveyor boots are removed and my tech support weenie shoes are back on I will suggest a visit to the ftp server at

ftp://ftp.magellangps.com

to get the file named Practical GPS Surveying from the General Info folder.

"They are as entitled to be as wrong about that as they want to be."

Hey, is that kind of like saying: "Thats just my opinion, yours could be wrong!" ?

I second the suggestion to download, print and read the "Practical GPS Surveying" document as mentioned. Well worth the time.

However, with regard to the problem at hand with the total station traverse, I'd eliminate all systematic errors I could from the git-go and that would include checking the instrument adjustments as well as the prism poles/tribrachs and if you aren't using a 20# all wood none of this hi-tech man made garbage tripods that is so tight that the legs "creak" when you open 'em then there's your problem.

Surveyor boots off now.

Dangerous Dave
Modified By Dave Huff on 2/28/2007 at 11:20 PM

Dave,

Yep, you got it accurate.

Opinions are a lot like noses.

Everybody I know has one.

I don't spell "nose" the same way you do, Phil...my dictionary has it with more letters, beginning with the first letter of the alphabet......

Cabin fever here, alright...
Modified By Robert Bills on 3/1/2007 at 6:33 PM

Getting back to the post, what geodetic system are you using? A projection? A plane system with local coordinates? Is it possible you are seeing geodetic inverses along the curve of the earth, not plane coordinate inverses?

Backwards and forwards azimuths are a joy to work with....

Bob, I was just trying to keep it all family friendly while at the same time trying to say that experience doing traverse work as a Southeast Asia War Games Participant tells me that a five kilometer traverse down a road is more likely to contain error than a 5 kilometer GPS vector.

I was not with PK on the day they did the traverse but I have worked in climates that included some high humidity. Maybe PK was high and dry and angles repeatable at 5" are likely. I cannot say that I could repeat angles at 5" doing survey work in Quang Tri Province. But there were several issues we had to deal with. I am only guessing that PK is working in a hot and humid location based on my simple minded perception of his geography.

I also claim some experience working on a corridor GPS project that ran from Alexandria, Louisiana to Nederland, Texas. That is another place where the air is nearly as thick as the moss in the tree branches.

Over a traverse length of 5 klicks it seems unlikely that there would be many problems related to geodetic v. grid but that may also depend on where they are working on the grid and at what elevation.

I am also thinking about the three words that guarantee accuracy with any measurement.

"I am also thinking about the three words that guarantee accuracy with any measurement."

???

Ok! What?

Jules, you made my day!

The three words that guarantee accuracy with any measurement are:

Redundancy. Redundancy. Redundancy.

Those words were shared with me by a hard headed survey chief in 1971. I called him Indian Territory because he would say, "Saddle up, boys, we're goin' to Indian Territory!"

He is the fat bald guy with the big grin in the photo on the web page at

http://www.8th-4th-arty.com/images/p-74.jpg

Some time today I am going to start a brand new job file and make some redundant measurements to fire hydrants using my MobileMapper CE with Carlson Software GIS-CE.