RTK Control

[coast]

We received a set of railroad plans today to prepare a cost proposal for construction staking.

In reading the control notes on the plans, the PLS stated that he established both the vertical and horizontal control for the project using RTK from one control point.

Is this practicing outside of your area of competence?

[pls7809]

There was a job we were supposed to do, but ended up not (dodged a bullet IMO). The plans showed four control points all within 100 feet of a RR crossing, which was to be turned into a grade separation. The plans showed a bypass track being constructed beginning about 1/2 mile each way from the proposed new grade separation. No control provided except those four points immediately near where the new bridge was to go. Chances are those four points were in danger of being destroyed by the construction. Who plans stuff out like this?

[Brad L]

I was always told to be twice as accurate as the person coming in behind you. So if building railroad tracks do not have strict construction specs, the control would be sufficient and within the required area of competence.

While the control procedure seems loose, it is most likely accurate relative to each other. If when verifying the control and its tolerance are outside the project specs, submit a RFI to the design engineer. If you feel the answer will not satisfy the project requirements, tell the general contractor to issue a change order.

[coast]

This is definitely practicing outside of your area of competence. A competent surveyor would realize that:

First of all, using one control point to establish project control is not a very accurate procedure. Actually you would have no check of your work at all.

Second, using RTK to establish horizontal control for a project is not a very accurate procedure.

Third, using RTK to establish vertical control for a project is totally not a very accurate procedure.

Fourth, each RTK position is totally independent of the next so, again, you would have no check of your work at all.

Fifth, this seems to me a general lack of understanding of how to perform basic control work and a general lack of understanding of GPS accuracies and procedures to establish project control.




Brad: Since each RTK position is totally independent of the next so it is pretty much impossible that "it is most likely accurate relative to each other".

[Tracy Park]

I wouldn't challenge the other surveyor's area of competence without at least giving him a call and talking with him.

[coast]

Call him to discuss what.? His work seems to stand for itself.

[Brad L]

If you already knew your answer, why did you post the questions? Seems very pointless. However, the information you provided from your first post lacks the detail you provided from your second post. Please provide me with some clarification;

-"using one control point to establish project control is not a very accurate procedure" is not a true statement for absolute accuracy. What if they had the base running for hours and re-observed the project control multiple times, could that not be accurate enough for this project? This is a hub network design. Where you precisely and accurately determine the position of a single point, and then process the independent vectors relative only to that single point. {edit}

-Using RTK to establish horizontal control is not "very accurate", so then what are the accuracy requirements for this project? thousandths, hundreths, tenths, feet, tens of feet, ....?

-See above for vertical.

-You know for certain they did not re-observe their control from a single base or perform any type of check? The notes stated after setting the control, they did not set up a total station to verify the angles and distances?

-How did your observations of the control compare to their?

-You haven't talked to the surveyor, but notes fully describe how they established the control.

Coast: I will have to disagree that "it is pretty much impossible that" it is most likely accurate relative to each other, but I do not know the field conditions nor the procedure used by the surveyor to set the control. I personally, would never set construction control using RTK, but do use one control point to establish project control by static observation and it has proved time and again accurate enough for our horizontal requirements (typically vertical too, but I still run levels through it).

Also, it sounds like you need to talk with the other surveyor. If nothing else, to try and obtain the observation files. I still stand by my statements about RFI or a Change Order if the control does not match within the project specifications.

[Proud7191]

Call him to discuss what.? His work seems to stand for itself.

You worry me! Give the guy the benefit of the doubt, talk to him. He probably had no control of what verbiage was placed on the plans. Jp

"As you think, so you become.....Our busy minds are forever jumping to conclusions, manufacturing and interpreting signs that aren't there."


Epictetus

[Jim Frame]

I agree with Brad L: RTK *can* be used to establish accurate H/V control, though it may not be the most efficient way of doing so.