Is it a good practice to adjust the placement (they are not been destroyed) of the Ground Control Points??

Hi Guys,

I just want to share some concerns with you, about practices on the field.

In the site where I am currently working the Ground Control points were "ADJUSTED" (MOVED is the right word), according with the explanation of the person in charge of the surveying crew. In my opinion and based in my experience, this is not a good practice, instead of, PLACING NEW ONES close to the points that you find are moved can be a better alternative.

Another possible question is: Why do you adjust a Ground Control Point?. Because it is off 5mm.. or 8mm....or more than 15mm...

I do my work using a Sokkia Robotic. The bigger distance is not more than 120 mts.

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I personally would say NO WAY unless you are just starting and nothing has been done based on the position of the points if it has then this could be a nightmare..,

So far, I go along with Jim on this one.  Never remove or disturb an existing survey monument. 

I don't know what the laws say about this within Ivan's jurisdiction, but removing or disturbing an existing survey monument has been taboo since ancient Egypt. 

Along with Jim, it seems, I am of the opinion that if perhaps, during the course of a survey, and before finishing said survey or producing a map of said survey, the surveyor finds himself in error, he should be obligated to remove and restore said monuments to their correct positions.

If an error was made during the course of a survey, and its discovery were to be years later, the legal recourse should be different, depending on local regulations.

So far as I can see, within the original context of this argument, there are no ethical boundaries to discuss. 

Ivan,  would you like to share more about the particular example?  Perhaps we should be discussing this in more detail.


Adjustment by disturbance? It is absolutely a NO WAY scenario.

Adjustment the control points on a closed traverse is common. Never ever move a control point on the ground... ever..Disturbed monuments become reference points, only after you have proved that the monument in question is truly disturbed.

Hi guys,


Thanks for your replies in this topic. As Scott said, I’ll try to be clearer.


I started the layout of this project by adding the Ground Control Points given to us by the surveyors, to my coordinate system. After setting my gun on the best GCP I chose (enough room for the instrument, good view of the job site…. etc.), I started doing BS to all GCP to finally choose the best one (Angle delta less than 3’’, Distance delta less than 5mm). I had performed my work in this way during 4 MONTHS, (foundation, P5, P4, P2, P1). At this time the Surveying crew come to the job site in order to CHECK the work.  The points I was using had not been disturbed, at least apparently, maybe any logic settlement because they are placed close to the cliff. Anyway to be short, after the GCP were “ADJUSTED” by the Surveying crew and my work checked, they found small differences (not more than 10 mm) between my construction lines and the new ones.


As you can see it was not a big deal (lucky man), however, I feel that things were not done in the right way.  The work has to be CHECKED using the GCP I had used, and then ADJUSTED if proved they were out of placement. The Surveying crew “ADJUSTED” the GCP then CHECKED the work.

 Bad practice in my opinion, because a GCP is sacred.


Finally, another concern comes up about the accuracy of a BS taken between 2 randomly chosen GCP’s, I think an Angle delta less than 3”, Distance delta less than 5 mm is good enough. More than those is signal of negligent, Especially if we taking into account this is a “small job” because the biggest distance to measure is not more than 150 m. and on top of this we are using extremely accurate Electronic Distance Measurement devices.


Thanks again for your feedback.




GPC's are to be held true throughout the duration of a construction project.  Construction lines derived from a certain set of control also become sacred.

Adjustment of control in the middle of a project typically constitutes poor judgement. Unless your construction lines were also adjusted, there are now two different reference systems in play; one for construction, and one for some other reason that is not apparent to me.

Did any construction take place before the adjustment of the GCP's?



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