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Settings GCP's with a total station - Traversing or Stakeout?


(Christian Grüner) #1

Hi,

While not directly related to the Reach units, I often find myself in spots where I need to place GCP’s, but where buildings or foilage covers are 1-2 meters away from the GCP’s, hence blocking out much of the sky.

I can place many of my GCP’s with a Fixed solution from the Reach RS+ unit, and so I have multiple known points of high relative precision (within few milimeters).

The semi-blocked GCP’s I will place using a total station using either stakeout or traversing (closed or fixed).
But what is the most precise method? Traversing seems to offer an more rigid error-correction, while stakeout seems to be faster?
When traversing, I could some sideshots, but would it be more precise to make this corner points instead?

Time is of course always of the essence, but, this is permanent installation (for volumetric measurements), so I’d rather do it the most precise way the first time anyhow.


(Andrew Yushkevich) #3

Hi @wizprod,

Why these GCPs are so important for you? Why can’t you use others?

Do you usually have float on these points?


(Christian Grüner) #4

I need to outline the piles with GCP’s, and as 1 edge/side borders up to trees and another to a metal building, I need the GCP’s in place there.

Yep, float with an RMS of 0.5 -1 meter, and in some cases single.


(Andrew Yushkevich) #5

Quite tricky :slightly_smiling_face:
Have you tried higher Elevation and SNR mask values could help?

Also, can you share raw logs of the test?


(Michael Lambert) #6

You should be able to traverse and shoot in normal topo shots. With a gun it should be as quick as 3 seconds. What system are you using?


(Christian Grüner) #7

I can send you the dataset in a private message, as I can’t disclose the location publicly.
It is the same dataset as in this thread (the rover one, however): GLONASS outtage, GPS fine, what went wrong?


(Christian Grüner) #8

It’s an “older” Pentax r-325ex (5").
Normal topo-shots = 2 known points and then shooting the GCP ?


(Michael Lambert) #9

Traditionally it would be 3 points (occupy/backsite/check), but if you are confident in your points the two will work. Do you plan on creating the points to occupy with your GPS? Or do you have YXZ control already?


(Christian Grüner) #10

Plan on using the RS+ to generate the points. There are a few spots there where I can get a solid solution. Will have to place a few more to get a proper backsight (that is long enough away).
Relative precision is fine, no need for absolute (though there is a commercial NTRIP station 900 meters away, but their fee is out of my reach…)


(Christian Grüner) #11

Have sent you a link for the logs as well as a few other resources.


(Michael Lambert) #12

I know you know what you are doing with the RS+ so considering the gun will be low hundredths you will be fine.


(Christian Grüner) #13

Low hundreds in terms of distance?


(Michael Lambert) #14

In terms of accuracy. I would expect a 5" gun to shoot within 0.05ft or 1-2cm.


(Christian Grüner) #15

that’s is my hope as well. It need to be down in the error-margin for it to be good enough for GCP’s (if I want sub 1% errors in my volume estimations).


(Michael Lambert) #16

That’s pretty tight. Stockpiles, grading, other?


(Christian Grüner) #17

Stockpiles, 3000-8000 m3 per pile. anything above 1-2% error suddenly becomes quite a big volume (in absolute terms at least).


(Michael Lambert) #18

Totally agree, that’s about the size of our average stockpiles. Bigger land development jobs get up around 15,000, but that’s probably only 25% of our work. Right now I work at about 2-3%, but that’s without PPK/RTK on the drone so I hope to improve.


(WSURVEY) #19

I actually prefer sideshots. Reason being, if done properly, it can be more accurate. Situations where the highest level of precision/accuracy is required, like industrial measurement/metrology, almost never have anyone traverse over the point(s) to be measured. You couldn’t achieve the extreme precision/accuracy relying on optical and laser plummets, and box-tapes for height.

Having said that, with your “older” 5" pentax the difference between occupying and sideshots will be not worth worrying about.


(Michael Lambert) #20

@wsurvey, What is your definition of a sideshot? To me this is a 4th gen point. 1st gen is the original benchmark or control point. 2nd gen are all the points you can shoot from that 1st gen point that are level-looped to create the primary control network. 3rd gen are all the secondary control points that most of the layout is done from which in this case would be the GCPs. 4th gen would be the sideshot that is never intended to be part of the network or shot from. These are the least accurate of the network and should never be part of a localization. Everything after the 1st gen point is technically a traverse point.


(WSURVEY) #21

hi chascoadmin,

my definition of a sideshot is a radiation to determine coordinates of a point. a point not ‘occupied’ by the instrument.

in your world that sounds like it’d be a traverse point of 4th gen.