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Orientate instrument using two unknown but accessible traverse points.  

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OK , this thing is called free station . 

It gives you the freedom to put the instrument wherever, calling the standing point 100,100,100 or 10 and orientate your instrument to one Control Point of the traverse , and foresight the next one.

This is how I understand it. But you actually are doing a resection. I just don't get what kind of transformation is involved between my arbitrary point or points in case I do this for a long - big project , and the lets say OSGB36 . 🙁 

Gosh I hope I have got it right so far. Please let me know what do you think 

No you haven't... 

What don;t you understand from all the advice that has been given?

Freestation is the same as resection and is used once you know the coordinates of the points.

If you don't have any coordinates when you are in the field then you  just measure the station points using an invented local coordinate system. The adjustment can then be done later.

I described before how to set up on a invented local system.

Presumably this job should have been done by now? You might want to involve someone more experienced to show you the ropes.

Why have you not been given coordinates to work from? It seems like your skill level is not up to starting a survey and tying into the previous work. You might be better off demanding station coordinates before you go any further. If they are OSGB36 then Access will use the correct scale factor once you choose OSGB36 as the coordinate system. They need to be proper OSGB36 though, generally I find that scale factor 1.0 has been used even if the coordinates appear to be OSGB36.


Here's how I'd do it.

Set up inst. on arbitrary 50k/50k and set a nail there. Then, using a magnetic compass, observe the direction to one of the control stations, with a distance, reduced to horizontal. 

Then, using that ctrl point as a backsite, I'd zero the inst on it. Then, turn angle to the other ctrl station, and measure the (reduced to horizontal) distance.

We can call the inst point A, the backsite B, and the fireside C.

Now, we have a triangle. With a bit of trig, we can compute line B-C. Let's say we find it to be N12ø13'14" E 822.56'.

Now, we go find the prev coord for these ctrl pnts. And, that the brg is N13ø15'20" E 822.60'.

We now rotate pnts A B and C so that line B-C matches the prev brg. 

We now can make a mid point between B and C.

We also make a mid pnt between the original ctrl pnts.

We now translate points A B and C, and the mid point, so that the mid points of our control match the mid point of the control stations. 

Now, my point is this. All the above is very normal for any surveyor. A standard exercise. Are you an engineer? Or, a student, or what?

Why do you come ask to borrow our every day tools, that we make a living with? Not that we are bothered by sharing, but if we have to spell this out for you, you just might be in water too deep for yourself.... 

Take care,



Surveying is more than a Job----it is a passion to provide a foundation for future generation, that is beyond reproach.


wow that's complicated!

but he doesn't have the co-ords for the points or even a bearing between them so no rotating or anything else till he gets them.

i think he's an engineer starting out. had some teaching at uni but not really got a feel for it yet. needs some help from someone on the ground.






Javad GNSS


He has the TOPO in CAD!

my way would be to open the cad file, have a look at both control points, make sure there is a simple 3D-point on each one, a line between both would be fine but not really necessary. Make sure the point name is as text readable and save as dxf to use it as map in Trimble Access on the tsc3.

on site use the resection station set-up, give your station the desired name (no assumed E,N,El), tape you HI., go to map view, select your first control point, switch to resection, in the name field for pointclouds shoot select the option ‘Select from Map’

since you already selected that one point it will be added for you’

repeat for second point

select calculate and you’ll be presented with the error values of your resectionand if ok with the E,N,El and your Azimuth, and you can start shooting other pointsin the same reference frame of your control points.

if you have all data digitally available use it digital and keep away from keying in manually! Humans make to many misstakes, computers don’t.



A part of my answer is wrong. You will need to use 3d for it all, and keep track of elevations. It's just getting deeper. Not hard, but I honestly suggest you get a bit of help... In person.

Surveying is more than a Job----it is a passion to provide a foundation for future generation, that is beyond reproach.


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