We do this all the time. I “pre-calculate” the locations of monuments we will look for in the field. I use a grid system that starts at 20000/50000. Each of these points has numbers from 1 to 199.
We go out, find a controlling monument we are satisfied with as far as safety and security.
For example purposes, let’s assume we’ve found points 3, 5, 7 and 9 and we’re setting up on 3.
Set up the base over the point and fire up the system. We tell the DC that the base is on 3. When FG2006 asks for the measurement, I select Localize mode (It’s not in my hand so I can remember the exact wording of the screen). Record the shot as 303 (we just add 300 to the point number in the file to segregate it from the “Control Point”.
Then, we fire up the rover. It gets set up on 5, 7 and 9, consecutively. Each time, we take an RTK shot, storing it as 305, 307 and 309, respectively, in this case. Before the shot is completed, we check the box the use the point as a localization point (second box up from the bottom right of the screen). If the shot gets taken and moves to the next screen before I get chance to check the box, I hit cancel, which takes me back to the previous screen with out dumping the data (unless I hit cancel twice).
At this point, the DC want to know what to pair the current shot with as far as the control cords. Enter the number in the box, select the number from the map screen or enter the coordinates in the appropriate boxes.
When you look at the next screen, you’ll have the adjustment points displayed. They should be paired up with the “shot” points in one column and the “control points’ in the other.
Tap “Calc Parameters” to get a look at the LSA residuals for the network. As long as they look fairly intelligent, tap OK and go to the next screen.
Here, you get to look at the scale factor and the rotation from the calculated points to the control points. Unless things look really screwy, tap on “ADJUST Points” in the upper right hand corner of the screen.
You should see the DC go to work moving the lat/lon based shots to your control points.
It does take a bit of getting used to until it becomes second nature. Senor Poitras needs to revamp this portion of the manual and put together another nifty video to cover this a bit better under FG2006. However, he is a busy man! ;^)
The main source of error we find is that we are not on the points which we think we are. This leads to some very interesting scale factors well away from 1.
What I find most interesting when following the old GLO surveyors who carried their bearings forward from early morning sun shots is that the rotations are often just a few seconds. Rather amazing for the the equipment they used and the equipment I get to use today.
I hope this helps you out, Chris.
I’ll be back in the field again tomorrow doing exactly this kind of work. I’ll make sure I take better notice and notes and post again if you need it.
Ian Wilson Land Surveying, Inc.
Temecula CA 92591