Hello,
RTK GPS Job, construction of 3 kilometers of gravel road. I have a control file with points that have:
-Horizontal component: UTM grid
-Vertical component: Orthometric elevations
Slope of geoid is 8 cm/km along +/- the direction of the road. Control points are 300m apart. Control points are a combination of 1 geodetic monument and newly (2 year old) established re-bars. The ground is known to move in that region.
How would you go about setting up the coordinate system?
1. One-step transformation with a few of these points control points (treat it as a local site), no geoid model applied. Let the program do a best fitting tilted plane.
2. One-point one-step transformation (with geoid model applied) using the published value of the solid, deep in the ground governmental geodetic monument.
3. Treat as a grid job (just set up base and treat ellipsoidal heights as elevations) and include the geoid model in the rover to control the vertical component.
Just looking for a few comments from GPS experts, there are many on this board.
Thank you,
Georges
No. 2
Is you project "staying on the road"? If you have side streets that will be part of this project and all of your control is on the road you will need to watch your vertical. When I have long straight lines of control I only hold one vertical control point and check into the rest. If you use them all it will screw with your vertical plane.
If your project control is already in UTM grid, I would go with number 3 as long as the control points checked well between each other.
I agree with Dave...Option #2
I will however get my 2 bits in about VERIFING the existing “control.”
Start by setting up on the “Geodetic Station” and entering the UTM coordinates and Orthometric Elevation into the Base Station. Be sure that you are collecting static observations at the Base and using the "right" geoid model.
Start at one end of the project, and do [say] 5 minute RTK observations on each “Rebar” (with a bipod) from one end of the project to the other (this will take 1-2 hours depending on various factors).
Go back to the first Rebar (now an hour or two later), and repeat.
Take this data, and compare these N/E/O results with the “Control File.” If everything looks GOOD [enough], then you are ready to rock-n-roll. If NOT, then THIS is the time to figure out what is wrong!
Obviously if the project has been designed based on CRAPPY “Control data,” then you are going to have to figure out some form of “best fit” scenario, and work from there.
Loyal
project is staying on the road
thanks folks for the replies,
:beer: