Mock Post
Thanks, I have found a few articles online and I am in the process of trying to figure it out. I WILL figure this out! 😀
Thanks, I will do that. Yes, I learned all I know from OJT and worked at my last job for 12 years, going from file clerk to drafting county road improvement jobs usin Autocad and Eaglepoint. My last boss gave me a computer and a manual and said figure it out, lol. I am sure i will figure this out. 😉
I'd really like to help you, Newt. Trouble is that helping you means doing your bosses work. I don't want to do that for some reason.
Also, giving you generalized advice without knowing more about a) the equipment you are using and the procedure you followed and b) the software you have at your disposal we might just be making things worse for you.
Furthermore, its pretty common to deliver stuff in State Plane Grid. The other surveyor ought to know how to deal with this. So what we have here is not just 1, but 2 idiots racing each other to the bottom.
I understand and thanks for your honesty. 😉
Mock Post
Mockingly: "Mock Post"
Sorry had to do that. 🙂
Mock Post
😛
The very simple solution for this is to place on the plat: Bearings and distances are based on the Colorado Coordinate System, NAD 1983, XXX Zone. 😉
Then you are done, nothing changes. No doubt there is an actual state statute that defines the verbiage for this.
If the other surveyor can't deal with it, he shouldn't be surveying.
This assumes it really is that system.
And unless you are giving out coordinates don't get caught up with epochs, just use the state statute
Of course, if record deed distances (ground) were calculated and held on a grid survey without the appropriate scale factors being applied the survey could require much more than an SPC note.
The PLS needs to be responsible and give this employee the direction they need to complete the task correctly.
what data collector are you using?
You said you found the data in the data collector. Are you going to output the data with ground coordinates from the data collector or downloading and using some desktop software and scale and output the coordinates. There are lots of issues that your boss is responsible for. You could find the scale factor in the data collector, but then where do you apply it from? I would suggest you really study up on GPS surveying So you can be a better drafter. As someone stated you could do this in the CAD software but again the responsibility and issues. Good luck.
There is a lot of good information posted above. The NGS website has a lot of good reading.
First, determine what is supposed to be on the ground: grid distances and bearings or ground distances and true bearings or geodetic bearings.
Then figure out what the other surveyor is using. If the bearings are nearly the same, but the distances are different, then there is a ground distance versus grid distance difference. A combined scale factor could then be used.
If the distances match reasonably close and the bearings are different, then the difference will be grid azimuth versus true azimuth or geodetic azimuth.
GPS will give you grid azimuth and geodetic azimuth. Usually, the difference between geodetic and true will be the LaPlace correction factor. Where I live, it is nearly negligible - around 6 seconds or so. The difference between grid azimuth and geodetic azimuth will be the divergence angle. The value of this angle will increase the further you get from the central meridian.
Also, note that grid north on the East side of the survey will always be parallel to grid north on the West side of the survey. Yet, those same two lines will have a little bit of difference in the geodetic bearings. This will be more noticeable the further apart east-west they are. Think of longitude lines - they are not parallel.
I jumped into this almost three years ago. "Sink or swim." I am still learning! Hope this helps a little. Good luck! B-)
Grid vs. Ground in RTK data collector?
> Hi, my boss went out and did a survey, plotted it and sent it out. Now, another surveyor has come to him telling him that it looks like he surveyed the property in Grid instead of Ground.
Was this an RTK survey, by any chance?
Mock Post
Maybe you misunderstood me. You can probably figure out how to convert the data. Maybe it will then agree better with someone else's. But that could be further from the truth than what you already have. It's an exercise in futility without knowing a lot more facts. Maybe physical markers have been moved or disturbed. Maybe one or both surveys have no redundant measurements and no checks; gross error or mistakes? Has anyone mentioned a closure or positional accuracy or anything like that? I don't think it's possible to really figure it out without help from the boss, not because you're new at this or dumb but because you can't have all the facts.
>
> GPS will give you grid azimuth and geodetic azimuth. Usually, the difference between geodetic and true will be the LaPlace correction factor. Where I live, it is nearly negligible - around 6 seconds or so. The difference between grid azimuth and geodetic azimuth will be the divergence angle. The value of this angle will increase the further you get from the central meridian.
>
> Also, note that grid north on the East side of the survey will always be parallel to grid north on the West side of the survey. Yet, those same two lines will have a little bit of difference in the geodetic bearings. This will be more noticeable the further apart east-west they are. Think of longitude lines - they are not parallel.
>
Forgive me for being forward, I disagree about some of the above:
I believe 'convergence', or mapping angle is the difference between grid and geodetic north, not divergence. Convergence will change with not only east-west differences, but north-south differences as well.
Imagine that geodetic north is directed to north pole, it is the meridian, anywhere you are. Grid north is a single north direction, defined in the projection plane's nomenclature. there is only one meridian passing through the projection plane. i believe VanSickle illustrated this better than i can describe it. take a Lambert for example; one station 2 miles west of meridian compared to another station 2 miles east of meridian, both stations at the same northing, will yield equal, but opposite convergence.
now take one station 2 miles west of the meridian compared to another station two miles east of the meridian, but the two stations also have a 10 mile difference in their northing. the convergence will not be equal and opposite for the two stations
I also believe LaPlace corrections involve deflection of the vertical corrections, not grid projections.
> All the pc surveying software that I know about has a feature to reduce the coordinate file to grid or vice/versa. Simple fix.
John,
I have never seen a data collector that automatically converts grid coordinates to ground coordinates. Instead they will display grid or ground distances based on the combined factors at each end. If you want to reduce the coordinates to grid you need to perform a localization or what ever your manufacture calls it. If you do not apply a localization then the out put coordinates are still on the grid.
> I have never seen a data collector that automatically converts grid coordinates to ground coordinates. Instead they will display grid or ground distances based on the combined factors at each end. If you want to reduce the coordinates to grid you need to perform a localization or what ever your manufacture calls it. If you do not apply a localization then the out put coordinates are still on the grid.
Survey Controller will do just that. I do it all the time on TxDot jobs without doing a calibration. I wouldn't call it "automatically", you must have the settings right.
James
Grid vs. Ground in RTK data collector?
:good:
😀
:popcorn:
Mock Post
there are many variables here,
What DC do you use? What software? Go to your job and under settings where you found that grid was checked, write down everything you can find about the coordinate system and post it here, including the scale factor. There is a way to fix this. but we have to know more info.
does Colorado require all distances to be given in ground or is grid acceptable?
Yes, set-up the job, projected to a coordinate system, either given to you with metadata, or one of your choosing.
My data collector will allow you to input either a modified surface system in a state coordinate system taken to "surface" or a transverse mercator system set to a chosen elevation to simulate ground distances.
I think doing a "localization" also projects a coordinate system, probably transverse mercator, but I don't use those units, and wouldn't do that anyway.