Long time lurker first post. No license just a 25 year button pusher who has been with same company the entire time. I've learned many things from this forum and honestly some of the technical GPS discussions get way over my head. I've read so many different takes on this I figured it was time to ask and see what people a lot smarter than me say.
For example we are the consulting engineers for a new sewage treatment plant. The entire job site is probably only 600' X 300'. What I typically do on any new job is use Trimble VRS to establish SPC on the point I will set base up on. After initial VRS everything is done base Rover.
On this job and every construction job the contractor will set 4 points boxing the job site in and then we will use base Rover and shoot contractors points for Horizontal then run levels for vertical. We give these coords to contractor and they localize to these 4 points.
So on small job sites what is the proper way to do things. Use one point every time like I do or localize to 4 points.
Construction sites being what they are it is a great advantage to be able to set up wherever is convenient on any given day. IMO localizing should be done with a minimum of 3 points and having 4 leaves them with a spare.
Rtk is typically accurate to + - 0.05' Horiz, and 3x that, vertically with older gear.
You already know that.
That will be good for alot of the project.
But not for other parts.
N
Our Carlson Rep. says to use 4-5 points, 4 on the outside and one in the middle of the project.
7cy1mvp, post: 372834, member: 11726 wrote: Long time lurker first post. No license just a 25 year button pusher who has been with same company the entire time. I've learned many things from this forum and honestly some of the technical GPS discussions get way over my head. I've read so many different takes on this I figured it was time to ask and see what people a lot smarter than me say.
For example we are the consulting engineers for a new sewage treatment plant. The entire job site is probably only 600' X 300'. What I typically do on any new job is use Trimble VRS to establish SPC on the point I will set base up on. After initial VRS everything is done base Rover.
On this job and every construction job the contractor will set 4 points boxing the job site in and then we will use base Rover and shoot contractors points for Horizontal then run levels for vertical. We give these coords to contractor and they localize to these 4 points.
So on small job sites what is the proper way to do things. Use one point every time like I do or localize to 4 points.
are you using SPC coordinates for everything? It's about .3' in 1000' here, so it's not a good idea for construction.
I guess I'm a little confused as to why a localization would be necessary if you're working in pure State Plane coordinates.
Just because I'm paranoid, doesn't mean they aren't out to get me.
7cy1mvp, post: 372834, member: 11726 wrote: Long time lurker first post. No license just a 25 year button pusher who has been with same company the entire time. I've learned many things from this forum and honestly some of the technical GPS discussions get way over my head. I've read so many different takes on this I figured it was time to ask and see what people a lot smarter than me say.
For example we are the consulting engineers for a new sewage treatment plant. The entire job site is probably only 600' X 300'. What I typically do on any new job is use Trimble VRS to establish SPC on the point I will set base up on. After initial VRS everything is done base Rover.
On this job and every construction job the contractor will set 4 points boxing the job site in and then we will use base Rover and shoot contractors points for Horizontal then run levels for vertical. We give these coords to contractor and they localize to these 4 points.
So on small job sites what is the proper way to do things. Use one point every time like I do or localize to 4 points.
On Small Jobs, bring your control in with VRS, then adjust it and make it work, then leave the GPS in the truck and get the robot or total station out.
Never do layout work with GPS.
Kris Morgan, post: 372965, member: 29 wrote: On Small Jobs, bring your control in with VRS, then adjust it and make it work, then leave the GPS in the truck and get the robot or total station out.
Never do layout work with GPS.
We do most of our layout work with GPS. Sure, when things need to be really tight we'll pull out the robot and/or level but for 75% of our work we lay stakes out with GPS and have had little to no issues. We did two sewage treatment ponds last year, all GPS, came out just fine.
WA-ID Surveyor, post: 372973, member: 6294 wrote: We do most of our layout work with GPS. Sure, when things need to be really tight we'll pull out the robot and/or level but for 75% of our work we lay stakes out with GPS and have had little to no issues. We did two sewage treatment ponds last year, all GPS, came out just fine.
The last sewer job I worked on had a .1% grade. No way GPS would have flown on that baby. 🙂
Kris Morgan, post: 372994, member: 29 wrote: The last sewer job I worked on had a .1% grade. No way GPS would have flown on that baby. 🙂
Or Flowed!
B-)
Loyal, post: 373006, member: 228 wrote: Or Flowed!
B-)
Just went back and checked and it was 0.7' over 500' or 0.14% of flow. Nearly flat. 🙂
Williwaw, post: 372957, member: 7066 wrote: I guess I'm a little confused as to why a localization would be necessary if you're working in pure State Plane coordinates.
Actually, I don't ever localize when I'm in control of setting up the coordinates, state plane, modified state plane, local system, there just isn't a compelling reason to do it. And if it's a state agency like DOT they often give me a control sheet and there is no reason to calibrate that either.
Much better to set up the projection and use a Geoid Model, hold the leveled elevations.
I don't understand why there is so much calibration going on with the newer Geoid models available. It's so 1990's
And for tight building control the robot can't be beat:-)
Kris Morgan, post: 373108, member: 29 wrote: Just went back and checked and it was 0.7' over 500' or 0.14% of flow. Nearly flat. 🙂
I'm guessing it's at the end of a long "run" lots of "flow" pushing it along?
I've taken a new job this spring and earlier this week I returned to a site to re-topo, with robot, a stretch of curb and sidewalk my predecessor had topo'd with GPS. The differences in elevation range from about a match to 0.4' difference.
7cy1mvp, post: 372834, member: 11726 wrote:
On this job and every construction job the contractor will set 4 points boxing the job site in and then we will use base Rover and shoot contractors points for Horizontal then run levels for vertical. We give these coords to contractor and they localize to these 4 points.
So on small job sites what is the proper way to do things. Use one point every time like I do or localize to 4 points.
I'd prefer to use the 1 point, and it will give better answers, but after localising with 4 points it'd probably make little actual difference as long as the localisation shots were reliable.
I know it wasn't an option in your question, but, obviously a good total station will murder the GPS for accuracy on such a small site. So, I'd use neither of the GPS options.
On a site that small, I would set two points with GPS spaced as far apart as feasible. Shoot the baseline distance with the gun. Hold the SPC bearing from GPS and the distance generated from the gun. Modify coordinates. Hold GPS derived elevation on one point. Locate other control points with the gun.
I think a localization on a site that small will contain more error and it won't be that much of a time saver.
Thanks for responses. Nothing critical will be done with GPS. Horizontal maybe but all vertical will be level or robot. This job was just an example of how all contractors do things around here.
I agree with poster above if the coords we give the contractor are SPC then there is no need to localize it's pointless but convincing a contractor of this is another story.
My main question is SPC or not is there any advantage on small site to surround job with additional points and localize. I've debated with contractors so many times over this but my knowledge isn't enough to convince them it's unnecessary on small jobs. They just do things the way their equipment salesman told them.
What Jim H says is pretty much what I do. I have 3 points that levels were run thru and have good horizontal on. Contractor is responsible for his own staking I just have to check his stakes. I will set up base on same point every time for the entire job.
I've tried convincing contractors that with SPC there is no need to surround job and localize but they just look at me like I'm crazy.
Anyway thanks for everyone's time sorry if I'm not explaining clear enough. Just looking for verification of what I already know.
Conrad, post: 373118, member: 6642 wrote: I know it wasn't an option in your question, but, obviously a good total station will murder the GPS for accuracy on such a small site. So, I'd use neither of the GPS options.
The voice of real wisdom.
GPS will be used for the dirt work. All structures will be done with level and robot. My question is for any job. This job just happens to be the most recent this has come up on. Trust me I'm well aware of vertical inaccuracies with GPS.
7cy1mvp, post: 373237, member: 11726 wrote: GPS will be used for the dirt work. All structures will be done with level and robot. My question is for any job.
your original question didn't make this clear. actually your question was specifically regarding small job sites...
7cy1mvp, post: 372834, member: 11726 wrote: So on small job sites what is the proper way to do things [?]
:totalstation:
...Use one point every time like I do or localize to 4 points.
so, if we chose to use the GPS then your single base will be the method of choice as it will contain none of the small (and possibly unwanted) rotation, scale and translation inaccuracies introduced into your localised coordinate system by the 'imperfect' measurements (relatively speaking) made to your control points.