I'm working on a hydro dam project - the job is in UTM. The control drawing in the plans clearly states Grid Coordinates and gives a combined scale factor (0.9996445) to convert grid distances to ground.
There are numerous structures to be built, anchor bolt patterns to be laid out. The dimensions of these are clearly the actual distances required - the ground distances, not the grid distances.
If my math is correct, that's close to 40mm per 100m difference.
The head surveyor says each structure is independent, nothing is more than 30 or 40 metres long, work in grid and don't worry about it.
Okaay...
I ran into this before on a bridge - in MTM this time, so less difference, but it was 120m long from Workpoint 1 to workpoint 4 on the plans, but inversing between the coordinates for those workpoints came to 121.016m. In this case no one had a clue what I was mumbling about and the bridge still fitted together and we all went home happy - I'm sure I'm going to keep running into this and was wondering what others have to say on the matter.
Thanks
and gives a combined scale factor (0.9996445) to convert grid distances to ground.
That equals 0.36' in 1000 feet. Or, 0.36 M in 1000 meters.
Also, if you get SMALLER from grid to ground, then your GRID is above ground.
IF there ever was a need in continuing education, it would be in State Plane Coords, and their practical use.
I am not the brightest bulb on the subject, but some things seem obvious.
Anybody else that chimes in, would you please recommend a book the could be called SPC for dummies, or "The practical use of State Plane Coordinates".
I should read it.
Thanks!
Nate
You can probable find it somewhere else, but this was the first site google sent me to
And besides, the DC software should handle this for you so there's really no reason to ignore it.
We had a job, I had delegated it to my partner (also an LS). Check the backsight, 0.07', hmm, I said are those grid coordinates? He says yeah, I think you're right, let me look up the CF. I said there is no need, we'll just pick the Spc And zone from the list. Recheck, BS nearly flat :-). Easy.
In structures there are usually some tolerances that can allow the addition of a washer or spacer to make it all work on the ground. If the project is small enough or the separation between Grid and Ground is small enough, the structures can be built without incident. Just stake out as designed and let the construction guys work out the details. Of course I would have the RFI’s to cover the fact that you tried to explain what may happen.
We had a project at 4400 feet above sea level with lots of drainage structures that was over 10 miles long. Many of the pipe runs were 400 feet long (and at minimum grade). The RFI asked which they wanted to hold; elevations or slope? The answer was of course they would hold both of them! So our next RFI suggested that we could move the structure so that the pipe length would remain at 400 feet which would hold both the elevation and the slope. Not an option. I have not mentioned the many conversations back and forth as we tried to inform the engineers and the inspectors why this was necessary. Our final suggestion was to stake out everything at grid raised to ground, holding the elevations as designed with the understanding that the inspectors and as-builts would reflect ground information which was below minimum slope for some of the pipes and pavement. There were some hiccups as it went together, but it got built without too much more effort than normal.
As more jobs are mapped at Grid, more projects will be designed at Grid with the stakeout having to be accomplished at Ground. Lots of BIM is now including the civil design and will continue to place the burden of what to do on the surveyor. The surveyor better have it all worked out with designers, construction and inspectors before starting on the project!
This white paper has been around for years. I still hand out copies to engineers, project managers and other surveyors who are having trouble with the concept of grid versus ground coordinates.
Yes I have that white paper - It is excellent. He details this exact problem, where the plans are in Grid, the workpoints are in Grid but the dimensions are in Ground.
I wouldn't criticize any engineer or architect for not understanding the issue - it's hard enough for surveyors to understand - but as noted above it becomes a difficult problem to deal with, when the powers that be don't even realize/understand there is a problem.
UTM In Thunder Bay ?
I would only use it to find the job site.
if all these independent structure are to be eventually connected I would hesitate to use UTM for stakeout.
Paul in PA
UTM In Thunder Bay ?
Well it's in White River, 4 hours east (same place you helped me with the static!) Biggest construction company in the world, apparently - Daragados from Spain, so they must know what they're doing right?
I don't think UTM/MTM/State Plane is suitable for civil engineering projects but I have to do what I'm told!
UTM In Thunder Bay ?
> Well it's in White River, 4 hours east (same place you helped me with the static!) Biggest construction company in the world, apparently - Daragados from Spain, so they must know what they're doing right?
> I don't think UTM/MTM/State Plane is suitable for civil engineering projects but I have to do what I'm told!
On these projects, what I have often seen in the past is a mix of grid (control by the land surveying company) and ground (civil/structural).
The main thing is to make sure that your infrastructure data is actually prepared at grid level. Which means that your CAD distance for a 40m polyline between two points will actually be 39.984m; assuming a scale factor of 0.9996, I forgot the exact number you mentioned.
I like to SF 1.0000000 myself for structural. We always end up sharing CAD files and it is a lot easier to be at ground than grid in those situations.
UTM In Thunder Bay ?
Sorry.
That was too much of a distraction and I decided to erase the comment.
UTM In Thunder Bay ?
I don't think UTM/MTM/State Plane is suitable for civil engineering projects but I have to do what I'm told!
I must agree with that!!!!
Wonder who thought UTM grid was a good idea for construction?
It's more for large mapping work. To make a nice picture.
UTM In Thunder Bay ?
> On these projects, what I have often seen in the past is a mix of grid (control by the land surveying company) and ground (civil/structural).
Yes, but in your experience is this mix acknowledged and recorded as such in the notes, or are the engineers/architects not realizing that there is an issue?
>
> I like to SF 1.0000000 myself for structural. We always end up sharing CAD files and it is a lot easier to be at ground than grid in those situations.
My issue is that the workpoint coordinates are grid coordinates so inversing between them gives a slightly different length to what the dimensions on the plan shows.
My feeling is the workpoints have to be adjusted to ground, but I'm not in charge...
Three Words:
Low Distortion Projection
> Three Words:
>
> Low Distortion Projection
I agree but impossible to sell, now and in 20 years. The engineers are already overwhelmed with the basic UTM projection.
UTM In Thunder Bay ?
> My issue is that the workpoint coordinates are grid coordinates so inversing between them gives a slightly different length to what the dimensions on the plan shows.
> My feeling is the workpoints have to be adjusted to ground, but I'm not in charge...
I am thinking you are using a total station for this work. Your control is grid. How about your layout data; grid or ground? If ground, then it should be fairly simple to explain to the chiefs.
Not impossible. you just have to take time to educate the engineers you work with. I have been utilizing low distortion systems for the last 15 years. From an engineering stand point it is much simpler for them to understand. In fact, Oregon now has 20 such system defined in statute and the push came from our DOT.
:good:
UTM In Thunder Bay ?
Had a similar experience with a U.S. Army Corps of Engineers flood control project nearly twenty years ago. Surveying contract was to add to existing control, establish existing boundaries, required easement corners and locate utilities. Everything was to be in 3D CAD (MicroStation) files. Control, property boundary and utility location was all at Grid x,y coordinates. Storm/sanitary structures and flowlines at actual elevation. Aerial mapping CAD files provided to us were also 3D and at real world elevation. Field located manholes and aerial mapped structures fit well in 3D throughout the project. All drawings required coordinate system and project scale factor stated in title block.
The saving grace was the all lines showing distances were required to be labeled with both ground and grid distances. The design portion of the project was split between several engineering firms. I got a few calls asking which of the two distances was correct. The discussion of grid versus ground happened BEFORE design started.
Another reason flood control projects and dams are designed in such systems is to fit with existing large area mapping. Calculation of water travel times between structures miles apart are needed to calculate the timed release of water.
Metro White River Surveying
Colin-
As a matter of interest, I believe my grandfather, W. S. Gibson OLS surveyed in White River in the winter circa 1900 out of a tent.
He was a fine man and brought me into the profession when I was 5 (over 60 years ago) by having me hold the end of the chain up to new foundations.
Cheers,
Derek
