I'd be interested to know how many man hrs you bid. By your question you're not sure what it takes to achieve 4 ppm work. So, 4 ppm man hrs might catch you under budget, field and office.
R.J. Schneider, post: 409120, member: 409 wrote: Meant the <2mm, not the 0.0005' Paul mentioned.
0.002m = 0.0065' for final precision. I said you need 0.0005' agreement testing prisms for distance. After a full analysis, something I would not do for free, my budget for that may end up being 0.001'. With the setup, instrument and pointing errors those seemingly small numbers add up.
I do not plan on doing anything of that precision with what equipment I currently have. I personally test and adjust my whole range of prisms to be under 0.004' for distance, Topcon cans, tilting prism setups, regular size and peanut and a peanut on a plumb line. All except the peanut on plumb line on a tribrach adaptor on the same tribrach. That occurs after I check and set all triprachs and plummets over a point. Then I recheck the prisms on the other tribrachs I use under my instrument. For purposes of your work you would always want the same prism, tribrach adaptor and tribrach to remain as a set.
Also for his quality of work you may want to consider instrument pedestals, not tripods over pins in the ground.
Paul in PA
Paul in PA, post: 409148, member: 236 wrote: 0.002m = 0.0065' for final precision. I said you need 0.0005' agreement testing prisms for distance.
I wouldn't be able to distinguish the 0.0005' worth of centering error using an optical plummet. The http://www.leica-geosystems.us/downloads123/zz/tps/Viva%20TS15/brochures-datasheet/Leica%20Viva%20TS15%20Datasheet_us.pdf&apos ;">instrument the OP mentions already has an estimated +/- 1mm - 1.5ppm standard accuracy with a gpr1 prism (which itself has a stated accuracy of 1mm), inherent in the process.
It's possible you could achieve the <2mm between the intervisible points in the secondary control network.
rfc, post: 409062, member: 8882 wrote: Thinking "outside the box"...
Can you see any of the primary control or any of the new points from the top of the "permanent structures"? If so are they solid enough for a setup?
I wish, Most are C-Cans and Tents.
R.J. Schneider, post: 409160, member: 409 wrote: I wouldn't be able to distinguish the 0.0005' worth of centering error using an optical plummet. The http://www.leica-geosystems.us/downloads123/zz/tps/Viva%20TS15/brochures-datasheet/Leica%20Viva%20TS15%20Datasheet_us.pdf&apos ;">instrument the OP mentions already has an estimated +/- 1mm - 1.5ppm standard accuracy with a gpr1 prism (which itself has a stated accuracy of 1mm), inherent in the process.
It's possible you could achieve the <2mm between the intervisible points in the secondary control network.
The 0.0005' is prism distance only, replacing the prism setups on a tripod adaptor without moving the adaptor. That is the centering remains the same for all prisms in a test. The point is to separate the distance error from other errors so you can better analyze your work. Instrument measuring distance is a separate error.
Paul in PA
someone here has suggested to me to just do a GNSS Site Calibration using 4-5 of the existing Primary Control Points to create a new scale factor and coord system to use going forward on the job(Theory: "That all new points should just be rotated and scaled to that job anyways").
But might that provide me with different issues? (Seems like an easy way out as I have adjustment software) I feel it's not quite the same quality of coordinates as static control surveys would provide and I'm going to need to adjust the points that I create from these anyways so better to have points you trust eh?
Anyway you slice it: distance and tribrachs is the whole enchilada.
I'd use 2 instruments (T1, T16) set 90å¡ apart and 8 ft away from a target setup. Transit the scope to place the wedge target over the point. I'd use a precise target with a long vial, not bull's eye level. The only way I know how to be sub mm, and no surprises. If you're working 10-12 points, it won't kill you.
Triangulate the net to as high a reliability as possible. No forced centering. Sub second.
Adjust. Then compare to existing control. And check with client. Maybe the existing control isn't as good as client thinks it is. Or it's a scale that is required, good or bad.
Q: what is the site? How many points?
IMO
What is the specified accuracy for placing the new control system relative to the old one? I was assuming that to be nominal, an ordinary survey project that might be handled with a traverse or GNSS. I can see that you should tie into the same system, but if it wasn't done to the same accuracy that your new points need, then you can't let it warp your new results, just translate and rotate, or depending on the physical configuration maybe hold three distances from the old points to the new ones in a way that will not distort the new part of the network.
I'm surprised you mention getting a new scale factor. What coordinate system is used for the project that needs the 2 mm spec? Are those horizontal distances at ground elevation or something else? A scale factor derived from the old system may not be accurate enough for your new work.
Isn't it only the new system that needs the 2 mm specification for all and only points relative to each other within that new portion? That is an extraordinary project.
And I'm still waiting to hear how the client interprets the 2 mm spec.
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A problem well stated is problem half-solved. ~Charles Kettering
Bill93, post: 409177, member: 87 wrote: What is the specified accuracy for placing the new control system relative to the old one? I was assuming that to be nominal, an ordinary survey project that might be handled with a traverse or GNSS. I can see that you should tie into the same system, but if it wasn't done to the same accuracy that your new points need, then you can't let it warp your new results, just translate and rotate, or depending on the physical configuration maybe hold three distances from the old points to the new ones in a way that will not distort the new part of the network.
I'm surprised you mention getting a new scale factor. What coordinate system is used for the project that needs the 2 mm spec? Are those horizontal distances at ground elevation or something else? A scale factor derived from the old system may not be accurate enough for your new work.
Isn't it only the new system that needs the 2 mm specification for all and only points relative to each other within that new portion? That is an extraordinary project.
And I'm still waiting to hear how the client interprets the 2 mm spec.
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A problem well stated is problem half-solved. ~Charles Kettering
Spec like that is either very serious, or just something that came off a cad drawing. Question remains.
Last time I saw a spec like that it was a dam subsidence survey.
mrewenmacdonald, post: 409166, member: 11707 wrote: someone here has suggested to me to just do a GNSS Site Calibration using 4-5 of the existing Primary Control Points to create a new scale factor and coord system to use going forward on the job(Theory: "That all new points should just be rotated and scaled to that job anyways").
But might that provide me with different issues? (Seems like an easy way out as I have adjustment software) I feel it's not quite the same quality of coordinates as static control surveys would provide and I'm going to need to adjust the points that I create from these anyways so better to have points you trust eh?
Can you even just approximately sketch your control point positions and the sight lines you have in your network? A pre-analysis with some input deviations will show up what you are likely to be able to achieve, and the required observational quality needed to achieve your spec.
Can you tell us what confidence is specified, if any, with the tolerances? Also, who will be using the control that will be able to tell whether you achieved the 2mm relative accuracy?
Paul in PA, post: 409065, member: 236 wrote: How good is the primary control?
Primary Control is not great, Just running some checks I found errors of 10mm on one backsight and between Points on the other side of the river So not sure what I'm going to do there.
Paul in PA, post: 409065, member: 236 wrote: Where is it relative to the project site?
Lots of Primary Control Points to the South, SouthWest and NorthWest but nothing to the East.
Paul in PA, post: 409065, member: 236 wrote: Can you set on a primary control point and observe more than one project control point?
Unfortunately from each station I can see 2 points (they were traversed in) but very few of those points see into the area which I need to place control points.
Paul in PA, post: 409065, member: 236 wrote: How many new site control points do you have?
I have drilled / pounded 4 pieces of 1" rebar surrounding the bridge. (They are frozen into the ground until April most likely when they will move)
Paul in PA, post: 409065, member: 236 wrote: How many site control points can be observed from more than two other SCPs?
I have set up the secondary points to be able to see at least 2 others and from 2 SCPs you can see 3 others.
Larry Scott, post: 409107, member: 8766 wrote: I can't imagine holding existing control if the key element is very high relative accuracy. One X Y, one azimuth. Relating to existing control may impart scale and distortion. Is the control known to be 1:250,000?
This brings up a different problem. with a scale factor like they have provided me: 0.99976456 provides me with quite a lot of scaling but as this project is butting up to 2 different projects on either side on very tight tolerances (A tunnel to the north, and Elevated Guideway for a Tram to the south) I don't know how much I can really vary from this primary control as I haven't been able to talk with these other surveyors yet and they'll be coming off of the same control to create their own secondary control (Really messed up to have 3 different secondary control networks right next to each other on such tight precisions but that's something they don't understand)
mrewenmacdonald, post: 409235, member: 11707 wrote: This brings up a different problem. with a scale factor like they have provided me: 0.99976456 provides me with quite a lot of scaling but as this project is butting up to 2 different projects on either side on very tight tolerances (A tunnel to the north, and Elevated Guideway for a Tram to the south) I don't know how much I can really vary from this primary control as I haven't been able to talk with these other surveyors yet and they'll be coming off of the same control to create their own secondary control (Really messed up to have 3 different secondary control networks right next to each other on such tight precisions but that's something they don't understand)
Is the 10 mm 'error' in the distance check in grid v ground distance? I assume that 0.99976456 is combo factor. Did you apply that to your check distance?
So I'd still create a closed network of your own triangulation and distance, average elevation. Adjust it to determine the integrity of your own closed figure. Establish a closed net with as much redundancy (triangulation) as possible. This is what starnet is all about.
Then a second readjustment holding existing control as necessary to 'fit' in with the overall project. The combined scale may not be large, due to the elevation factor. And even holding their multiple control points, I'd hold them tight but not fixed. There might be a few that are superior, and one or two marginal. After figuring out what's good and what's critical, hold the good ones. Best fitting control is the enchilada.
Double and triple check EDM/mirror/tribrach pairs. And use only a finite set. Trusting tribrach at 0.01' is hazardous, as others have pointed out. Precise targets, wood tripods: no staking poles. Least square adjustment is an absolute. I hope your familiar with something like starnet. I built a bridge/tunnel a long time ago. It was a challenge, but I had an advantage of no foreign control.
So, what is the zone, and average elevation?
It'll work. Just check, check, and recheck.
IMO.
Be very mindful of grid distances versus ground distances. Mix that up, and good looks bad, and vice versa.
So you are building a bridge. Are the bridge plans in ground distances? The talk about scale factors is scary when something has to fit on the ground, not on a grid.
Bill93, post: 409253, member: 87 wrote: So you are building a bridge. Are the bridge plans in ground distances? The talk about scale factors is scary when something has to fit on the ground, not on a grid.
Projects like these that I've seen, often have:
State supplied control in SPC, and engineering control in ground coordinate system. I can't imagine getting into the building phase with only SPC cords on everything. But, that's what the profession is all about: knowing the difference, and acting accordingly.
Unfortunately, there are two goals: a) meet the client's needs, b) make sure that any cost extras in construction due to survey isn't your mistake.
.999764...... scale factor indicates a site at elevation or there is a large grid value.
Call it .23 in 1000-feet or meters. That is a healthy scale that needs to be dealt with, no doubt there are some project design coordinates that are on the surface already, the problem with older control is that you can't really change it, you are stuck with it because everything is designed and probably bid out so you have to make it work, if there are some outliers they need to be identified and dealt with. 2mm sounds like someone in an office dreamed that up, you already suspect there is 10mm in the primary control (that isn't terrible by the way); I would do a report on the primary control first and sit down and get the 2mm adjusted to something more realistic if possible, cause 2mm ain't happening with the other control; unless they only want you to kinda get it in the primary and hold a little patch of "good" control adjusted to itself.
Generally control surveys are done in SPC, then "adjusted" somehow to project coordinates, I would do the control in SPC.
If you really have to get to 2mm and you do it conventionally it's best to be done at night and it's important that the actual point can be observed when you turn angles. By that I mean when looking through the scope you can see the ground and a point sitting in the punch mark. Then careful distance measurements taken to a glass with a well adjusted tribrach and spin it to take out any possible issues.
If you do it with GPS? I know it's probably not helpful but I would want R-10's even if I have to rent some.
Well adjusted tribrachs, spin them anyway, get lots of redundant measurements, and let the least squares program tell you what you get, you won't be able to constrain it outside the 300x500 area and get the 2mm; that is a given with the primary control not up to the standard.
You don't mention if this is 3d, is the 2mm also for elevations? That is a whole nuther issue, particularly with a river running through the site.
Finally keep really good reports on your adjustments, procedures, take pictures, write notes, take times and temp, pressures, identify all the equipment used, ect.....; no one will ever find that you are within the 2mm when they go and set up, they will always have something to squawk about; it needs to be "proven" using your actual data and records.
I did work with a company that set permanent control points on pillars, they were set deep in the ground and protected, a mount point projected out of the top. Something like that would be helpful to achieve the 2mm standard and they wouldn't move through the project life if set in "good" quiet spots like the ones I used were.
MightyMoe, post: 409257, member: 700 wrote: .999764...... scale factor indicates a site at elevation or there is a large grid value.
Call it .23 in 1000-feet or meters. That is a healthy scale that needs to be dealt with, no doubt there are some project design coordinates that are on the surface already, the problem with older control is that you can't really change it, you are stuck with it because everything is designed and probably bid out so you have to make it work, if there are some outliers they need to be identified and dealt with. 2mm sounds like someone in an office dreamed that up, you already suspect there is 10mm in the primary control (that isn't terrible by the way); I would do a report on the primary control first and sit down and get the 2mm adjusted to something more realistic if possible, cause 2mm ain't happening with the other control; unless they only want you to kinda get it in the primary and hold a little patch of "good" control adjusted to itself.
Generally control surveys are done in SPC, then "adjusted" somehow to project coordinates, I would do the control in SPC.
If you really have to get to 2mm and you do it conventionally it's best to be done at night and it's important that the actual point can be observed when you turn angles. By that I mean when looking through the scope you can see the ground and a point sitting in the punch mark. Then careful distance measurements taken to a glass with a well adjusted tribrach and spin it to take out any possible issues.
If you do it with GPS? I know it's probably not helpful but I would want R-10's even if I have to rent some.
Well adjusted tribrachs, spin them anyway, get lots of redundant measurements, and let the least squares program tell you what you get, you won't be able to constrain it outside the 300x500 area and get the 2mm; that is a given with the primary control not up to the standard.You don't mention if this is 3d, is the 2mm also for elevations? That is a whole nuther issue, particularly with a river running through the site.
Finally keep really good reports on your adjustments, procedures, take pictures, write notes, take times and temp, pressures, identify all the equipment used, ect.....; no one will ever find that you are within the 2mm when they go and set up, they will always have something to squawk about; it needs to be "proven" using your actual data and records.
I did work with a company that set permanent control points on pillars, they were set deep in the ground and protected, a mount point projected out of the top. Something like that would be helpful to achieve the 2mm standard and they wouldn't move through the project life if set in "good" quiet spots like the ones I used were.
Tunnel, tram, bridge? This probably ain't sea level.
Bill93, post: 409177, member: 87 wrote: I'm surprised you mention getting a new scale factor. What coordinate system is used for the project that needs the 2 mm spec? Are those horizontal distances at ground elevation or something else? A scale factor derived from the old system may not be accurate enough for your new work.
The bridge dimensions are grid dimensions on the mapping plane and not ground dimensions. I'm dealing with a variant of a Mercator Projection Called 3TM here in Alberta (So no State plane Coords here but I'm assuming that's the same kind of beast), But I only plan to rotate my grid coordinate system to the primary control and then only use it for checks down the road, perhaps if anything starts moving on me.
Bill93, post: 409177, member: 87 wrote: And I'm still waiting to hear how the client interprets the 2 mm spec.
I don't doubt that they need such precision as they are building this bridge from both ends to meet in the middle and there will be other survey contractors with whatever means necessary available to check my work.