Close enough to find an iron pipe.
There is control points on Mount Everest? You got a cross tie for that point?
I agree with the 0.20 foot number, but like so many others have said, you might get all sorts of screwy answers.
nice coords..
great sthick.
The reason for my question
Not sure what you mean by coordinate. Do you mean there are coordinates stated on some plat with no reference beyond "this is a state plane coordinate", because without a reference then the next guy isn't going to get very close.
Means to locate a point in a state plane system have been around for a while. You certainly don't need to use GPS. I was running state plane control back in the 70's and changed from 27 to 83 coordinates in the early 90's all before I started using GPS.
I can't imagine someone just taking a coordinate and puking an OPUS solution out and using that to set corners. My experience with that is I give a firm coordinates tied to HARN points and 1st order bench marks in the area using GPS static in the late 90’s. The firm sets up on a new control point and proceeds to throw out an OPUS solution in 2010(because OPUS is sooo much better). Now their work is .4’ off horizontally and .7’ vertically-all because they didn’t want to travel to control points and used a new Geoid model without adjusting to the bench marks. This situation has happened more than one time.
So, I don’t think coordinates without site control works worth a c#$p.
With site control you should be good (but you should still retie controlling corners) but that is irrespective of GPS. You don't have to drag GPS out.
The CORS network is in constant flux. It moves and shifts and those "velocities" are going to impact coordinates over time. Without really good metadata to "track" that movement, using it to reset coordinates is very suspect.
The reason for my question
>My experience with that is I give a firm coordinates tied to HARN points and 1st order bench marks in the area using GPS static in the late 90’s. The firm sets up on a new control point and proceeds to throw out an OPUS solution in 2010(because OPUS is sooo much better). Now their work is .4’ off horizontally and .7’ vertically-all because they didn’t want to travel to control points and used a new Geoid model without adjusting to the bench marks.
Unfortunately happens all the time.
A large international concrete firm wants to expand a plant and hires a respected aerial mapping company to prepare the base map. Said aerial mappers establish a control network on site using a well designed, redundant GPS network tied to HARN stations.
18 months later, once the design is finished, Jackleg, Doofus & Associates are hired to do the construction stake out. They set their RTK base on one control point, get an OPUS solution, hit the other stations with the rover, and then proceed to tell the client that the original control is crap and proceed to readjust everything.
(Of course, you must take into account that the project manager from Jackleg, Doofus & Associates later tells me that the 280 anchor bolts are all f%$ked up because of the contractor; it couldn’t be the stake out because “our initialization was hot”)
The reason for my question
18 months later, once the design is finished, Jackleg, Doofus & Associates are hired to do the construction stake out. They set their RTK base on one control point, get an OPUS solution, hit the other stations with the rover, and then proceed to tell the client that the original control is crap and proceed to readjust everything.
(Of course, you must take into account that the project manager from Jackleg, Doofus & Associates later tells me that the 280 anchor bolts are all f%$ked up because of the contractor; it couldn’t be the stake out because “our initialization was hot”)
Yeah they are soo much better with OPUS than that stupid surveyor who tied in to the local HARN point/points and established bench marks.
Was that "hot initialization" the kind where you "fix" in the parking lot in front of the building, run to the doorway, set the rod down on the on the floor, push the rapid point button and run out before the "fix" is "lost". A great way to get the finished floor. Redesign the whole project from that.;-)
I've a point outside my office that I use for a check every time I make a software or firmware update, or the DOT makes a system or software change.
12-14-12
N...763.978
E....611.192
Elv 849.757
12-15-12
N...763.975
E....611.196
Elv 849.762
1-18-13
N...763.971
E....611.205
Elv 849.743
12-19-10 (same point different gear 2 years ago)
N...763.983
E....611.180
Elv 849.616
The key is knowing your equipment, it's limitations and yours as well.
Plumb bob? What's that?
The reason for my question
> So, I don’t think coordinates without site control works worth a c#$p.
> With site control you should be good (but you should still retie controlling corners) but that is irrespective of GPS. You don't have to drag GPS out.
- What he said, except maybe adding "site control you established or re- measured yourself"
The reason for my question
I'll expand on my comment yesterday.
I shoot the corners each time I go out. That's only good practice.
I suspect some others do too, but maybe I'm naive.
I would not use published (by others) coordinates to set anything.
First, you have to ask if the points you're measuring from are good enough for you.
Then, I'd measure them, picking a technology that would give me the best accuracy. For short work, it may be a TS with good geometry, and for long work, it may be GPS.
There's nothing like a fresh measurement set to let you sleep past 3 AM.
I routinely share point data with the County Surveyor off our HARN network, and the results are always within a few hundreths, sometimes right on. You're getting to rod plumb adjustment accuracy now.
The reason for my question
"Unfortunately happens all the time."
I have seen this so many times it makes me dizzy. I have explained it so many times it makes me dizzier. I explained it to a national firm, who (after 6 weeks of discussion) told me "We don't think we have ever performed a job correctly." E V E R
This is one of several reasons we are moving our profession toward extinction. Some attorney will read a thread like this someday and realize how incompetent many who call themselves "surveyors" are. Someday a judge will listen to this attorney, and at that point our status as "professionals" will cease to exist.
We check ours every morning ...
The reason for my question
I have seen this so many times it makes me dizzy. I have explained it so many times it makes me dizzier. I explained it to a national firm, who (after 6 weeks of discussion) told me "We don't think we have ever performed a job correctly." E V E R
I don't understand what's going on with this. I know that the GPS box is shiny, kicks out important looking numbers and buyers of the equipment have often been sold that it is something it isn't and can't be, but really don't these people check what they do.
It doesn't take long to find that "fix" doesn't always mean "fix", that calibration is often a bad idea, that old cors and new cors coordinates aren't the same, that Geoid 99 and Geoid 09 can be quite different, ect, ect, ect.
The reason for my question
I've actually done this, and found that the prior control was bad - as bad as if it had been done by attorneys ( - all right, that's an exaggeration).
The proper decision path at that point is to determine if the Job Sup is competent. If he is, proceed to step 2.
Step 2: Meet with the Job Sup and share your data with him. It has to be convincing. The two of you will develop a strategy to proceed. I'd likely go off of the existing building (most likely, hedging on purpose here). Why wouldn't you? The floors and steel have to match.
If he isn't competent, you don't want to be on the job. Your firm's name will appear on court documents along with everyone else's.
If proper techniques are used ....
I agree. 0.04' is about right.
I got an interesting one recently, we were following work done by one of the most respected companies in town. They had produced some plans that listed "surface" coordinates for 3 control points, with one at each end of the 2.4 mile project and the third being near the middle. They even included a scale factor of 0.999987xxx. All I think is well and good until I read further where it says "THE SURVEY HEREON HAS BEEN CONVERTED TO SURFACE COORDINATES SCALED ABOUT CONTROL POINT #(the middle point). THE GRID AND SURFACE COORDINATES FOR PT #(middle point)ARE THE SAME". Personally, I would never do this as it would be too easy to mix up surface and grid coordinates, but I digress. Anyways, I set up on the middle point, and after scaling down the two end points from surface to grid, we try to check into them. We miss the north one by 6.5', and the south one by 7.5'. WTF, I am thinking, and go about running static on the three points. After processing, I believe I have come up with what happened. Whomever did the tech work on the project had a little dyslexia, and instead of using the published scale factor of 0.999987xxx, used 0.99897xxx for calculating the surface coordinates of the north and south points (my static session confirmed the coordinates for the middle point). Their field crew then calibrated to these surface coordinates, and went about their survey. As I explained to our client, it was like they were surveying with what they thought was a 100' tape, when in actuality it was only 99.9' long. They had the centerline staked, and I checked between two of their points, which should have been, by stationing, 2412' apart, I measured 2409'. Still waiting to here the fallout from that mess.
The reason for my question
:good:
GPS answers being sought
This is a fascinating thread and will/may continue for some time.
I wrote and posted an item on my web site that asks "with respect to what?"
As a reminder please understand that the GSDM provides local ground level distance and true direction between points with no projection constants, no scale or combined factors, and the GSDM is already in place - just for the using. Check it out.
I'll be happy to provide clarification and answer questions. EFB
Which is it, a few hundredths or a few feet?
In 2009 you did a job using RTK and determined a coordinated for a specific monument. In 2010 you did a different job in the same neighborhood, maybe using the same RTK equipment, or maybe not and determined a coordinate for a different specific monument. In 2011 you did an unrelated job, sent your party chief out to do it with the same or different RTK equipment and he determines a coordinate for a different specific monument in the same neighborhood that is not more than a half mile away from the other two described above. In 2012 another monument is set or found in the same neighborhood and a coordinate determined for it.
Now it's 2013. From your old files you have four monuments, each with a coordinate tied to it. They form something close to a rectangle. You go out with your current RTK equipment and attempt to set new monuments that are at the midpoint between each pair of monuments around the rectangle. You do not revisit the four monuments from 2009-2012.
How close or far will you be to hitting the true midpoint of that straight line in each case? You aren't using anyone else's information. It is your own old data.
Which is it?
Hey, this is about as interesting as the thread I started. "Surveying Under Canopy".;-)
