Hello to all,
I have already been learning much from some of the surveyors in this forum by searching and reading others' posts. There is so much knowledge hiding in your brains out there.
We recently received a staking request from a company and the only thing they can provide us is the UTM coordinates (in International Feet) of the points they want staked.
Typically, (including jobs we have done for this same company in the past) we would receive a DWG, building plans, or at a minimum, a map with some known points to tie to the project. This engineer we are talking to has informed us that all they ever send surveyors is the UTM coordinates, and the surveyors are able just go out and stake the points.
Further more, they cannot provide any information about a vertical datum or benchmark. Though the points all have elevations on them, no details about how they are derived can be provided by this engineer.
The only thing they were able to send us (besides a PDF of a table with the Easting, Northing, and Elevation of the points) was the engineers project file which is just an XYZ file with 3 MILLION POINTS! Even to convert the points to ASCII format with descriptions attached (none of them noting any control type monuments or points), it took about 12 hours.
Are we missing something? Our concern here is the level of accuracy we can attain by just setting up, telling our GPS we are in UTM 10 North, tying a known UTM point nearby (2 miles away from the project is 1 NGS Benchmark adjusted vertically to NAVD88 and horizontally to UTM/SPC within thousandths of a meter), doing a static observation on the other end and send it to OPUS to have a point on either side of the project, and then stake away using the coordinates they provided.
We don't use the network. We only use base and rover RTK setups. Is this the problem? When we do staking for clients that require using SPC, we use the control they provide to localize on their datum and measure everything in ground distances, after ensuring we will match any existing infrastructure. We set control and then mostly use our total station to layout with high precision and accuracy.
We would love to do the work, but at this point we have declined to do the job, unless they can provide us with some type of known points to tie to, including a vertical benchmark...
Any insight would be greatly appreciated.
Cheers!
I may look like an average American male, but I will surprise you.
If you think you have a good chance being hired for the work, why not write up a contract specifying in DETAIL the methods you will use, the precision you will achieve and the assumptions you are being forced to make about the data provided by the client?
"The points to be staked are relative to the UTM horizontal coordinate system, Zone __ and are assumed to be relative to the NAD83 elevation datum. The CLIENT must notify the SURVEYOR prior to commencement of field work if staking of the given point elevations is to be done relative to any other datum. If the surveyor is notified to use a different datum after staking has commenced, an additional fee based on the following schedule will be paid by the client..." Make the additional fee high enough that it might motivate the engineer to provide the information you need, or that he will be held to account by his company if they get hit with it later.
The coordinate system is a red herring. Your issue is a lack of control as it relates to the project at hand. Depending on the needs of the project, this might not be as big of an issue. The relative accuracy of the points you end up laying out will be determined by the precision of the field methods you employ. Your issue will be absolute accuracy, where your layout falls in comparison to where the engineer planned. This is a big problem if features tie into existing features but might not be so much of a problem for laying out something like wells. The question you need to ask the engineer is ‘how critical is the actual location in relation to the surrounding environment?’.
From your comment on 3 million points, it sounds like the project was designed based on LiDAR or point cloud data of some sort. Chances are the data was tied to a post processed trajectory and not an autonomous position so any absolute control you come off will be at least close.
As for you proposed field method, if you are just going to base your control on OPUS, then why bother with the NGS passive mark? OPUS is great to get you close but the discrepancy in accuracy between it and the passive mark will just drive you crazy. I would recommend using the mark as a base or at least use it as a base from which to set a secondary control point on site.
*** Apparently Peter beat me to the point.