I performed a topo for a utility company on a vacant piece of land, just woods, fields, and trails (no hard surfaces). Per the scope, I generated 2’ contours and submitted the CAD file including the contours and tin. I wrote out a separate points file with PNEZD to 0.1’.
The design engineer firm asked me for the points to 0.01’. I declined. They’ve since emailed the client requesting the points again, saying that they need them to that precision, in order to do their design. In his email, the engineer states that one of his issues is that when he brings the points in, they don’t fall exactly on the linework. “…the CAD file indicates that the data was collected at a higher precision. The point file sent appears to have been truncated down to tenths. Using this reduced precision is causing the points on the CAD file to be slightly offset from where the feature lines show that they should be.”
I don’t really see how any of this should be a problem to the engineer, and am somewhat amazed that he thinks that he needs it. But I also wonder if I’m just being too stubborn, and should just comply.
I guess that I’m looking for a good way to explain it to the client that given the scope and accuracy requirements, the fact that it’s raw land and not paved surfaces, etc, that 0.1’ is appropriate, and the engineer’s request is excessive and unnecessary. I don’t want it to appear to the client to just be uncooperative.
Tell your client to hire an intelligent engineer [sarcasm]& good luck finding one......[/sarcasm]
It's a software issue of the points and lines not matching. As long as he understood the accuracy of the points doesn't go to 5 decimal places, I would send him the points.
James
I would not send the North East part of the file to .10' , I would send it to the .01' , but I would on the Elevations if it bothers you . For that matter whats the difference send him the points . Now hes out to prove you wrong . How is a ground shot going to screw you in the long run if you show it to the nearest .01' . I learned long ago Clients will leave, if you create grief for them in any direction . Pick your Battles
Yeah, that's my dilemma, djames. I don't think that I'm hanging myself by giving him the points.
But then later, should I be surprised if I see his drawing, with spot shots to 0.01', and 1' contours, and a note saying that all existing topo and contours are by me?
> ....I also wonder if I’m just being too stubborn...
The client's engineer is not smart in this area, and you are stubborn. What a great combination for the client. If you want to work with this group again give them a file to the hundreth. If you want to tilt at windmills, stick to your guns. Good luck.
If you really feel that to the tenth is good enough, next time, truncate your coordinates before you import them to CAD.
Make them sign and return an Electronic Digital Data Release form holding you harmless for any digital data, and then send them whatever they want.....
Heres what I do , Provide him a stamped drawing of what you did . Explain you are giving him the points as a aid for the project . After that he on his own . Document what you give him . Your stamped drawing should end up in the project plans . Lets face it we are in a digital world with the engineers . If you you dont give them everything it makes it hard on them . Make it easy, yes hes probably going to generate 1 foot contours buts thats on him. Give him a Landxml file of the Tin that way he dont need your points and its and exact copy of your tin file and there is no re-tinning by the engineer .
I always truncate the elevations to .1' before creating the DTM and contours. This avoids any (most) confusion, and the points then match the map.
> I always truncate the elevations to .1' before creating the DTM and contours.
Does that include points on well defined hard surfaces such as curbs, gutters, catch basins MH rims, etc? It is certainly possible to determine elevations on such things to a much better precision than a tenth, and reasonable for the engineer to expect you to do so.
Just an idea, but your concerns might be addressed with an accuracy statement that is attached to a hard copy deliverable. I.e. contours being accurate to within 1/2 the contour interval. This will prevent someone from mis-using your high precision files. You could even include something about the accuracy of the digital deliverables.
The individual points used to generate the deliverable could be very accurate, however the density of the measurements was reduced to reflect the desired contour interval.
If you took additional shots above what was necessary to produce a TIN accurate to within 1', then you could temporarily pull these shots out of the TIN and use them as check shots to prove your accuracy (95% of the check shots were accurate to within 1' of the elevation indicated by the TIN/Contours).
The ground is vacant woods terrain with no hard surfaces, how is anybody going to be able to reproduce your data within .05' in a way that will prove you wrong? Unless you had a systematic error, you should be fine.
EDIT
I suppose the 1/2 contour method is now considered old school since our products are being used almost exclusively digitally.
Jaro hit it on the head. Amending the points after creating the tin and connecting feature lines will wreak havoc on most digital processes. You have essentially devalued the digital product.
Leaving points where you measured them only implies precision if you allow it to. Every State has its own Rules governing digital products. Cross your t's and dot your i's to conform to those rules and above all make sure the client knows what they are getting. I don't stay awake wondering if someone has mutilated my digital products any more than my paper. I have a record of what I sent and if they amend it under my name the Board will deal with it.
For dirt only obviously.
I agree, I'll do that in the future. But this is the first time that I've had this put to me.
And I still contend that the points not being gnat's ass on the linework/figures doesn't make them unusable for the engineer.
I learned long ago that the deliverables include the coordinate file, whatever CAD file I used in whatever format I use - let them convert, and a sealed pdf of what you are certifying to.
If the guy wants to generate new contours, there is nothing you can do about it. Not much different than them placing building setbacks to the nearest 1/16 inch. Nor are you liable beyond your scope and what you certified to and all state boards do have standards. I would never put a "1/2 the contour interval" note on anything. What if a truck gets stuck, makes a bunch of ruts and the tow truck gets stuck with bigger ruts, now 2 ft deep ruts and knock some trees over ....yadda yadda yadda. That is why we date our surveys, what happens after is not your problem. Nor are "do overs", without a fee.
I'm not engineer beating, but a few have more common sense than the rest of them. My guess is they have a CAD guy with less than the engineer. Meanwhile the poor client is sitting there with a deer in the headlight "...huh, wtf, I just want my permits...". Me, I'd likely just provide the coordinate file to the 0.05' and not sign it.
I don't see what the problem is. Give them the points to the nearest hundreth and let them do their thing. Surely you stated on the plat that the contours are at 2' intervals per the client. I'm also assuming that you gathered the points close enough to have generated 1' contours, but just let the software stop at 2, right?
Send them the file and move on.
>I would never put a "1/2 the contour interval" note on anything
Title 09 DEPARTMENT OF LABOR, LICENSING, AND REGULATION
Subtitle 13 BOARD FOR PROFESSIONAL LAND SURVEYORS
Chapter 06 Minimum Standards of Practice
Authority: Business Occupations and Professions Article, §15-208(b)(4), Annotated Code of Maryland
(3) Vertical tolerances for topographic mapping shall meet the accuracy standards of this subsection. Vertical accuracy, as applied to contour maps on all publication scales, shall be such that not more than 10 percent of the elevations tested shall be in error more than 1/2 the contour interval. In checking elevations taken from the map, the apparent vertical error may be decreased by assuming a horizontal displacement within the permissible horizontal error for a map of that scale.
The language is straight from the national map accuracy standards.
With all due respect James, no mention was made of any national standards or ALTA issues. Every state is pretty clear in standards, and some of them cannot be "un-scoped" and disclaimers will not work. Most of them regard boundary issues, and keep utilities, topo, unrecorded documents out.
The issue here IMHO is that the project was scoped for one thing (2 ft contours, and 0.1 vert) and the engineer decides he wants more. Ok fine, now it's a business decision between the client and whoever he hired.
So what happens in Maryland can stay there. Shooting woods and dirt trails to 0.01 is a waste of money. Here in AZ, it is a scope issue. From my recollection of chain of command most states trump national - once outside the GLO or even ALTA. Many states still allow "mortgage surveys", and those certainly don't meet your mapping schedule. Don't try those here, but no problem in MI.
Just pointing out that whether you would specifically certify to the 90% within half a countour interval standard or not; it is, for all intensive purposes, the national standard of care for field run and controled aerial topographic surveys and, should the crap hit the legal fan, it's the standard that a professional will be held to in court. There is a reason it's been a standard question on the NCEES PS exam for decades.
