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TIN Question
Posted by transitman on June 14, 2022 at 6:18 pmI have been asked to provide a TIN (triangulated irregular network) for a project that I worked on some years ago. We only had a couple of contours, so we created these ??by hand?? with no TIN. The request for a TIN comes from an engineer who will be conducting some design on the project, and he is willing to pay for my producing a TIN.
My questions has to do with liability and risk. I believe that a TIN is similar to internal notes and calculations which I don??t think any surveyor would send out. A TIN is a part of a process leading up to contours and is, of course, subject in any normal functioning survey office to review and checks. For example, a surveyor would typically look at vertical surfaces like curbs and walls and make sure that the contours respected them. I am afraid that the TIN may be used incorrectly with bad results and that the engineer would say some version of ??Well, I just used the surveyor??s data??? Should I provide a TIN to the engineer?
By the way, this engineer is known for having his engineering design done almost exclusively by computer drafters.
Norman_Oklahoma replied 2 years, 2 months ago 13 Members · 17 Replies -
17 Replies
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If he’s willing topay for it, I’dmake it and send it to himwith the disclaimer that the elevations represent what they were at the time of the survey. He doesn’t need the TIN to screw up a design and if he does screw it up, that’s on him as lone as you retain the original TIN as part of your records.
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What were your quality control measures when you created the contours by hand in years past? Did you spot check your contours after they were drawn? Does the ground still look the same today as it did in yester-year? If the answer is yes to the last 2 questions, a surface can easily be created by tracing the contours with 3D polylines in AutoCAD C3D (slightly more complicated than a 2 step method). If any significant time has passed since you were last on site, I would personally elect to re-survey the area using modern equipment & methodology.
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Posted by: @transitman
We only had a couple of contours, so we created these ??by hand?? with no TIN.
I see two options here: use the original data (that you used to create the contours) to generate a TIN, or generate a TIN from those “hand-entered” contours. Either way it’s derived from the raw data.
I’d be sure to include a disclaimer about the intent of the original project survey, emphasizing that the data were gathered for that purpose alone, the TIN was derived from that data, it is not intended to be used for anything other than the original project. Whatever this engineer does with it, and how they rely upon it, after that is their business. Make sure they understand that they are not paying for a survey – the contract should reflect that – but for data that may or may not be what they are looking for.
If they don’t like those terms, you’ve lost nothing and aren’t sticking your neck out.
Posted by: @transitmanBy the way, this engineer is known for having his engineering design done almost exclusively by computer drafters
That’s not surprising, it’s pretty much SOP for engineering. Designers do the grading, utility runs, details etc., then the engineer reviews and modifies if needed. Same with surveyors and field/office staff.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
Posted by: @chris-bouffard
If he’s willing topay for it, I’dmake it and send it to himwith the disclaimer that the elevations represent what they were at the time of the survey. He doesn’t need the TIN to screw up a design and if he does screw it up, that’s on him as lone as you retain the original TIN as part of your records.
^^^ This, exactly. I see no reason not to supply an engineer with a TIN that you have full confidence in. Your liability would be no different than if you supplied poorly drawn contours. Frankly, with the design software available now, I’m surprised I don’t get more requests for TIN data when I send topo plans to designers outside my office. I’m doubly surprised the engineers within my office don’t make use of Carlson’s design routines that work with proposed TINs.
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Sharing data in electronic/digital format is just part of the world we live in these days. Prepare your files accordingly. Archive an exact copy of what you sent.
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Posted by: @peter-lothian
Frankly, with the design software available now, I’m surprised I don’t get more requests for TIN data when I send topo plans to designers outside my office. I’m doubly surprised the engineers within my office don’t make use of Carlson’s design routines that work with proposed TINs.
^^^ This, exactly.
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TINs are standard deliverables here. If you don??t include it then you can expect a phone call when it gets to the designers.
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Posted by: @norman-oklahomaPosted by: @peter-lothian
Frankly, with the design software available now, I’m surprised I don’t get more requests for TIN data when I send topo plans to designers outside my office. I’m doubly surprised the engineers within my office don’t make use of Carlson’s design routines that work with proposed TINs.
^^^ This, exactly.
Engineers who don’t use EG TINs are usually the same engineers who pencil-whip everything and hand you digital drawing files without FG surfaces or profiles or grading lines, composed of flattened 2D polylines along with paper/PDF plans whose grades don’t match spot elevations.
I used to be a lot more patient about stuff like that. Nowadays my RFI trigger finger is very very sensitive.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
You cannot back your TIN in from contours and expect accurate results on most all sites unless the site is all composed of straight grades. This would only work if the surface is completely uniform, otherwise the TIN would miss any variation in elevation between contours. For example, when straight line Tinning between the 1 and 2 foot contour line, the actual elevation could be anywhere between 1 and 2 feet and you wouldn’t know it. With an accurate TIN created from the source data, you would.
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Most site definers just ask that I use polylines instead of “conture” linework. With half-foot intervals being most common, and live spot elevations at the confluences, intermediate highs and intermediate lows; they ‘say’ their system works better with a created TIN than an imported TIN.
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We have many clients that we send out TIN, DGN, DWG, ASCII files all the time and it’s standard procedure to let them know they are in preliminary phase. I agree that a disclaimer about the TIN representing the ground and the intention of the TIN for that particular project it was used to has to be included.
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Do you have the field data still? Why can’t you create a tin now with that data?
Not for free, obviously.
Bottom line is if you want to do this, there are a few ways, but if you don’t, it’s easy enough to say that it was done in the past when you contoured by hand, but if they want an updated topo with tin, you’d gladly send them a proposal for the work.
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Posted by: @transitman
Should I provide a TIN to the engineer?
I think the first thing I would look at is the data I collected back in the day. Is it sufficient to build a quality tin from in the first place?
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Posted by: @transitman
a project that I worked on some years ago.
Posted by: @bstrandI think the first thing I would look at is the data I collected back in the day. Is it sufficient to build a quality tin from
The first thing is to get some idea of whether the site has changed significantly in the intervening years.
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With the price of things these days … I think I’ll look at the data first to see if I have something I can sell before I waste gas driving to the site to inspect for changes. This is like one of those exam questions that asks you what the first thing you should do is.
Also – remember that the surface data is worthless if there are no existent monuments in the data set as well.
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@norman-oklahoma
Good point if the site is a significant distance away, though for the wrong reason. Even at today’s gas prices, the time cost of a site visit is probably more than the gas.
But at least use Google Earth and/or GIS aerials to see if it looks altered.
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The point of it is that you do both things before you ship any deliverable. Which you do first is immaterial.
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