is there a way to do a topo to best fit a specific contour interval? I guess we’re doing a design survey because it’s for a new sidewalk. Would an engineer or a surveyor determine the contour interval in my case?
is there a way to do a topo to best fit a specific contour interval?
The shape of the ground is what it is. Unless the ground is crazy steep a 1 foot contour interval works for well for almost everything in my experience.
We code breaklines and solitaire 3d-points. Some are used, others not, to build a DTM. With this DTM we can then build all contour-lines we may need. During QC that can be each 2”, for delivery it depends mostly on the height variations of the terrain, but 1 foot will do fine in a lot of situations over here.
Would an engineer or a surveyor determine the contour interval in my case?
would depend on who is paying for it
also, you do not mention if need be ADA compliant.
Don't think in terms of contour intervals. Think in terms of the accuracy of your digital terrain model (DTM). In order to be able to effectively design a sidewalk your engineer will need a model that is accurate to perhaps 0.05'. If you go with the old standard of accuracy to 1/2 the contour interval you would need 0.1' contours. Such a drawing would be nothing but solid contours and engineers don't extract elevations by interpreting between drawn contours anyway. They query the model. So mostly we show 1 foot contours but that is just for show.
That old 1/2 the contour interval standard was written in 1941 and, I think, was intended to apply to USGS quad maps, not engineering surveys.
Regardless of what is being built no one should certify a surface accuracy to 0.05' that includes soil as part of the surface.
you do not mention if need be ADA compliant
No, because there aren't going to be any crosswalks. Good point.
Regardless of what is being built no one should certify a surface accuracy to 0.05' that includes soil as part of the surface.
Quite true. ±0.05' for finished hard surfaces, probably about ±0.2' for graded ground, and ±0.5' for natural ground.
Does the rod have a foot or a tip? As one seeks perfection, such things matter. If the grass grows in clumps or not can make a difference on perfect measurements? Small erosive area matter in the search for perfection.
OR
Consider that all the sod will be removed to a depth larger than the intended concrete thickness, so the underlying pad is compacted fill feathered to a certain elevation along the sidewalk plan. Thus that perfect model of the surface will be gone once construction starts.
Does the rod have a foot or a tip? As one seeks perfection, such things matter. If the grass grows in clumps or not can make a difference on perfect measurements? Small erosive area matter in the search for perfection.
I was on a project once where we needed to topo a large, occasionally used gravel pit. Some kids got in there with ATVs and made some tracks, etc. I went through and mapped maybe half of it and then a party chief from another office came in to help so I shared my points with him. He started comparing what I mapped to what was out there and started whining about shallow moguls here or there that I skipped over. I was like look man, you could spend a week in here or 2 months. The stuff I wasn't picking up wouldn't have amounted to a hill of beans in the grand scheme of the project, but this guy was acting like I was insulting the survey gods. 🙄
Anyway, one of the more ridiculous mapping issues I've run into over the years.
Does the rod have a foot or a tip? As one seeks perfection, such things matter. If the grass grows in clumps or not can make a difference on perfect measurements? Small erosive area matter in the search for perfection.
I was on a project once where we needed to topo a large, occasionally used gravel pit. Some kids got in there with ATVs and made some tracks, etc. I went through and mapped maybe half of it and then a party chief from another office came in to help so I shared my points with him. He started comparing what I mapped to what was out there and started whining about shallow moguls here or there that I skipped over. I was like look man, you could spend a week in here or 2 months. The stuff I wasn't picking up wouldn't have amounted to a hill of beans in the grand scheme of the project, but this guy was acting like I was insulting the survey gods. 🙄
Anyway, one of the more ridiculous mapping issues I've run into over the years.
Always funny how some engineers need such tight topo to mass grade a site.
Always funny how some engineers need such tight topo to mass grade a site.
My comment about 0.05' accuracy clearly does not apply to every surface type of a site. The OP claims he only needs to survey graded, sodded ground. But surely there will be match points somewhere in this that need to be known more accurately. My main point is that the surface accuracy be thought of in terms of the point tested model and not in terms of contour interval.
@gary_g This wasn't even from an engineer though, this was just an anal party chief. 😆
Always funny how some engineers need such tight topo to mass grade a site.
Every EIT needs an experienced surveyor who's not afraid to look him/her in the face, early in their career, and say "are you f***ing stupid or what?"
I had some wild requests from some. Two architects come to mind. One wanted me to pick up some desk drawer sized piles of dirt on a 10 acre site I had ignored. I refused to return to waste everyone's time. The worst was a new architect that said I missed trees on a community senior center that was going to be redone for a new building. It was a small area packed with suckers and she wanted each "trunk" (hundreds of them) individually located instead of me just showing the area as a group on my drawing. These "trees" weren't even head high, just weeds really. I refused that request also.
These "trees" weren't even head high, just weeds really. I refused that request also.
You just reminded me of the time I was staking through an easement to flag for clearing that was full of these Quaking Aspen suckers, maybe head high and this Karen comes over and asks what we're doing and I tell her they're getting ready to clear this easement and she completely freaks out, screaming at me that the Aspens suckers are screaming in fear and she can hear them from her house. She then calls the cops and threatens to chain herself to a 1/2" thick Aspen to stop the clearing from happening. My phone is blowing up asking me what's going on and everyone I try explaining this to won't stop laughing.
Just because I'm paranoid, doesn't mean they aren't out to get me.
Always funny how some engineers need such tight topo to mass grade a site.
Every EIT needs an experienced surveyor who's not afraid to look him/her in the face, early in their career, and say "are you f***ing stupid or what?"
Oh the many, many times I wish I really could have done that, and not restricted to EIT's, but PE's also, particularly when I was at AKDOT&PF
US National Map Accuracy standards still use a reference to the "1/2 contour interval" in the context of - whatever your shown contour interval is, 90% of random points selected must fall within the 1/2 contour interval range at that point vs a "real elevation" on the ground at that point.
So I think if you're showing contours, any engineer would base a design from your drawing on that rule of thumb. When shooting existing topo for design, I think the best approach is to understand how a modeled TIN and breaklines define your existing surfaces, so if your proposed sidewalk (are you shooting for design or an shooting existing sidewalk?) is changinging grade quickly, going up over hills or sagging in depressions you'll want to space your shots more closely at those more dramatic changes in grade