Contouring Hard Surfaces

Welcome,

the major part of our surveys are for road design and we contour mostly everything ...
it needs some extra shots on curbs and gutters but since most are prefab here we shoot these points with templates/parallel lines.

Chr.

We pretty much contour everything. I do a lot of design surveys for engineering companies, and they want information on anything and everything within the design area.

It definitely takes a lot more shots. In areas that do not generate many contours, I generally show spot shot elevations.

I don't really think too much about it. I have been doing it that way for the 18 years I have been in the surveying profession.

If you are going to do a topo, do a topo. You contour everything.
How's an engineer going to do his storm drain stuff if he can't see the crown flow on the roadways?? If you don't have the curb line deliniated in your tin, you will not have acomplete surface. You cannot design an overall plan with an incomplete surface. AND, what you "eyeball" as totally flat, usually isn't. All that hard surface has crowns and slopes for storm water run off and you are not showing it.
In my 44 years of mapping , this is the first time that I have run across the concept that we do not need to contour hard surfaces. My clients would pitch a hissy fit if I did that!!

I did not say I don't contour hard surfaces. I was merely suggesting that having just one contour over a large area can look a bit pointless and is better with just the spot elevations.

I dont think you can just say contour everything. What about steps?

contours come in and go out of steps

If you aren't showing any contours then your contour interval is too large for the project. Nothing stops contour intervals from being shown at 1/2' or 1/4' intervals.

> If you aren't showing any contours then your contour interval is too large for the project. Nothing stops contour intervals from being shown at 1/2' or 1/4' intervals.

Moe,

While nothing stops the software from creating contours at a 1/2' or 1/4' interval they will not be correct unless you take an adequate number of shots to depict the surface at that resolution. For most road design surveys a 1 foot interval should be fine.

While only a few contours may show up, it is the DTM/TIN that gives the engineer the whole picture.

> What do most people do here, do you contour everything?

Most of my work is in a pretty flat area, where slopes less than 1% are common. I generally show a 1' contour interval, but I don't bother with curb height unless it's specifically requested, which is rare. (So rare I can't remember the last time I did it.) On a typical street section I'll show centerline, gutter flowline and back of walk grades, and I contour right through the curb. The engineers use the contours to get a general sense of site drainage, but rely mostly on the elevations to guide their designs.

If our project is for design purposes we will create a 3 dimensional surface that can be contoured. Most Clients concerns are for whatever their engineer or architect is going to use, so we ask up front what is needed for a deliverable. Many times it is a cad file with a complete surface and boundary rathern than a printed hard copy. If your deliverable is simply a map then I could see how one could save time by only contouring sloped areas to depict on the map. We just don't have many projects where the map is all that is required.

Welcome, and thanks for posting.

While nothing stops the software from creating contours at a 1/2' or 1/4' interval they will not be correct unless you take an adequate number of shots to depict the surface at that resolution. For most road design surveys a 1 foot interval should be fine

Many of the parking lot/site designs I've worked on work much better if the engineer uses a smaller contour interval.

Twice I've had an engineer design new sidewalk/streets to the low grade of curb cuts. This of course ended up screwing up the design when just running 1/2' or 1/4' contour intervals in the parking lot areas would have highlighted the curb cuts. I recommend to all my engineering clients that for tight sites just run the 1/2 or 1/4' contours and it will pick-up many details that I locate. After all they have me locate everything and then skimp on the visual. Doesn't make sense to me.

Each job should use the correct contour interval. I've worked on mapping jobs that covered up to 1200 sq. miles at 20' contour intervals to small flat sites where there was only 2' of drop across the entire project and 1/4' intervals were the correct interval. I don't know why there is some built in distain for using them with surveyors and engineers.

> I don't know why there is some built in distain for using them with surveyors and engineers.

In my case it's not disdain, but rather a matter of giving the client what they ask for. A 1' contour interval is the norm where I work, although on most of the densely-built sites I topo the contours serve more to clutter up the map than to impart useful information.

This is a snippet from a typical site I did recently on a university campus:

It's bad enough with 1' contours; a smaller interval would just make it worse.

As Jered noted, the designers can use the TIN that's included if they want to generate more contours, but I'll stick with 1' unless I'm specifically asked otherwise.

I would normally use 250mm contours (approx 1') for most topo jobs, but where the hard surfaces are flat and an accurate form needs to be depicted to identify areas which might pond then I set a closer contour interval for those areas only (perhaps 50mm, about 2").

My software lets me do this automatically (sets a slope below which the closer contour interval applies), but you could do it by forming a second model of the road surfaces only and contouring that at the close interval.

> While nothing stops the software from creating contours at a 1/2' or 1/4' interval they will not be correct unless you take an adequate number of shots to depict the surface at that resolution. For most road design surveys a 1 foot interval should be fine.
Quite true. Still, it is very possible to model a road surface accurately enough to justify 0.1' contours. ODOTs (Oregon) confidence reporting system requires that DTMs be tested to prove that hard surface areas are accurate to 0.1' interval. It doesn't require heroic efforts to make a DTM pass that testing. The trick would be to show 0.1' interval contours on the hard surfaces and 1 foot interval contours elsewhere.

Most of the topo work I do for engineering firms has been F to F since about 1987. I send them a coded file and they draw it. The original system I was introduced to was the HASP system of coding. Now most firms are using micro-station.

Very few projects I do are drawn in-house for engineering design work and it took years to finally get them to see the benefit of tighter contours that highlight 6" curbs, cut-outs, handicap ramps and such, but now that they use them they aren't going back. The contour lines are on a layer and are turned on and off as needed. They are typically screened on the final drawing and don't clutter the drawing. If there is only one contour showing on the project what's the point?

I would normally use 250mm contours (approx 1') for most topo jobs, but where the hard surfaces are flat and an accurate form needs to be depicted to identify areas which might pond then I set a closer contour interval for those areas only (perhaps 50mm, about 2").

Exactly!!!

It's just here in the USA it's: we've always done it this way and we are always going too. 😉

Shoot everything to allow the software to interpolate the contours.
Let the contours tell the overall story...
Then SUPPLEMENT the contours with spot elevations to provide DETAILS.
An engineer can obtain data from the surface modeling structure.
But is engineering not much easier when data is visually sufficient to design from...

A review of the provisions for photogrammetric national map accuracy standards gives some guidance.

"I may or may not include contours on road surfaces, concrete etc."

Steps are not part of the topography unless they flow with the land. Then, yes, you contour the steps. If they are up to a dock, or other elevated feature, then you do not.
Perhaps you need to review the definition of "topography". ALL topograhy is contoured. Elevated, man -made features are generally not called "topography".
In the "flats" the contours are supplemented with spot shots.
You have to be able to tell the differance between "plannimetric" features and topographic" features. That will generally tell you where you need contours.

Take a look at older USFS topographic quad maps for examples of quality contouring. Contour display should vary as a function of slope. The key is to have index contours at, say 5 feet, and intermediate contours at, say 1 foot. Write the specifications such that when the index contour spacing is less less than X depending on map scale, intermediate contours shall not be shown. Index contours are one line weight heavier than intermediate contours. Adjust to suit, 1 foot index contours with 0.2 foot intermediates in flatter country, for example.

Pepper the really flat spots with spot elevations where necessary, and Bob's your uncle.

I agree, show spot elevations in flat areas. If the client wants more precise contours the field work changes and needs a new contract.

No disdain here, just business sense. For instance, one might get a contract to topo a basketball court. NCAA has guidelines for flatness. So you grid it out and take shots every inch or so and show half inch or so contours (don't remember the details). If the court doesn't pass, then the college must replace it.

But you gotta have the data to back up the presentation. Spot elevation is the only way to achieve that if the contracted for specificity is not showing areas of concern and the client does not want to spend more money.