shoreline grading

[Anonymous]

no excuses but i don't know how to do this correctly and efficiently:

if you are asked to grade a lake with proposed (really) curvy shoreline (let say elevation 39) to lots of proposed depressions in the lake, let say one of the depression is at elevation15)- imagine the bottom of the lake is like the moon with lots of deep craters - how would you do it?...oh, i also need to make all the contours really curvy, i tried to add breaklines on the surface BUT most of the time it does not work...any idea?

[Neilw_05]

It's not clear to me what your objective is. Are you wanting to calc the volume of the lake to elevation of 39? Are you simply wanting to establish the 39 elevation contour? Are you wanting to fill all depressesions lower than a certain elevation?

Could you please clarify?

[Anonymous]

basically i need to re-create the lake to its somewhat original appearance - good for fishes - shoreline elevation is already drawn on plan to make sure it is curvy (lots of coves) and an elevation is set, then i need to grade from that elevation to all the scatterd mini depressions in the lake...do i really need to grade it by section using different types of grading?...

[Anonymous]

After reading both your posts, I still have absolutely no idea what it is you are trying to accomplish.

What are you trying to do? Do you need to create a "Lake" surface at that specific contour and grade from that?

Explain in as much detail as you can, without getting so specific we lose you.

[jmayo-EE]

I have not seen what you are really doing or how big this shore line is but due to the highly irregular nature of a lake/pond, you may be better off simply using contours to define a surface for the bottom of the pond and add breaklines, points and/or contours to define the depressions.

[sboon]

As I read it the OP is trying to create a natural appearing lake bottom, with slopes and valleys, high and low points etc.  Think of how you would grade a golf course, but underwater.

For the OP - I would suggest that you look at the feature line editing tools available on the Modify tab of the Ribbon.  Stepped Offset is definitely going to be useful for you, as well as the Elevation by Reference tools.  For example - you could use Stepped offset to create a lake bottom from the waterline that you already have, then you could create some randomly shaped closed featurelines, force them to match the lake bottom elevation then use stepped offset again to create hills or depressions.

[Joe-Bouza]

Hello Amelia

make a feature line of the shoreline(this would be the really curvy edge of water) set the FL to the water elevation. Now, presumably we know here all the depressions are - add points for the low points.

Create a surface and add the data from above. Now you'll need to determine the height spots between the craters - add point for those.

Add to surface and you should be done.

You could also do this with all FL, basically making a spider web of the lake bottom.

You'll get there I promise.

Joe

[Neilw_05]

First off, can we assume you have contours on your proposed plan? If so you can use those to model the lake bed. Also, you can use those contours for display. I would not put a lot of effort into building a smooth model if all you need is earthwork QTY's. It can be a lot of work to create a smooth curvy surface that you can use for generating contours.

I believe 2012 now supports splines. If so you might try using plines to get smooth curvy gradings.

[Anonymous]

Does the lake bed need to conform to any grading criteria? If not, you may find some other software that can create the basic terrain for you more efficiently which you can then import back to C3D. For instance, I do a lot of work with topography and find that google sketchup is a great tool for playing around for this sort of stuff. The main benefit is that there are heaps of free (or dirt cheap) plugs that allow you to create and manipulate TIN surfaces (subdivide triangles, smooth, add bumpiness) to create a natural looking surface. Other plugs in allow "soft select" of areas and drag them down to make crater like depressions very easily. Once you're happy import the surface back into C3D to calc volumes, contours, add site plan, etc. 

If you provided more detail on scale and level of detail required it would be helpful.

Cheers

- Mick

[Anonymous]

Well, you are ALL VERY HELPFUL for giving me ideas plus making me feel better that i'm not wasting the project's time because i may have already tried one or two of what you have mentioned and yet i could still not get the "nice curve"...but i will definitely try all your suggestions to get to the closest design requirement as much as possible since the major reason they agreed to use civil 3d in this project is more accurate earthwork Thanks so much!

[sboon]

The problem sounds interesting.  If you can post a drawing with some info about what you're trying to achieve then some of us may be able to put together some solutions.

[Neilw_05]

Nice suggestion about Sketchup. I'd didn't know the models could be used for C3D surfaces.

[BrianHailey]

One thing to do is to draw contours (not necessarily every contour) with polylines and then spline the polylines (don't use splines, just splined polylines). You can then add those splined polyline contours to your surface. Because you are grading something that is so irregular and you want it to be smooth and undulating, this might be an additional tool to what others have already mentioned.

[Anonymous]

Neil,

I wouldn't go so far as to say that sketchup can use C3D surfaces, but it can import and export CAD formats (the pro version does this natively, and there are plugins for the free version to acheive the same thing). So a bit of mucking about import/exporting, but if you plan your workflow out it's pretty pain free and I find sketchup has been a great addition to the arsenal.

Cheers

- Mick

[Anonymous]

Ahhh... when I wrote "TIN surfaces" in my first post, I meant it in the generic sense, not specifically C3D.... sorry about that. - Mick

[Neilw_05]

I'm confused. You said you can use the imported sketchup surfaces to calc volumes, create contours, etc. and yet you say that they are'nt TIN surfaces. C3D needs TIN surfaces to perform those types of tasks does it not? How does this work? 

[Neilw_05]

This article discusses the new-to-2012 ability to use 3D splines in surfaces.

http://beingcivil.typepad.com/my_weblog/2011/05/autocad-civil-3d-2012-preview-3d-splines-to-create-c...

I haven't run through the process to use them as contours so I don't know what issues you might encounter.

[Anonymous]

Hi Neil, if you want confusion I'm your guy !. I'm a complete newcomer to C3D and I've probably been a bit loose in my terminology which hasn't helped at all. The only real point I wanted to make is that sketchup has some pretty good tools available for adding moon like craters to a lake surface and that this geometry can be imported into C3D and utlised in a C3D surface.

See the attached for an example. It took about 5 minutes to create the top shape in sketchup by freehand, but with a bit of planning and more time, it's entirely possible to put together completely to scale geometry to the right elevations using either contours or spot heights, and then add "features" such as moon craters freehand. The workflow I used to get this as a C3D surface was to:

- use C3D to open the DWG which was exported from sketchup

- explode the geometry

- create a new TIN surface in C3D

- add drawing objects (lines) to the new surface definition

The only issue with a shape like this one is that the surface triangulation doesn't recognise the original geometry boundaries. I believe there is a way to fix this but I haven't explored this yet. It would be great if someone could explain how that can be acheived (I've just manually deleted the unwanted geometry previously). [edit: actually, now that I look, I guess it is with surface boundaries?]

Cheers,

- Mick

[Anonymous]

OK don't worry, I figured out the surface boundary thing... I'm not sure how you guys find outer edges of geometry, but I found a command called "_aeclineworkshrinkwrap" which gave me a polyline for the imported geometry, that I could then use as a boundary to add to the surface to clean it up like the attached. Cheers - Mick

[Neilw_05]

I understand what you are doing now Mick. It is a good technique for modeling curvy terrains.

I was going to suggest the shrinkwrap command. Sometimes it doesn't work well so I'm glad to know it does the job in this scenario.