View Full Version : AutoCAD Civil 3D Subtracting Surfaces
26th Sep 2008, 08:38 pm
I am currently doing a drawing for cut and fill calculations in AutoCAD Civil 3d. I only have a brief understanding of the program, but I know how to use other AutoCAD programs. I've created a series of points for my existing ground, finished ground and for swales surrounding the area. I have also already built the surfaces for EG, FG, and Swales from a 2D contoured site plan. My problem is that I need the swales to be apart of the Finished ground surface.
When I add the swale points to the same point group of the finished ground, the surface builds around the swales, but the tin lines don't follow the swale edges (the go to the nearest point, which is usually an FG point).
When I create a surface of only the swale points, the tin spreads around the whole terrain (outside of the swales), and I have to delete the segments that I don't want (I can't get an inside border to work).
Is there any way that I can subtract my Swale Surface from my existing ground? If I need to create more points on my Swale, and then add them to my finished grade, how do I do it? my swale is a v-shape formed from 2 3D polylines. I want the points to be of actual elevation, and a certain distance apart along each polyline.
26th Sep 2008, 09:19 pm
Does your project only consist of this swale? If so I would recommend creating a feature line as the centerline of swale and use the grading tools to grade up from it to the existing ground surface. This way you know your tob of swale intersects the existing ground properly and you can get more accurate cut/fill numbers. You can tell it to create a surface from your grading group that you create if you wish.
As far as triangle lines outside the extents of your swale you just edit them out by going to "edits" under your surface data > right-click > delete lines and then select the lines to remove > enter.
Another way to minimize these is to go into your surface properties > definition tab > expand the build collection > use maximum triangle length > Yes and set the Maximum triangle length to a number about the length of the longest tin line within your swale or just a hair longer.
26th Sep 2008, 09:29 pm
The swale is not the only part of the project. There is a series of points I created from 2-D contours (I elevated them into 3D) for the Existing Ground surface. I created the Finished Ground Surface so that I can have a level plane to then put a building on (from CAD Architectural). The swale around the edge of the property is there for drainage.
8th Oct 2008, 02:38 am
Sounds like you need breaklines.
The surface modelling is created from points only you must add breaklines to cut the mesh into more triangles representing the true shape.
21st Oct 2008, 11:40 am
This seems to be an area that I also cannot get my head around. We are currently involved in some serious road projects and are using C3D 2009. We have managed to work our way through most of the issues with much pain. What we are stuck with now is how to clip the original surface so that the modeled corridors show both cut and fill when in 3D. We need this for the visualisation aspect of the software.
21st Oct 2008, 11:38 pm
You're venturing into an area of which I have no experience, but I believe you can do this by creating a TIN Volume Surface using your existing as the base surface and the proposed as the comparison surface. Then in the surface style I'm guessing there are display options for your cut and fill.
22nd Oct 2008, 12:55 am
After making a volume surface, rt-clk on it in Prospector.
Analysis type = Elevations
Change Ranges number to 2
Click on blue arrow
ID 1 > Maximum Elevation=0
ID 2 > Minimum Elevation =0
you can change the colors by dbl-clicking on them in the Scheme column
Surface style > Elevation Banding (2D)
or for C/F contours
Analysis type = Contours
Change Ranges number to 2
Click on blue arrow
Ranges as above
Surface style > Contours 1' and 5' (or to your choosing)
22nd Oct 2008, 12:57 am
But you can't make your own scheme and save it to your template right seifert.:lol:
22nd Oct 2008, 01:10 am
I gave up on Schemes the first time I tried to get a handle on them; my scheme is that I just change the colors as needed.
22nd Oct 2008, 09:52 am
I have tried this but does not give me what I want. When I do grading with cut to fill, it automatically creates a feature line at the limits of the cut and fill. I then use to the boundary tool to hide the data within this new boundary. This works ok as I then get to see in 3d the final effect. As for road corridors this same procedure does not work. So what happens now when I put the model into 3d, I cannot see much of my road as it falls below the existing surface.
There has to be a simple explanation
22nd Oct 2008, 01:10 pm
Have you created a surface from the corridor?
27th Oct 2008, 08:49 am
yes, I have created surfaces for all the coridors and gradings. It is only now how to clip the original surface to allow the new corridor surface to show through.
27th Oct 2008, 01:32 pm
I would copy the original surface and set the original to a style that does not display. Then paste the corridor/gradings surface into this new copy of the original surface. Then you will be able to see it.
28th Oct 2008, 08:22 am
Thanks will try this but it seems like a round about way of doing something I though ought to have been a part of the software.
28th Oct 2008, 02:36 pm
Another way to do it would be to add a hide boundary to your existing surface so it won't display within the proposed model.
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