The Hybrid Approach to 3D Modelling


Civil 3D is a great software package for creating Civil objects, obviously, but sometimes we tend to forget about the fact that it is built on top of AutoCad. What does this mean for us as users? Quite simply this means that we have access to a boatload of commands in addition to the Civil commands in Civil 3D. This fact can come in handy. One example is linework. All of the basic AutoCad creation and editing commands can be most useful in Civil 3D as most of you are fully aware of. What about the area of 3D modeling? I know, it’s called Civil “3D” because we can make 3D Civil objects, but have you ever considered what AutoCad 3D functionality can do for you? I recently worked on a project where this functionality came in quite handy and gave me the results I needed with less effort and file size then if I used just Civil 3D objects. I ended up combining Civil 3D objects and AutoCad objects to achieve my goal. This combination is what I like to call the Hybrid Modelling Approach. Let’s take a look at some of these examples.

In one project, I needed a big concrete structure that was to be constructed in a canal. There were no Civil objects close to this in the part catalog and by no means was I going to attempt to construct it using Part Builder. Not only am I not that proficient with Part Builder, but this is a complex radial gate structure that I am talking about so I’m sure it would have taken quite a bit of time to create. Since I had already created some Civil objects in the project such as TIN surfaces and pipe networks, I figured that I could use AutoCad 3D objects to get the job done. I was right! What I did was I used the 2D linework that I had of the structure and referring to the cross sections for the dimensions, I extruded the linework to the proper height to create an AutoCad solid. Once that was created, I used the UCS Gizmo to move the object to the proper elevation in the model. The finished object can be seen in Figure 1 below. As you can see, this object has multiple pieces such as stairs, guardrails, walls, etc.

Figure 1

Figure 1

In another project I worked on, I needed to create a pavement structure that not only had the different pavement levels, but I also had to have it split up into sections to eventually tie it to a construction schedule to show the construction phasing sequence. Wow! I though about using a corridor but decided that showing the individual pavement levels might get tricky as well as chopping it up for the construction sequencing. I then thought about TIN models, but quickly decided that it would take a ton of TINs and I know that can cause issues within the dwg file. I finally decided on using AutoCad solids to get it done. Once again, I utilized 2D linework and then extruded the objects to the heights that I needed them. When the bottom level was done, I simply copied it to the top of itself to create the next pavement level, modified it’s height, then changed it to the proper layer so that it would assume the proper color from the layer. I repeated this for the top pavement level. To get the different pavement levels split up for the construction phasing, I used the “slice” command and simply picked where I wanted the objects to be sliced. Figure 2 below shows the 3 pavement levels and shows a slice on the top level.

Figure 2

Figure 2

Once again, AutoCad 3D modelling combined with Civil 3D objects got me what I was looking for to complete the project and provide a kick-butt 3D presentation.

The last example I will discuss is when I had to get construction sleeving for pipe networks modeled for a project. Now, visibly, I possibly could have gotten away with using an oversized pipe and pointed it out as sleeving, but, the actual pipe needed to stick out just a bit from the ends. So, quite simply, what I did was draw a circle at one end of the pipe, give it a thickness, and then exrude it. The results are in Figure 3 below.

Figure 3

Figure 3

Using the combination of Civil 3D objects along with AutoCad 3D objects gave me the results I needed for these projects and made me a believer in the Hybrid Approach to 3D modelling.

Civil Infrastructure software is my main professional interest. Civil 3D, Infraworks, and Recap are what I work with mostly. I have been with CADsoft Consulting for over 10 years now. I got my start using Softdesk and AutoCAD R12 in DOS. My wife and I have four children and I am a die hard Red Sox fan.

One thought on “The Hybrid Approach to 3D Modelling

  1. I read this with interest, I often use hybrids of TINs and 3D primatives.

    My example, used often would be a TIN of general finished site levels, any other associated TINs for formation grade etc.

    Then I’ll use primatives for any ringbeams / retaining structures, these then feed into any detail sheets etc.

    I also cut profiles through the TINs with C3D and and use AutoCADs sectioning tools to section any primatives along the same line and overlay the two.

    Superb tools

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