Hardscape & Site Topography for First Timers

March 17th, 2014

Are you a beginner in Autodesk® Revit®? Are you a beginner at using the topo modeling tools in Revit? Are you a beginner at using methods to create hardscape elements that follow site topography exactly? If you answered yes to any of these questions, then you are a beginner in regards to the material covered in this article and you need () to read on! If you answered no, read on as well—this article may just illustrate that there is more out there to know.

Site Topography: A Love/Hate Relationship

I first thought that the site topography modeling tools in Revit were “clunky” compared to other Revit modeling tools, but over time I learned to respect them. It’s not that they are clunky; they just use a different set of rules so it is understandable that some Revit users do not like them.

I have also heard, and once believed, that it was frustrating working with site topo elements because they do not like to “interact” with other elements. I hope this article will help you appreciate the site topography tools and give you a better understanding and better tools and methods to work with site topography.

To do this correctly, the methods presented include modeling and importing elements that are used only for the creation of other elements. These are called “sacrificial elements” or “guide entities” because their sole purpose is to be used as temporary aids in the modeling and creation of other final elements.

Parking Lot That Will Dynamically Adjust

In this example we will explore how to create a parking lot so that when it is moved it will dynamically adjust to the shape of the topography or it will adjust if the topography is adjusted…automatically.

1. Create any topo and locate the shape and size of the parking lot.
2. Go to the site plan go to the Site Tab> Split Region. Draw a rectangular boundary as shown in Figure 1 to represent the extents of the parking lot. The final boundary is shown in Figure 1.

Figure 1: Parking lot location

3. Go back to the default 3D view and select the “split surface” element, which is now a separate topography element.
4. Isolate and export that new split topography element as a dwg. Make sure not to export all the temporarily hidden elements. Save the file exported dwg file.
5. Undo the split surface command (or merge the surfaces) so that there is no “hole” in the site topography element. Insert the newly exported dwg as origin to origin, level orient to view, in the project environment.  It is also a good idea to change the color to black and white so the mesh lines are easier to see as shown in Figure 2.
6. The dwg insert should line up perfectly with the site topography element. You know you have it in the right location when there are many mesh lines that show up in the same location as the topo as in Figure 2.

Figure 2: Parking lot imported dwg

7. Build entourage families—build the guides and place the families.

Yes, I said entourage families. You will use entourage families to host the path geometry. Why do this?  Entourage families and a few others (I prefer entourage families) are the ONLY families that host to site topography (at this time). Meaning when you place an entourage family on a site topo it will follow the site topo even if the family is moved. Therefore, if you host the entire lot to entourage families and the entourage families are hosted to the topo, then when the entourage families move the lot moves as well—all the while following the topo surface. Also, if the site topo were to change, then the lot that is hosted on the entourage families will also change!

To build an entourage family that is usable, simply open the entourage family titled “Van” then delete everything and go to the left elevation view. Add a vertical model line that starts at the origin of the family and extends straight up. Place a parameter on the height and call the parameter “HT.”

Although making a parameter out of the height is not required, I prefer to do it so in the future I am able to adjust the height of my path in the “z” direction as shown in Figure 3. Finally, change the settings of the family to be always “vertical.” This will make sure that the family “line” always points up. Save the file and load it into the project.

Figure 3: Parking lot dwg

The only reason that you imported the dwg into the project environment was so the entourage families have a “guide” or something to “click” or “snap” to. Otherwise these families will not “snap” to topography.

Add one entourage family and array the rest as shown in Figure 4. In this example there were 44 arrayed families in the long direction and 11 in the short direction of the parking lot as shown. The amount of families you place is entirely up to you; however, the more families, the more adaptable the parking lot will be when it is placed on undulating topography.

Figure 4: Parking lot entourage

8. Build the rig

Host the nodes of the splines that will make up the parking lot surface to the entourage line families that you just placed in the previous step.

Simply host a point anywhere along each line—it doesn’t matter where, as long as they get hosted (as shown in Figure 5), then make a spline thru points. Select all the splines (as reference lines) and select “make form.” Note: It is easier if you isolate the entourage families when doing this step.

Figure 5: Parking entourage with hosted nodes

9. When that is completed, select all the nodes and make a parameter to set the relative location of the nodes to the bottom of the line or equal to “0”.
10. Build the parking lot by simply activating the Roof by Face command and select the mass surface. The new “road” should look like Figure 6.

Figure 6: Parking lot with mass rig

11. The fun part is to now move the lot out of its current location from the flat part below the helical path and watch it dynamically adjust to the topo surface. To do this, go to a 3D top view and simply select all the entourage families that are being used to “host” the splines. I found it helpful to place all the families in a group. Move the entourage families and watch what happens. The results are shown in Figure 7. This parking lot and site were used to illustrate an extreme example of a topo shape and in common practice you will not likely see a parking lot need to take this final shape.

Figure 7: Parking lot adjusting to topo

How to Model Helical Site Topo

In this section you will be creating a helical mountain.To creates a mountain out of the topo tools you first have to create a “guide” family.

1. Create a new project with a simply flat topo element.
2. Start an in-place mass.
3. Place a circle at the base of the project and use the grids of the project as a guide.
4. Break the circle into two semi-circles as shown in Figure 8.

Figure 8: Create two semi-circles

5. Select each semi-circle and click “create form.”
6. Simply grab the top end of the extruded half cylinder node and drag to desired height. Behold a helix in Revit as shown in Figure 9.
7. Instead of dividing the edges, simply draw a curve along each edge using the Spline Thru Points command and the “follow surface” option turned on. Isolate the edges one at a time and export them to a dwg file as shown in Figure 9.

Figure 9: A helix in Revit

8. Import each edge of the helical path separately so that you now have two dwg files.
9. Select the topography element, select edit surface, and select Create from Import. Select one of the imported dwgs and you should see the topo be modified to follow the helical edge. Repeat for the other edge and as shown in steps 1, 2, and 3 in Figure 10.

Figure 10: Selection steps for helix

Soil Around a Retaining Wall

In this section you will be shaping existing topo to around the near and far side of a retaining wall.
1. Open your existing project or create a topo surface and a concrete retaining wall.
2. Create a new in-place mass and simply draw a curve where you would like the top of the soil to be located on the upper portion of the wall at the face of wall. Do the same for the lower portion of the soil. You should have two mass curves that are located in Figure 11.

Figure 11: Top of soil at high and low locations

Note: The divided nodes are used as a guide to place the topo surface nodes and they must be lined up horizontally in order to create the effect of the continuous topo surface being at two elevations.

3. To ensure that the divided nodes on each curve lines up horizontally you will need to locate the nodes via the “intersect” divided node command. To use this you have to draw gridlines (or named reference lines) at equal plan spacing. A good rule of thumb is to make at least 12 divisions/gridlines. Once the gridlines are placed at equal spacing select each curve separately and select the divide path command and select intersect and select the gridlines. The final divided node location should look similar to Figure 12.
4. Now that the divided nodes are in place, it’s time to place the topo points on top of the divided nodes. To modify the topo, simply change to a top down view in 3D and edit the topo and place points at each divided node. Change to a 3D side view and move the nodes vertically, in elevation, to the divided node.

Figure 12: Divided node and topo point locations

5. Finish the topo and a section thru your topo should look similar to Figure 13.
Note: In order for the soil to be retained at a different elevation on each side of the wall the topo surface has to be hidden within the concrete wall.

Figure 13: Section thru retaining wall

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About the Authors

Marcello Sgambelluri

Marcello Sgambelluri is the BIM Director at John A. Martin & Associates Structural Engineers in Los Angeles, CA. He has been using Autodesk products for more than 15 years including AutoCAD, 3ds Max, and Revit Structure. Marcello is devoted to helping advance the use and knowledge of BIM solutions within the AEC community. He frequently presents at Autodesk University and The Revit Technology Conference. He can be reached at marcellojs@johnmartin.com.