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AUTHOR: Steven Costa

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3D Printing a Civil 3D Surface

There’s an old saying that I’m sure you’ve heard that goes “you won’t know until you try”. While it’s one of those phrases that’s been around long before computers were in every office, it remains modern enough to be very relevant to working with software. I found myself thinking about this phrase when a client asked if they could have a Civil 3D surface printed on our 3D Printer, a 3D Systems CJP Project 660Pro.

It may sound obvious, but the only prerequisite for printing anything in 3D is that the object has a width, depth, and height. A Civil 3D surface object, while made up of X, Y, and Z points, is only a two-dimensional object since it has no thickness. The first hurdle would then be to add some “thickness” or height to that surface to make it printable.

If you are a Civil 3D user you may think, “well that’s easy, just use the Extract Solids from Surface”. And while that is exactly what crossed my mind when I started thinking about how to print a Civil 3D surface, it turns out that the Extract Solids from Surface does not work for very complex geometries. This command is great for extracting out solids from corridors and smaller surfaces, but it couldn’t generate a solid for a heavily graded 70-acre subdivision with 100’ of elevation difference between its low and high points.

As I didn’t have rights to use the surface described above when writing this blog, I am instead using another surface to illustrate the steps. For all intents and purposes, these steps will work for any surface.

Exporting Civil 3D Data for 3ds Max

Met with failure, I turned to 3ds Max, the most powerful geometry editing software in the AEC Collection. I had many options to choose from when importing the Civil 3D surface into 3ds Max, but I narrowed it down to two options.

The first option would use Civil View to exchange Civil 3D object data with 3ds Max using a VSP3D file. The second option is to export a LANDXML file from Civil 3D and then import that file into 3ds Max.

I ended up choosing the latter option since it automatically generated polygons in the various HIDE boundaries found on the Civil 3D surface I was using. While I lost a marginal amount of fidelity from the original surface, using LANDXML created a gapless surface which we preferred for the 3D Print.

Exporting a LANDXML file from Civil 3D is as easy as right-clicking the surface in the Prospector and selecting Export LandXML… Importing the LANDXML file into 3ds Max is equally simple; click on the File menu, choose Import and select the LANDXML file. You should uncheck Smooth Surface in the Object Creation Options to preserve the Civil 3D surface geometry.

Creating a watertight model

Unlike the Extract Solids from Surface command in Civil 3D, I simply had to create a watertight poly surface or mesh in 3ds Max. A watertight model is defined as an object that doesn’t have any naked edges. McNeel’s website makes a great analogy when defining a watertight object; “another way to understand a solid is to see it as a balloon. If there is even a pin prick size hole, it will deflate. Thus it is not air/watertight, not volumetric. A solid is a volume. A solid is its outer surfaces, once they are completely joined

The LANDXML import provides me with a editable mesh in 3ds Max. To manipulate the geometries in the mesh to create the watertight solid I previously mentioned, follow these steps:

  • Select the Editable Mesh and choose the Element sub-object levels in the modifier stack
  • Click on any part of the surface and you will see the entire mesh highlight
  • In the Edit Geometry rollout enter in an Extrude value; I will use 500’
  • Switch the to the Edge sub-object level and press the Select Open Edges button in the Edit Geometry rollout
  • With the open edges selected, toggle the Top view and select View Align from the Edit Geometry rollout. This will flatten the edges to the same Z value
  • Choose the Face sub-object level and drawing a Crossing Selection through the recently extruded faces
  • Select the Detach button from the Edit Geometry rollout to create new object from those faces
  • De-select the original mesh and select the detached mesh
  • Right-click and choose Convert To: Convert to Editable Poly from the Transform Quad
  • Select the Editable Poly object, activate its Border sub-object level, and select the open border
  • From the Graphite Modeling Tools, select Cap Poly from the Geometry (All) Panel in the Modeling ribbon
  • Activate its Polygon sub-object level and select the bottom polygon cap
  • Press the W key to activate the Move gizmo and raise the Polygon along the Z axis to the desired height
  • Deselect all sub-object levels, select the Editable Poly
  • Right-click and choose Convert To: Convert to Editable Mesh from the Transform Quad
  • De-select the detached mesh and select the original mesh
  • Select Attach from the Edit Geometry rollout
  • Choose the detached mesh to join it to the original mesh creating a watertight mesh

Despite the extensive list of steps, the process is straightforward if you are familiar with 3ds Max. The video below illustrates all these steps to make it easier to follow along.

Create a file for 3D Printing

Once the geometry has been edited to be watertight, export the geometry to an STL (STereoLithography) file. In order to send our 3D print jobs, we use an application called 3D Sprint. 3D Sprint can import the STL, check for any geometry errors, and scale the model so it can be printed. The screenshot below shows the 3ds Max geometry ready to be printed.

3d Sprint Civil 3D Surface

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Importing NOAA LIDAR scans with Autodesk Recap

The National Oceanic and Atmospheric Administration (NOAA) provides free access to their Data Access Viewer (DAV). The DAV allows users to search for and download various data types for the coastal U.S. and its territories. The data types available are elevation, imagery, and land cover data. This data can be useful on all phases of a design project, so let’s explore how to access LiDAR data for use in Autodesk applications that support point clouds.

Data Access Viewer (DAV)

NOAA’s Data Access Viewer (DAV) can be accessed via this link (https://coast.noaa.gov/dataviewer/#/) and can be used to access elevation, land cover, and imagery datasets for the coastal regions of the United States.
NOAA Elevation Limits in the USA

After selecting Elevation, zoom into or draw your area of interest (AOI). Alternatively, enter in an address or the coordinates of your project area. You can then see the available data for that region or range. I’ve drawn a region around Long Island City, NY for this example. For that AOI there are three DEM files (digital elevation models) and two LiDAR files are available.

NOAA Example Project limits for LiDAR NOAA 2014 Hurricane Sandy Lidar Scan Tile Limits

Finding LIDAR data

I’m interested in the latest LIDAR scan from the USGS and so I have one of two additional choices. I can use the bulk download feature to download the various tiles that make up my AOI. Alternatively, I can add my request to the cart and let NOAA’s servers process the request to only provide the points bound by my AOI. I will choose the latter which allows me to make additional changes to how I want to receive the data.

NOAA Cart Checkout LIDAR dataI want point cloud information, so I need to change the OUTPUT PRODUCT from Raster to Point. Additionally, I will verify the output format is an LAS file, a format that can be imported into Autodesk Recap. Lastly, I will verify that Data Classes include all points, not just the ground points. To wrap up, enter an email address to allow NOAA’s servers to contact you once the job is ready for download. Click the image on left to see these settings.

Importing the LAS file

The processing time for this job example took about 5 minutes to generate. Once you have received and downloaded your LiDAR scan you will want to import the LAS file(s) into AutoCAD ReCap. Processing the LiDAR scan in Recap allows you to use this scan in Autodesk products such as Civil 3D, Revit, Navisworks, Infraworks, and 3ds Max.

To begin, create and name a new Recap project by choosing a project name directory to store the project. Next, using Windows Explorer, browse to the LAS file(s) you extracted and drag-and-drop them onto Recap.

Dragging and dropping these files onto the target icon in ReCap will take you to a screen where you can change the Scan Settings.

Click on Advanced Settings. It’s important to note it is only at this point of the importing process that you can transform the LiDAR scan from its original coordinate system to your desired coordinate system.
Setting Coordinate System for Lidar Data in Autodesk Recap
Since the site is in Queens, NY, I will be using the NY State Plane Coordinate System NY83-LIF. This datum, (North American Datum 1983, Long Island Zone, US Survey Feet) is used for the 5 boroughs of NYC and Long Island. After setting the coordinate system, select, Import files, then index scans, and when the files are indexed, click Launch Project.
Long Island City Lidar Scan in Autodesk Recap
Once opened, save the project and you will have an RCP file you can link into products like Civil 3D, Revit, and Infraworks.
Revit Section Through LIDAR Scan Autodesk from Recap

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Ponding study in Civil 3D?

A recent question on the Civil 3D Forums had me wondering whether it was possible to display ponding water on a Civil 3D surface. I was certain there wasn’t a push-a-button-get-an-answer solution, but I decided to see if I could get the job done using a combination of Civil 3D tools.

To understand where ponding could occur on this surface, one would need to analyze the surface and identify which regions of the surface contain depressions where water could collect. Depending on how many local low points there may be on the surface, it’s likely that any analysis would need to be iterative and require a certain amount of user input.

While the solution I present below works for some Civil 3D surfaces, the actual question posted on the Civil 3D Forums asked about a large and complex DEM (digital elevation model). With that in mind, I will be making additional suggestions for complex analysis using another application better suited for the task in a separate blog post.

EXTRACT A DEPRESSION AREA

3D surface contours and triangles I’ll begin with a Civil 3D surface, one readily available with every installation of the product. The simplest way to do an analysis of the drainage areas of a surface is to run a watershed analysis. When running the analysis, I am only going to be focusing on the depressions on that surface. Once again, depending on your surface geometry, you may get one or more depressions, or you may get none. In the surface I am working with, there are six distinct depression areas, however I will be focusing in on the largest of the six for the purposes of this blog.

Once I have identified the depression I want to work with, the next step is to determine the lowest point on the edge of that depression since it will be the “spill over” point, that is, the point at which water will drain into the adjacent area on the surface. Again, there are several ways to accomplish this task, but I found the quickest non-lisp related way to find the lowest elevation point is to:

  1. Select the surface and use the Extract from Surface tool
  2. Next, select only Watersheds → Select Manually and choose the depression boundary, then press OK
  3. In model space, select the extracted 3D Polyline, right-click and choose Quick Profile
  4. Choose a basic Profile View style, select OK, and then select a point to place the Profile View
  5. Select the existing ground Profile, right-click and choose Profile Properties
  6. Make the Profile Data tab active and make note of the minimum elevation for the profile

Identify low point for ponding using watershed depressions

IDENTIFY THE SPILL-OVER ELEVATION

Once you have the minimum elevation of that boundary, you can then use that same extracted boundary edge to temporarily create an outer boundary for the surface you are analyzing. Doing so, and then examining the surface properties, would reveal the minimum elevation of the surface within that depression. This will give you the delta between the low point and the spill-over point. Alternatively, you could create a “zero elevation” surface and use the Minimum Distance Between Surfaces to find the low point on the EG surface.

Using the spill-over elevation, you can now create a user contour set to that elevation and style it for easy visibility. To do so:

  1. Select the surface, right-click and choose Surface Properties
  2. Select the Analysis tab and choose User-Defined Contours from the Analysis type drop-down menu
  3. Add one range and select Run Analysis
  4. Set the elevation of that user-defined contour to the spill-over value and press OK.

Using the spill-over limit, a pond surface can be created

STYLE THE USER CONTOUR

To see that contour on your surface you will need enable User Contours on the surfaces current style . We will then extract that contour as a polyline to use for our POND surface. To do so, follow these steps which are similar to the ones above:

  1. Select the surface and use the Extract from Surface tool
  2. Select only User Contours → Select Manually and choose the user contour within the depression boundary you are analyzing. If only one contour exists, Civil 3D will default to Select All.

I had to do some minor clean-up of the line-work in my example as there were some duplicate lines, but in the end, I now have a boundary representing my ponding limits. The last step is to create a surface called POND from the extracted polyline. You should use that polyline to define both the breakline elevations and the outer boundary of the surface.

VISUALIZE YOUR PONDING AREA

You can now use that surface to do any type of visualization that you would need. As an example, create a volume surface and run an elevation analysis to determine the depth/distribution of the ponding. See the image below for an example.
Volume surface showing depth and distribution of the ponding

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