On occasion, a Civil 3D project may require data from a legacy drawing. This might be a DWG file for which you do not know or have the original authoring application. In cases like this, Civil 3D can recreate design data from drawing entities. In this session, we’ll learn how to build a surface model from selected objects.
On my screen is a drawing that represents some existing roadway conditions. The drawing itself has no underlying data. It’s simply a collection of individual AutoCAD entities that were exported from an unknown design application. Knowing that, I would like to leverage this existing ground surface data in a Civil 3D project. While reviewing the drawing, I found a layer called TIN. I’m going to turn this on. When I do, you can see it contains geometry representing the original surface model. If I hover over these segments, we can see that they are lines. Let’s isolate this geometry. In the Layers panel, I’ll click the Layer Isolate button, and then I’ll select one of the lines and press enter. I will then zoom out, and I’ll select this geometry. I’ll hold down shift and the mouse wheel, and we’ll orbit this up. I’ll zoom in and we’ll orbit some more. From here, we can see that the line segments are in 3D, so I can use these to create a duplicate of the original surface. When I’m finished reviewing the geometry, I’ll type PLAN and press enter twice to go back to a top view.
In addition to the triangulation, I’d also like to replicate the boundary around the outside of this geometry. Let’s do that. I’m going to type LINEWORK. This gives me access to the LINEWORKSHRINKWRAP command. LINEWORKSHRINKWRAP creates a boundary around selected objects. So, if I select all of these entities and press enter, you can see I get a polyline that surrounds them. That polyline is drawn on the current layer. To make this a little easier to see, I’m going to come over to the Properties palette, and I’ll change its color to red. I’ll press escape when finished.
Now that I know that I have some data to work with, I’m going to create a copy of this drawing. I’ll click save as, and I’ll call this LegacyFile-temp. This way I don’t disturb the original drawing. Likewise, since I’m working in a legacy file, I don’t have access to all of my Civil 3D styles and settings, so if you’ll indulge me for just a second, I’m going to go to the Manage tab. I’ll come down to the Styles panel, and I’ll click Reference. I would like to create a new reference to my company template file. I’ll click Open, and I’ll click Update. This will import all of my company settings and styles, such that I have something to work with when I create the surface.
To build the surface, I’m going to come back to the Home tab. I’ll open the Surfaces menu, and I’ll choose Create Surface. I’m going to call the surface EG for existing ground, and then we’ll select the Triangles Only style. I’ll click OK and OK. Once the surface is created, we’ll add data. I can do that by going to the Modify ribbon tab. I’d like to modify a surface. I’d like to add data, and that data will be drawing objects.
From here, if I open the Object Type menu, you can see all of the AutoCAD objects that can be leveraged as surface data. Feel free to come back and experiment with some of these others when you get a chance. For right now, I’m going to select Lines. Since I’m using lines, I am also going to choose Maintain edges from objects. I do this because Civil 3D is going to triangulate to the endpoints of each of these line segments. Selecting maintain edges will ensure the triangulation matches the connections defined by the geometry, giving me an exact copy of the original surface model. I’ll click OK. I will then select all of the line segments and press enter. If I zoom in and pan around, you can see that the new surface matches the original triangulation, with the exception of the outside edge.
Just for a second, I’m going to select the surface. I’ll right click and go to Display Order. We’ll send this to the back. I will then add this boundary we created earlier. Still in the Modify tab, I’d like to modify a surface. I’d like to add data. We’ll add a boundary. I’ll call this outside. I’ll keep the remaining default settings and click OK. Then I’ll select the polyline we created using the SHRINKWRAP command. If I back up, you can see the boundary now honors the original surface model.
Just for a second, let’s take a closer look at what we have. If I select one of these segments and the surface, I can also right click and choose Select Similar. To select all of the line segments, I’ll go to Object Viewer. And if we orbit this up, we can see that the new surface model matches the original triangulation perfectly. When finished reviewing the surface, I’ll close the object viewer, and I’ll press escape to deselect.
Now, I must admit, the first time I created a surface this way, I was tempted to go back and delete all of the original line segments. You can’t do that though, because without these line segments, you have no surface. That said, a data shortcut trick can be used to eliminate the unwanted entities. Let’s look at that. We’ll start by saving the temp drawing. Then we’ll go to the Manage tab and I’ll choose Create Data Shortcuts. I’ll create a data shortcut to the existing ground surface in this drawing. I’ll click OK. Here on the Prospector tab inside my current roadway project, we’ll find the new shortcut. Next, I’ll create a new drawing from the company template. I will then data reference that surface into this drawing. I’ll do that by selecting its shortcut from the project, and then I’ll drag and drop it into the file. I’ll keep the default name and style. We’ll click OK. I’ll double click the mouse wheel to do a zoom extents, and we can see the referenced surface data on screen.
Once the surface is referenced, I’ll select it and choose Promote Data Reference from the contextual ribbon. This creates a copy of the surface model in this drawing, leaving all of those unwanted AutoCAD entities behind. I will then press escape to deselect the surface. I now have an optimized version of the surface in this drawing, making the shortcut I created earlier obsolete. For that reason, I’m going to right click on that shortcut in the project and choose Remove. Next, we’ll save the current drawing. I’ll call it SurfaceModel, and I’ll click Save. And then I’ll create a new data shortcut that points to the surface in this file. I’ll do that by going back to Create Data Shortcuts. I’ll select the optimized surface, and then I’ll click OK to add the new shortcut to the project.
Finally, this surface, recreated from AutoCAD geometry, can easily be shared with any of my other design files. It’s been said that you can’t always get what you want. On occasion, that may mean having to extract design data from generic AutoCAD drawings. Fortunately, when the need arises, Civil 3D makes it easy to reverse engineer many design components from selected objects.