Surfaces

Behind corridors, surfaces are probably one of the most complex objects in Civil 3D. There are so many ways to define and edit a surface, if you haven’t worked with them, why not? Surfaces are the basis of so much in Civil 3D. We create profiles and sections from them, they display contours and labels, and we can analyze them in so many ways. They are just so versatile.

There are three types of surfaces in Civil 3D: TIN surfaces, Grid surfaces, and Volume surfaces. In this post, I want to talk about TIN surfaces; how to generate them, add, edit and remove data, and how to run the various analyses on them.

To get started, surfaces are located in the Prospector tab of the Toolspace palette. Under the current drawing, there is a section for Surfaces. If your drawing has a surface in it, the Surfaces collection can be expanded to list them. Let’s start by looking at the data that makes up a surface.

A surface is made up of a large variety of data, and is different for each surface type. A TIN surface is made up of a wide range of data that helps, essentially, to create points and triangles between these points. These points and triangles are the basis for all TIN modeling. TIN is an acronym for Triangulated Irregular Network, and you can read more about TIN and the underlying principles here. A key note to be aware of, is that a TIN cannot have two points that exist in the same X,Y coordinate. The algorithms that generate the lines between each point in the TIN get extremely confused as to what those points should connect to, therefore, if you need to model a vertical face, there should be a small offset between the vertical locations. I generally accomplish this with a 0.05′ offset, but it can be more or less, depending on your situation and required accuracy.

In order to create the points and lines of a TIN surface, Civil 3D has provided us with many options. One option is to add points and lines to the surface, using the Add Point or Add Line commands. These points and lines are permanently added to the surface, and can only be modified or removed using the Move Point, Modify Point, Delete Point, Delete Line and Swap Edge commands. Each of these commands will only work if the surface style is set to display the points or lines. Attempting to use these commands on a surface that does not will result in a dialog box informing you that you need to turn them on. These commands can be extremely difficult to use, and I would suggest using them sparingly. The more robust ways to edit a surface are to use other drawing objects that you can more easily manipulate.

As seen in the screenshot above, there are a lot of things you can add to a surface. The most common would be Breaklines. After breaklines, you have contours, DEM files, Drawing objects, Point Files, Point Groups and Point/Figure Survey Queries.

Breakline

A breakline is a 3d feature that will act as a feature that tells the surface to add points and lines along it’s length. Breaklines can be 3d polylines, feature lines or survey figures. You also have the option of adding supplementing factors to the breakline – such as add points along the line at intervals or along the curves based on a mid-ordinate distance. A breakline can also be weeded to remove points under a specific distance apart, or with a maximum angle deflection from each other.

Contours

Contours can be 2d or 3d objects, such as polylines or lines. Typically you would use a 2d object with elevations set to represent the contours. As with breaklines, you can define some weeding and supplementing factors when adding the contours to the surface. You’re also able to add a special edit to the surface in order to minimize flat areas once the contours are added. Keep in mind, this edit is added to the surface after each set of contours is added.

DEM Files

DEM files are external GIS files that store elevation data. The formats that Civil 3D can read are USGS DEM files (*.dem), GeoTiff files (*.tif), and ESRI ASCII/Binary Grid files (*.asc, *.txt, *.adf). These files generally have a geolocation and coordinate system associated with them and should be translatable to your working coordinate system.

Drawing Objects

This group of definition items allows for some more rudimentary Autocad objects to be used for surface data. The objects you can use are: Points, Lines, Blocks, Text, 3D Faces and Polyface. When adding these objects to the surface, you can specify a description so that you can more easily organize and find the objects in the surface definition. If an object is a linear feature (such as lines and 3D faces) you have the additional option to maintain edges from the object, which forces the lines to be held when the surface is triangulating between the points of the objects.

Point Files

These are external text files that contain location and elevation data. If you’ve worked with points provided by a survey outside of Civil 3D, you’ve likely seen a variation of a point file. The file can be formatted in one of many common formats, or you can create your own format. The benefits of using a Point File are that if the survey is updated with additional points, simply adding them to the file will update the surface.

Point Groups

A point group uses points that are added to the drawing. Typically, if you import the point file above, the points are static in your drawing file and can be added to the surface. The benefit of using the Point Group is that you can create a group that includes or excludes certain points and gives you more flexibility over what is used in your surface creation.

Point Survey Queries / Figure Survey Queries

These queries require a survey database to be created and open for your project. These methods allow you to store survey data in a centralized database for the project, which can be updated throughout the project life cycle. When using queries, if data is added to the database, the additional data will be brought into your file (if applicable) and the surface will be updated accordingly.

Boundaries

I skipped over listing boundaries earlier, because they aren’t so much ways to define the TIN as they are ways to limit the data being presented. A boundary can be any closed 2d or 3d object, such as a polyline or feature line. There are four types of boundaries that can be used: Outer, Show, Hide, and Data Clip. The Outer boundary is used to limit the extents of your surface, and will keep any triangles on the ‘outside’ of the boundary from being displayed. The Show boundary will allow any triangle that crosses inside of the closed area to be shown, while the Hide boundary does the opposite and removes any triangles within it’s closed area. A Data Clip boundary is used when you want to limit any data added to the surface to within an area.

With the exception of the Data Clip, each boundary option provides an option to create a Non-Destructive Breakline. When using this option, if a triangle crosses the boundary, it is clipped at that crossing.

Edits

The Raise/Lower Surface command is a quick way to adjust the entire site by inputting a positive (for raising) or negative (for lowering) number when prompted after selecting the edit. It is important to note that this edit does not affect the data used to create the surface, only the surface itself.

The Smooth Surface edit is a powerful edit tool that allows you to add additional points to the surface between breaklines and other base data. Smoothing uses one of two mathematical algorithms, Natural neighbor interpolation (NNI) and the Kriging Method. The NNI method is more straight-forward and allows for additional points to be added based on a grid pattern in an area of the surface or by adding points to specific triangles or edges in the selected area. Kriging method is an extremely advanced concept, and if I would suggest reading up more on Kriging if you would like more information on that method.

The Paste Surface edit allows you to combine one or more surfaces into another surface. When pasting surfaces, it is good to know that the surfaces are listed in a top-down order and the surface listed at the bottom (pasted last) will be overwrite any data of the surface above.

The Simplify Surface command is a great tool to use for removing unwanted data from a surface. The command has two options, Edge Contraction and Point Removal. Edge Contraction allows you to remove points of a triangle in order to minimize triangle edges, while Point Removal allows you to weed out points based on a margin of elevation differences. This edit command is great for simplifying large data sets like point clouds or DEMs.