Unit 2 – Lesson 3: Surfaces Civil 3D 2010 Student Workbook ▪ 1 Surfaces Overview In this lesson, you learn how to work with surfaces in AutoCAD Civil 3D. Surfaces are three-dimensional objects used to represent both existing and proposed terrain conditions. The display of a surface is controlled with a surface style. Surfaces can be displayed with different components including contours, triangles, and points. Surfaces can also be annotated with contour elevations, spot elevations, and slopes. Engineers usually display existing terrain surfaces on their plans with contours. During the design process, engineers regularly work with existing terrain surfaces. These surfaces are used to check the interaction between the proposed design and the existing terrain. Engineers also create surfaces representing proposed conditions during the design process. These surfaces are used to help visualize the design, calculate material quantities, and to generate data required for construction staking. Lesson 3 AutoCAD Civil 3D 2010 Education Curriculum Student Workbook Unit 2: Create Ground DataUnit 2 – Lesson 3: Surfaces Civil 3D 2010 Student Workbook ▪ 2 Objectives After completing this lesson, you will be able to: - Describe surfaces. - Describe how breaklines are used for surface modeling. - Create a surface from points and breaklines. - Create and apply surface styles. - Apply contour, slope and spot elevation labels to a surface. - Export a surface to Google Earth. Exercises The following exercises are provided in a step-by-step format in this lesson: 1. Create a Surface 2. Modify Surface Properties 3. Edit a Surface 4. Create Surface Styles 5. Assign a Contour Style and Apply Surface Labels 6. Export a Surface to Google Earth Introduction to Surfaces Surfaces are the basic building blocks in Civil 3D. You use surface objects to create a three-dimensional representation of existing and proposed project data. A Triangulated Irregular Network, or TIN, is a surface model consisting of data points (vertices) connected by 3D lines (TIN lines) to form three-dimensional irregularly shaped triangular faces. These triangular faces are collectively called a TIN. TINs are used to model existing ground surfaces, proposed surfaces, subsurfaces (like bedrock), and water surfaces. By connecting surface points with a network of triangulation lines, you create a dynamic, continuous representation of a surface. Using this network, you can interpolate the elevation of any location on the surface, not just locations that are defined by a point. The TIN models a continuous surface that you can use to display contours and elevation data, and create surface profiles and targets for slope daylighting.Unit 2 – Lesson 3: Surfaces Civil 3D 2010 Student Workbook ▪ 3 A surface representing an existing intersection is shown in the following illustration: When you use a surface to create an existing ground profile for an alignment, or an existing ground cross section, the data points for the profile (station and elevation) and the data points for the cross section (station and offset) are generated where the alignment or cross section sample line interest the triangulation lines. Furthermore, contours are generated by connecting the points on the triangulations lines that have the same elevations. It is therefore very important to ensure that the triangulation lines are generated in the correct locations and connect to the correct points. You can read more about this topic in the section on breaklines. In the following illustration, note how the triangulation lines provide the “shape” for the contours. Also notice how the contours connect common elevations on the TIN lines.Unit 2 – Lesson 3: Surfaces Civil 3D 2010 Student Workbook ▪ 4 You can create two types of surfaces. Regular surfaces are used to model existing and proposed terrain. You use volume surfaces to calculate site volumes by referencing an existing and a proposed surface. The following illustration shows the Civil 3D interface for creating a TIN volume surface: When you create surfaces, you should keep the following important points in mind: - When creating surfaces from point data, points that do not represent the topography should be excluded from the surface model to ensure the accuracy of the surface. Examples of points to exclude include manhole inverts, hydrant tops, and raised manhole lids. You can use the exclusion criteria in a point group to exclude certain points from the surface model. - If the surface contains terrain breaks, breaklines must be defined to accurately represent the terrain breaks on the surface. Examples of Surfaces Surfaces can be used to model both existing and proposed conditions. You use surfaces that represent existing conditions to: - Display base mapping contours. - Generate surface profiles for alignments. - Generate surface sections.Unit 2 – Lesson 3: Surfaces Civil 3D 2010 Student Workbook ▪ 5 - Calculate volumes when compared against a proposed surface. - Calculate grading limits for corridors and grading objects. You use surfaces that represent proposed conditions to: - Display proposed contours. - Calculate volumes when compared against an existing surface. - Generate construction staking data. - Label design spot elevations and grades. About Breaklines Breaklines are required for most surface modeling tasks. Surface triangulation lines follow along the defined breaklines. It is important that triangulation lines follow the terrain breaks in order to accurately model the terrain. When you define a breakline, the surface lines follow the breakline instead of interpolating an elevation for the location using the closest points. Breaklines increase the accuracy of the surface because they interpolate elevations between two consecutive points along a distinctive terrain break. Adding a breakline improves the three-dimensional representation of linear features on the surface. Types of Breaklines The two most common types of breaklines defined in AutoCAD Civil 3D are proximity breaklines and standard breaklines. You choose the breakline type based on the type of polyline, 2D or 3D, being defined as a breakline. Proximity Breaklines Proximity breaklines are defined from 2D polylines. Elevations and locations of breakline vertices are determined by physically relocating each vertex of the 2D polyline to the nearest point used to create the
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