CAD Clinic: Civil 3D -- Implementing Surface Object Styles

7 Oct, 2006 By: Phillip Zimmerman

Learn how to create and use slope and elevation analytical styles.

In the last article on surface styles, I discussed creating a style for building a surface. The style displays the surface's border, points and triangles. In this article I'll discuss creating and using slope and elevation analytical styles.

When creating a surface object style, the Surface Style dialog box contains controls and settings for all of the surface components. Each style uses only a subset of all the controls and settings (figure 1).

Figure 1. The Surface Style dialog box.

Slope and Slope Arrow Analysis Style
This style uses only two panels of the Object Style dialog box: Analysis and Display. The Analysis panel sets the defaults for each analysis you want to perform on surface data: directions, elevations, slopes and slope arrows (figure 2).

Figure 2. Slope analysis style settings.

Each property of a section affects how the style functions: Group by, Range Precision, Scheme, and Slope or Slope Arrows Display Mode.

Group By
The Group By property has three possible values: Equal Interval, Standard Deviation and Quantile. Equal Interval calculates a range value by dividing the difference between the lowest and highest values by the number of ranges. Standard Deviation is much the same, but based on the amount a value is statistically away from the mean or average. Quantile ranges data by creating groups with equal membership. The strategy that Quantile uses places extreme values in ranges with more members and is an effective method of group values when working with skewed distributions.

When working with surface slopes, their statistics are representative until introducing a wall breakline, or breaklines representing a wall. In figure 3 the image on the left side shows a typical surface slope report. The right side of figure 3 shows what happens to the slope statistics when a wall breakline is added to the surface. The wall breakline has such a high slope value that it biases the slope statistics to the high end. For example, in figure 3 without the wall, the surface average slope is 6.52%. With the wall breakline the average slope is almost 300% -- a significant statistical change.

Figure 3. Surface slope statistics reports.

If grouping surface slopes by Equal Interval, the difference is 350,000 divided by 8 ranges, making each range 43,750. This means the first slope range is 0-43750 and includes the entire surface except for the wall itself. The Standard Deviation method yields similar results.

The Quantile method produces completely different results. There are more slopes at the lower end, and as a result more ranges at this end of the data. The higher end has a broad range value to create a range with an equal number (200-350,000). By using this ranging method, the distribution of slopes is more meaningful (figure 4).

Figure 4. Slope ranges with the Quantile method.

Range Precision
If one range stops at 2 and the next range starts at 2, when a value is 2 what range does it go to? The function of range precision is placing a border value in a range. If the precision is set to 0.0001, a value greater than this is placed in the second range, and a lower value put in the first range. So, the slope value of 2.001 goes to the second range and 2.00009 goes to the first group.

The Scheme property sets the colors each range uses.

Display Mode
The Display mode sets the elevations the objects use in the drawing. The objects can be at their actual elevations, flattened to a user-specified elevation, or exaggerated by a user-specified value.

Display Settings
For a slope analysis style to display its results, the components it uses must be visible. The Display panel contains the settings for the components the style uses: Slope and Slope Arrows. You must manually toggle them on. The slope and slope arrows do not use a layer in the drawing (figure 5).

Figure 5. Slope and Slope Arrows display settings.

Elevation Analysis Style
What does the surface look like? Where are the high and low elevations? How do I communicate a surface to someone who cannot read contours? A surface analysis style answers all of these questions, and the model it makes is one of the best communicators for those challenged by reading contour lines on paper.

The settings and values making an elevation object style are the same as those for a slope or slope arrow style. The only values you may have to adjust are the number of ranges and exaggeration for the model, if you want any (figure 6).

Figure 6. Elevation analysis style settings.

Elevation Display Settings
The settings and values of the Display panel need to reflect the elevation focus of the style (figure 7). The settings are the same for 2D and 3D view directions.

Figure 7. Elevation display settings.

Using Analysis Styles
Assigning an analysis style to as surface does not cause the surface to calculate the analysis results. Civil 3D treats the analysis style as a set of defaults, and you must create the analysis for the surface. This is done in the Surface Properties Analysis panel (figure 8).

Figure 8. The Surface Properties Analysis panel.

At the top of the panel, you set the type of analysis and legend. In the center left is the range number (from the style), and the blue down arrow to the right, which when selected actually does the analysis calculation. The results of the calculation (by changing the range values from the default settings) appear at the bottom of the dialog box. After calculating the initial range values, you can manually change the range values at the bottom and Civil 3D recalculates the values for the new range limits; e.g., a range from 1.45% to 2.578% is changed to 1.5%-2.5%, or an elevation range from 723.4889 to 725.1234 to 723-725.

The results for these types of styles go a long way toward communicating the complexity and problems a designer may face when starting an engineering project (figures 9 and 10).

Figure 9. Slope analysis of a site.

Figure 10. Elevation analysis of a site.

Communicating the current state or proposed site design is critical to the success of a project. The function of the analysis styles is to inform and communicate ideas and designs, as well as show and explain existing conditions and design results. A slope style is a tool to show current conditions and challenges for existing conditions, and also a way to evaluate the quality of a proposed solution. An elevation style facilitates the communication of design results or the challenges of the current conditions. Analytical styles are important tools for any project.

The next installment will review a contour object style and begin the discussion on creating label styles for surfaces. The labels styles present the greatest challenge to implementing Civil 3D.

About the Author: Phillip Zimmerman

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