Lesson Note On Civil 3D Building a Surface

Building a Surface

To build a surface

1. Create a new surface if needed. For more information, 

2. Add surface data to the surface folders if you haven't already.

3. From the Terrain menu, choose Terrain Model Explorer.

4. Right-click on the surface folder, for example to display the shortcut menu.

5. Click Build to display the Build Surface dialog box.

6. Click the Surface tab if it is not already active.

7. In the Description box, you can type a description for the surface. The surface description can be up to 255 characters.

8. Select one or more of the following options to control how the surface is built:

• Log Errors to file: Select this check box to create a <surface name>.err file in the following folder:

c:\Land Projects <Version Number>\<project name>\dtm\<surface name>

This log file records the time it takes to build the surface, and records each step that the Build Surface command performs, such as adding point files or point groups to the surface.

• Build Watershed: Select this check box to build a watershed at the same time the surface is built. If you select this option, then be sure to click the Watershed tab and set up the watershed options.
• Compute Extended Statistics: Select this check box to generate extended surface statistics. These statistics are displayed when you click the surface name, for example in the Terrain Model Explorer.

9. Select any of the following surface data options to control how surface data is processed:

• Use point file data: Select this check box to build the surface using the data in the surface's folder. If you clear this check box, then the surface is built without the point file data.
• Use point group data: Select this check box to build the surface using the data in the surface's folder. If you clear this check box, then the surface is built without the point group data.
• Use DEM File data: Select this check box to build the surface using the DEM file data in the surface's folder. If you clear this check box, the surface is built without the DEM file data.

NOTE Building a surface using DEM files that contain large numbers of points can use significant system resources, especially if the "Build Watershed" check box is selected.

• Use breakline data: Select this check box to build the surface using the data in the surface's folder. If you clear this check box, then the surface is built without the breakline data.
• Convert proximity breaklines to standard: Select this check box to convert proximity breaklines to standard breaklines when the surface is built. Proximity breaklines obtain their exact point location and elevation by snapping to the nearest point on the surface. If you convert proximity breaklines to standard breaklines when building the surface, the breaklines are saved with fixed locations and elevations. Therefore, if any of the surface point data that the proximity breaklines were snapping to is subsequently changed, the breaklines are not updated with these changes.

When a proximity breakline is converted to a standard breakline, one or more standard breaklines are added to the breakline file in the Terrain Model Explorer, each with the description of the breakline from which it was converted.

Clear this check box if you want to preserve proximity breaklines when building the surface.

• Use contour data: Select this check box to build the surface using the data in the surface's folder. If you clear this check box, then the surface is built without the contour data.
• Minimize flat triangles resulting from contour data: When building a surface, select this check box to check each contour in the surface for any triangles that have three points at the same elevation. The program attempts to remove any such triangle by flipping faces. 
• Apply boundaries: Select this check box to build the surface using the data in the surface's folder. If you clear this check box, then the surface is built without the boundary data.
• Apply Edit History: Select this check box to apply the Edit History to the surface after it is built. The Edit History records all the surface editing that you have performed. For example, if you built a surface and edited it, but need to build it again, you do not have to make all the edits that you made previously. Just select the Apply Edit History check box and the edits repeat automatically.
• Don't add data with elevation less than: Select this check box to exclude any surface data that has an elevation less than the elevation you type in the box.
• Don't add data with elevation greater than: Select this check box to exclude any surface data that has an elevation greater than the elevation you type in the box.

10. If you selected the Build Watershed check box, then click the Watershed tab.

11. In the Minimum Depression Depth box, type the minimum depth at which a depression in the surface is to be considered a watershed. This setting prevents minor depression depths from being defined as watershed subareas.

12. In the Minimum Depression Area box, type the minimum area at which a depression in the surface is to be considered a watershed. This setting prevents minor depression areas from being defined as watershed subareas.

13. Select or clear the Must Exceed Both Minimum Area And Minimum Depth check box:

• Select this check box to create watershed subareas of only those depressions that exceed both the minimum area and the minimum depth.
• Clear this check box to create watershed subareas of those depressions that exceed either the minimum area or the minimum depth.

14. Click OK to build the surface.

A message dialog box is displayed, informing you that the program has finished building the surface.

15. Click OK.

16. If you want to view and edit the surface triangulation, then Import 3D Lines into the drawing. 

Lesson Note On Civil 3D Creating Contours From a Surface

Creating Contours From a Surface

To create contours from a surface

1. Build a surface. 

2. From the Terrain menu, choose Create Contours to display the Create Contours dialog box.

3. From the Surface list, select the surface that you want to create contours for. If the surface name is not displayed in the list, then click Browse to search for it. Surfaces have the file extension .tin.

4. Under Elevation Range, define the range of the surface's elevation for which to create contours by entering values in the From and To boxes. The low and high elevations of the surface are displayed as defaults.

TIP If you change the Elevation Range, then you can return to the default range by clicking the Reset Elevations button.

To exaggerate the elevational changes of the contours when you look at them in 3D, enter a value other than 1 in the Vertical Scale box.

NOTE If you exaggerate the vertical scale, the contours are drawn at an exaggerated elevation and are therefore incorrect when labeling or as a basis for future TIN creation.

5. Under Intervals, select one of the following options:

• Both Minor and Major
• Minor Only
• Major Only

6. Define the contour intervals by entering values in the Minor Interval and Major Interval boxes. For example, if you enter a minor interval of 2, and your drawing units are meters, then a minor contour is created every place there is a 2-meter change in elevation.

7. Specify the layers for the major and minor contours. By placing the minor and major contours on different layers, you can easily control the contour colors and linetypes. You can select a layer or type in a new layer name.

8. Under Properties, select one of the following options:

• Contour Objects: To create contour objects. 
• Polylines: To create polyline contours.

NOTE If you select the Polylines option, then you cannot select a contour style to use.

9. From the Contour Style list, select the contour style to use for the contours.

TIP Click the Preview button to see a preview of the contour style.

10. If you need to load a contour style, edit a style, or create a new style, then click the Style Manager button to display the Contour Style Manager dialog box.

11. Click OK to generate the contours.

The following prompt is displayed:

Erase old contours (Yes/No) <Yes>:

12. Type Yes or No:

• Type Yes to erase any existing contours that may be present on the contour layers.
• Type No to preserve existing contours.

WARNING! If you type Yes to erase the old contours, then existing contours on both the major and minor contour layers are erased. When you develop grading plans, pay attention to the layers that the Create Contours command uses so that your existing ground contours are not erased. 

Lesson Note On Theodolite/EDM Topographic Survey

How To Used Theodolite/EDM Equipment

 Theodolite/EDM Topographic Survey

Description: Using EDM instruments and optical or electronic theodolites, locate the positions and elevations of all topographic detail and a sufficient number of additional elevations to enable a representative contour drawing of the selected areas. See sample field notes in Figure D.9.

Equipment: Theodolite, EDM, and one or more pole-mounted reflecting prisms.

Procedure:

• Set the theodolite at a control station (northing. easting, and elevation known), and backlight on another known control station.

• Set an appropriate reference angle (or azimuth) on the horizontal circle (e.g., 0°00'00" or some assigned azimuth).

• Set the height of the reflecting prisms (HR) on the pole equal to the height of the optical center of the theodolite/EDM (Hi).

• Prepare a sketch of the area to be surveyed.

• Begin taking readings on the appropriate points. Entering the data in the field notes (Figure D.9) and entering the shot number in the appropriate spot on the accompanying field-note sketch. Keep shot numbers sequential, perhaps beginning with 1,000. Work is expedited if two prisms are employed. While one prism-holder is walking to the next shot location. The instrument operators can be taking a reading on the other prism-holder.

• When all field shots (horizontal and vertical angles and horizontal distances) have been taken, sight the reference backsight control station again to verify the angle setting; also, verify that the height of the prism is unchanged.

• Reduce the field notes to determine station elevations and course distances, if required.

• Plot the topographic features and elevations at scales.

• Draw contours over the surveyed areas. 

Lesson Note On Total Station Topographic Survey

How to used total station

Total Station Topographic Survey

Description Using a total station and one or more pole-mounted reflecting prisms, plot all topographic features and any additional ground shots that are required to accurately define the terrain. See Figure D.l0.

Equipment:Total station and one, or more, pole-mounted reflecting prisms.

Procedure:

• Set the total station over a known control point (northing, easting, and elevation known).

• Set the program menu to the type of survey (topography) being performed and to the required instrument settings. Select the type of field data to be stored (e.g., N, E, and Z, or E, N, and Z, etc.). Set the temperature and pressure settings-if required.

• Check configuration settings, for example, tilt correction, coordinate format, zenith vertical angle, angle resolution (e.g., 5"), c + r correction (e.g., no.), units (ft/m, degree, mm Hg), and auto power off (say, 20').

• Identify the instrument station from the menu. Insert the date, station number coordinates, elevation, and Hi.

• Backsight to one or more known control point(s) (point number, north and east coordinates, and elevation known). Set the horizontal circle to 0°00'00" or to some assigned reference azimuth for the backsight reference direction. Store or record the data. Measure and store the reflector height.

• Set the initial topography point number in the instrument (e.g., 1,000), and set for automatic point number incrementation.

• Begin taking I.Ss. Most total stations have an automatic mode for topographic surveys, where one button-push will measure and store all the point data.

• Put all or some selected point numbers on the field sketch. These field notes will be of assistance later in the editing process if mistakes have occurred.

• When all required points have been surveyed, check into the control station originally back sighted to ensure that the instrument orientation is still valid.

• Transfer the field data into a properly labeled file in a computer.

• After opening the data processing program, import the field data file and begin the editing process and the graphics generation process.

• Create the TIN (Triangulated Integrated Network) and Contours.

• Either finish the drawing with the working program or finish it on a CAD program.

• Prepare a plot file and then plot the sheet on scale.

Reference: Surveying with Construction Applications Seventh Edition

Barry. F. Kavanagh pages: 616-620 

LESSON NOTE ON DTM

What is a DEM (Digital Elevation Model)?
Digital Elevation Models are data files that contain the elevation of the terrain over a specified area, usually at a fixed grid interval over the surface of the earth. The intervals between each of the grid points will always be referenced to some geographical coordinate system. This is usually either latitude-longitude or UTM (Universal Transverse Mercator) coordinate systems. The closer together the grid points are located, the more detailed the information will be in the file. The details of the peaks and valleys in the terrain will be better modeled with a small grid spacing than when the grid intervals are very large. Elevations other than at the specific grid point locations are not contained in the file. As a result peak points and valley points not coincident with the grid will not be recorded in the file.
The files can be in either ASCII or binary. In order to read the files directly you must know the exact format of the entire file layout. Usually the name of the file gives the reference location to some map corner point in the file. The files usually contain only the z value (elevation value) and do not contain the actual geographical location that is associated with that point. The actual location associated with that elevation data is calculated by software reading the actual DEM file, knowing the precise location of the data value inside the DEM file. In addition, there will be some needed reference information in the header (first part) of the file. When an elevation is calculated at locations other than the actual grid points, some method of interpolation from the known grid points is used. Again, this is done in software that is external to the actual DEM file.
The DEM file also does not contain civil information such as roads or buildings. It is not a scanned image of the paper map (graphic). It is not a bitmap. The DEM does not contain elevation contours, only the specific elevation values at specific grid point locations.

Some companies chose to encrypt their DEMs, thereby prohibiting you from making your own files, converting data from other sources or allowing you access to data files that were provided from anyone other than that software vendor. SoftWright maintains an open architecture on all our data files. Details for all DEM file formats that SoftWright supports are available to any of our customers. 

LESSON NOTE ON CHECK ON CLOSED TRAVERSE

CHECK ON CLOSED TRAVERSE

1. Check on angular measurements

(a) The sum of the measured interior angles should be equal to (2N – 4) x 90⁰ where N is the number of sides of the traverse.

(b) The sum of the measured exterior angles should be equal to (2N + 4) x 90⁰.

(c) The algebraic sum of the deflection angles should be equal to 360⁰.

Right-hand deflection is considered positive and left-hand deflection negative.

2. Check on linear measurement

(a) The lines should be measurement once each on two different days (along opposite directions). Both measurements should tally.

(b) Linear measurements  should also be taken by the stadia method. The measurements by chaining and by the stadia method should tally.

LESSON NOTE ON CHECK ON OPEN TRAVERSE

CHECK ON OPEN TRAVERSE

In open traverse, the measurements cannot be checked directly. But some field measurements can be taken to check the accuracy of the work. The methods are discussed below.

1. Taking cut-off lines Cut-off lines are taken between some intermediate stations of the open traverse. Suppose ABCDEF represents an open traverse. Let AD and DG be the cut-off lines. The lengths and magnetic bearings of the cut-off lines are measured accurately. After plotting the traverse, the distances and bearings are noted from the map. These distances and bearings should tally with the actual records from the field

2. Taking an auxiliary point Suppose ABCDEF is an open traverse. A permanent point P is selected on one side of it. The magnetic bearings of this point are taken from the traverse stations A,B,C,D, etc. If the survey is carried out accurately and so is the plotting, all the measured bearings of P when plotted should meet at the point P. The permanent point P is known as the ‘auxiliary point’