Working with Survey Networks

Once you import survey data into a network, expand the branch to see how Civil 3D helps you make sense of it. In each network, data is organized by type, as shown in Figure 1.

Figure 1:  A typical survey database network with data.

Control Points

Control points are created when data from an FBK file is imported. Inside the FBK, control points are prefaced by NE, NEZ, or LAT LONG. You can force any point to be listed as a control point by right-clicking this collection and selecting New.

Non-Control Points

Keyed-in points, GPS-collected points, and any point brought in through an ASCII file will appear as non-control points. This is the default type if no other information is known about the point.

Directions

The direction from one point to another must be manually entered into the data collector for the direction to show up later in the survey network for editing. The direction can be as simple as a compass shot between two initial traverse points that serves as a rough basis of bearings for a survey job.

Setups

If you imported data that contains setups and observations, Setups is where the meat of the data is found. Every setup, as well as the points (side shots) located from that setup, can be found listed here. Setups will contain two components: the station (or occupied point) and the backsight. To see or edit the observations located from the setup, right-click Setups and select Edit Setups That Observe. Figure 2 shows the interface for editing setups. Backsight orientation and instrument heights can also be changed in this dialog.

Figure 2:  Setups can be changed in the Setups Editor.

Traverses

The Traverses section is where new traverses are created or existing ones are edited. These traverses can come from your data collector, or they can be manually entered from field notes via the Traverse Editor, as shown in Figure 3. You can view or edit each setup in the Traverse Editor, as well as the traverse stations located from that setup.

Figure 3:  The Traverse Editor.

Once you have defined a traverse, you can adjust it by right-clicking its name and selecting Traverse Analysis. You can adjust the traverse either horizontally or vertically, using a variety of methods. The traverse analysis can be written to text files to be stored, and the entire network can be adjusted on the basis of the new values of the traverse.

In the following exercise, you will adjust a traverse:

1. Create a new drawing from the _AutoCAD Civil 3D (Imperial) NCS.dwt or (_AutoCAD Civil 3D (Metric) NCS.dwt).
2. Navigate to the Toolspace ➢ Survey tab.
3. Right-click Survey Databases and select New Local Survey Database.
   The New Local Survey Database dialog opens.
4. Enter Traverse as the name of the folder in which your new database will be stored.
5. Click OK to dismiss the dialog.
   The Traverse survey database is created as a branch under the Survey Databases branch.
6. Expand the Traverse branch, right-click Networks, and select New.
   The New Network dialog opens.
7. Expand the Network branch in the dialog if needed.
8. Name your new network Traverse Practice and click OK.
9. Right-click the Traverse Practice network and select Import ➢ Import Field Book.
10. Select the file 0204_Traverse.fbk or (0204_Traverse_METRIC.fbk), which you can download from this blog, and click Open.
    The Import Field Book dialog opens.
11. Make sure you have checked the boxes shown in Figure 4.

    Figure 4:  The Import Field Book dialog.

    There is no linework in this file because it is just traverse shots.
12. Click OK. Double-click your middle mouse wheel to zoom extents to get a look at the imported traverse. The Traverse Practice network is now listed as a branch under Toolspace ➢ Prospector ➢ Survey ➢ Networks.
13. Save the drawing as 0204_Traverse.dwg for the next exercise.

Looking back at the Toolspace ➢ Survey tab, expand the network you created earlier and inspect the data. You have one control point in the northwest corner that was manually entered into the data collector. There is one direction, and there are four setups. Each setup combines to form a closed polygonal shape that defines the traverse. Notice that there is no traverse definition. In the following exercise, you’ll create that traverse definition for analysis.

Continue working in the drawing from the previous exercise:

1. Go to Toolspace ➢ Survey ➢ Survey Databases ➢ Traverse ➢ Networks ➢ Traverse Practice; then right-click Traverses and select New to open the New Traverse dialog.
2. Name the new traverse Traverse 1.
3. Type 2 as the Initial Station point number and press Enter.
   The traverse will now pick up the rest of the stations in the traverse and enter them in the next box.
4. Verify that the points on the traverse match what is shown in Figure 5.

   Figure 5:  Defining a new traverse.

5. Click OK.
6. Right-click Traverse 1 in the Item View of Toolspace. Select Traverse Analysis.
7. In the Traverse Analysis dialog, ensure that Yes is selected for Do Traverse Analysis and Do Angle Balance.
8. Select Least Squares for both Horizontal Adjustment Method and Vertical Adjustment Method.
9. Set both Horizontal Closure Limit 1:X and Vertical Closure Limit 1:X to 20,000.
10. Leave Angle Error Per Set at the default.
11. Make sure the option Update Survey Database is set to Yes.
    The Traverse Analysis dialog will look like Figure 6.

    Figure 6:  Specify the adjustment method and closure limits in the Traverse Analysis dialog.

12. Click OK.

The analysis is performed, and four text files are opened that show the results of the adjustment. These files are automatically saved in the survey working folder under the same directory as the survey database (in this example, it should be C:\Civil 3D Projects\Traverse\Traverse 1\).

Note that if you look back at your survey network, all points are now control points because the analysis has upgraded all the points to control point status. Also, error ellipses are displayed in the drawing area at each station adjusted. The size of error ellipses are controlled by a scale factor set in the Survey Network style. If you are seeing extra-large ellipses, it is not an indication of an extra-large error.

Figure 7 shows the Traverse 1 Raw Closure.trv and Traverse 1 Vertical Adjustment.trv files that are generated from the analysis. The raw closure file shows that your new precision is well within the tolerances set in step 8. The vertical adjustment file describes how the elevations have been affected by the procedure.

Figure 7:  Horizontal and vertical traverse analysis results.

Traverse 1.lso is the output file displaying the adjustments of the traverse analysis. The first part of the file, shown in Figure 8, displays the various observations along with their initial measurements, standard deviations, adjusted values, and residuals. You can view other statistical data at the beginning of the file.

Figure 8:  Statistical and observation data portion of text file.

Figure 9 shows the second portion of this text file (you will need to scroll down to see it) and displays the adjusted coordinates, the standard deviation of the adjusted coordinates, and information related to error ellipses displayed in the drawing. If the deviations are too high for your acceptable tolerances, first check the instrument settings and tolerances in the equipment database. If everything is set correctly, you may need to redo the work or edit the field book.

Figure 9:  Adjusted coordinate information portion of text file.

Figure 10 displays the final portion of this text file—Blunder Detection/Analysis. Civil 3D will look for and analyze data in the network that is obviously wrong and choose to keep it or throw it out of the analysis if it doesn’t meet your criteria. If a blunder (or bad shot) is detected, the program will not fix it. You will have to edit the data manually, whether by going out in the field and collecting the correct data or by editing the FBK file.

Figure 10:  Blunder analysis portion of text file.

Traverse 1.lsi is the input file for displaying the station-to-station observations of the traverse analysis. This file can be edited and used to rerun the analysis based on the revised observations.

You can compare the final result against the completed file as the name 0204_Traverse_FINISHED.dwg or (0204_Traverse_METRIC_FINISHED.dwg).

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Understanding the Survey Database

• Working with Survey Networks
• Other Methods of Manipulating Survey Data