Tutorial 5 – Traverse Entry & Adjustment

 

In this Tutorial you will learn how to

 

¨       enter a traverse using observed bearings

¨       check the misclose and accuracy of the traverse

¨       adjust the traversestore the adjusted coordinates into a database

 

 

From Windows, select the Start button, and then select Programs to see the list of available programs. Select Ezicad, and the Ezicad screen will appear.

 

Pull down the File menu and select New. Enter a Filename of ‘Traverse.CDSdb’, and a Description of Traverse Tutorial,  then select Open, and a blank screen will appear.

Access the Traverse Entry Screen

Use your mouse to select Entry from the options on the menu, and then select Traverse Network.

 

The screen will appear similar to that below left.

 

Since this is a new job, select the New option, and then maximise the screen so it appears as see on the right

 

At this stage you need to be aware that traverses are broken into two main groups, defined by how the horizontal angular measurement has been observed and recorded, and these are.

horizontal bearings

horizontal angles

 

If you use bearings in the field, please follow through the next section.

If you read angles between the adjacent traverse legs then unfortunately we haven’t yet written about that method.

Entering the Traverse with Observed Bearings

If you are in the habit of observing bearings in the field, then all you need do to get your traverse into the entry screen is to provide a STN record defining the coordinates (either real or adopted) of the first point in the traverse, and then enter the details of the individual legs.

 

In this exercise, the field party has carried out a closed traverse around a parcel of land, starting from Point 1, which has local coordinates of East 2500 North 1555, and R.L of 200.00.

 

From this point a known azimuth could be set to a nearby Trig Station, so true bearings were recorded. 

 

In this case the field crew were using older style equipment that required the vertical angle to be read and noted along with the slope distance, rather than the new fangled gadgets that automatically reduce the horizontal distance for you.

 

The data below has been tabulated from a field book

 

From Station 1 - Adopted Local Coordinates:

            East 2500

North 1555

RL 200

 

From Pt

To Pt

Bearing

Vert. Angle

Distance

1

2

16° 35’ 15”

93° 15’ 20”

134.828

2

3

83° 45’ 05”

88° 27’ 30”

103.127

3

4

67° 04’ 55”

86° 12’ 25”

101.051

4

5

111° 47’ 30”

92° 14’ 55”

158.772

5

6

191° 56’ 20”

93° 04’ 15”

77.511

6

7

142° 33’ 15”

90° 30’ 30”

95.174

7

8

241° 28’ 20”

87° 12’ 40”

106.076

8

9

276° 22’ 45”

88° 13’ 50”

151.522

9

10

306° 07’ 20”

90° 30’ 00”

95.150

10

1

274° 41’ 40”

89° 45’ 00”

102.825

 

 

 

 

 

 

Defining the Known Coordinates

You will see that the default Type of data on the first line is STN, which is exactly what we require, so press the Enter key to accept it.

 

Enter 1 for Stn number, and then the East coordinate of 2500, the North coordinate of 1555 and a height of 200. 

 

Now press the Enter key until you finish off the line and the cursor moves down to the next line.

 

The next line will also come up with a “STN” type of entry, but we only need the one station in this particular traverse, so we need another type of entry.

 

You can either allocate the individual entry types by selecting from the pull down list on each line, or, in the case where you will have a number of entries of the same type you can set a default entry type.

 

 

Entering the Traverse Legs

In this case, all the rest of our entries will be “Traverse” legs so you should set the default.

To do this, pull down the Options menu, and select the option “Default Entry Type”, as seen in the screen at left. From the list of the available types shown, select Traverse and then OK.

 

You will now see the Type change to Traverse, so press Enter to accept it.

 

If you look at the columns to the right you will see At Station (here it is 1), then To Point (here it is 2) .

Next you have Angle/Bearing which is 16° 35’ 15” followed by the Vertical Angles (93° 15’ 20”) and the Slope Distance (134.828).

 

For this example concrete pillars had been set up on each station at the same height, so the height of instrument and height of target were identical in all set-ups, with values of 1 being used for each.

 

Obviously in your real life work, you will need to enter in the values that you measure for both height of instrument and height of target if you are to obtain correct values for the heights of the stations.

 

Enter 1 for both height values, and press Enter to skip over the Point Code column, and you will see the cursor appears on the next line offering a default type of Traverse.

 

Press Enter to accept it, and then continue to enter the data shown in the table until you reach the end, to get a screen at right.
Define the Traverse Loop

Before you can go any further, it is necessary to define the route that your traverse took.

 

Now in this simple example, this step might seem a little redundant (and it probably is), but since this table can be used to enter large looped networks it is essential that you learn how to define the traverse loop.

 

To achieve this you need to enter a Fieldnote into the traverse table.

 

Bring your cursor up onto the line defining 1 to 2 and make sure it is in the “Type” Column.

 

Next Press the Insert Key on your keyboard, and you will see a new line is inserted into the table.

 

Pull down the options on this new line and select the “Fnote” type.

 

Press Enter to lock in the Fieldnote and the cursor will move to the next column.

 

The Fieldnote required to define the traverse loop is the letters “TR” followed by a space, and then a list of the points making up the traverse loop, separated by commas.

 

In this case the, points are from 1 to 10 inclusive, and then back to 1 to close.

 

The fieldnote would then be TR 1,2,3,4,5,6,7,8,9,10,1

 

Since this requires a far deal of typing, and, since it is common to have a traverse made up of a sequence of points, we have implemented a method of defining a sequence and minimizing the typing required.

 

Simply type the first point of the sequence, and full stop or decimal point, and the end point of the sequence, as seen in the alternative Fnote TR 1.10,1

 

So, regardless of how you decide to enter it, you need to enter it, and once you have done so you can now check on the misclose and accuracy of the traverse.

 

Calculate Misclose & Traverse Accuracy

You can either pull down the Option menu, and select Calculate Misclose, or, alternatively, select the button labelled “Re”  (short for ReCalc) shown at the left of the second line.

 

Either way the misclose, accuracy and perimeter should now appear in the relevant fields at the top of the screen as seen below.

 

Now, in this case you should achieve an accuracy of closure of 1:24147 that is well within acceptable limits.

 

Since you are within allowable limits, you may wish to adjust the traverse to form a perfect close, and if you so do, you can choose from the currently available adjustment methods of Bowditch, Compass, or Transit.

 

You may either pull down the Options menu, select Traverse adjustments, and then select your required method, or you can select the icons B,C, or T respectively.

 

Either way you choose to do it, it is important to remember that the adjustments are made to the coordinate values of each of the points, and NOT to the raw information that you have observed in the field and entered into the traverse table.

 

Once the adjustment has been made the program will advise you and inform you to use the Print to see the resulting adjusted values.

 

Calculate & Display Coordinates

 

The aim of the traverse exercise is to eventually produce coordinate values for the traverse points (and any side shots taken from them) and to store these points into the job database.

 

The first step in this process is to calculate the coordinates within the traverse sheet.

 

Pull down the Options Menu and select Calculate Coordinates.

 

Next, Pull down the Options menu again and select Show Coordinates (Or select the Icon with E+N on the toolbar).

 

Once the coordinates have been displayed you can use the scroll bar on the bottom of the screen to shift the screen view to the right and display the coordinate values as seen below.

 

In this case you will see that the coordinates at the end of the traverse match those given for the start indicating that we have achieved a closed traverse.

 

You should note that there is a small misclose of some 35 millimetres in the end height, and it is possible to adjust this out proportionally through the traverse stations if you wish.

 

 

Store Points To Database

 

Now that you have arrived at adjusted values for all the points, it is time to store them in the database.

 

Pull down the Options menu, and select Sore Points in Database. Then select all points and the points will be quickly stored.

 

You should now use File Exit to close down the traverse entry sheet, and save any changes.

 

You will see now that the points have appeared on the job screen as below.