HOME  CDS Tutorial Manual
Form coordinates from section data
In this exercise you will learn how to
  • Enter and calculate the ‘frame’ points to define a road alignment
  • Define the string through those points.
  • Calculate coordinates of points entered from a level sheet.
  • Contour the co-ordinated points.
Why Do You Need to Learn This?
When points are picked up with a Level and tape, you bring back Chainage, Offset and Height which is all the values you need to draw Profiles and Sections.
However, since you do not have east or north coordinates, you cannot draw a plan, or contour the points.
Here we will show you how to calculate coordinates for this type of data, so that when all your electronic equipment is off on a major project, and your best client phones up with an urgent need to get out a contour plan of a small length of road, you will be able to dust off the automatic level and help her.
Before you can carry out these calculations, you must know the Alignment that these sections are meant to follow.
This is usually defined by a centreline, but can also be a control line offset from the centreline, as long as the offset is constant.
The drawing on top of the next page shows you the alignment of the data collected and used in Tutorial 5.
 
 
You should Start CDS and Open Job EX5 in the Foresoft\cds2\tutor folder.
Close the Job that was previously open, and Maximise the screen.
Do not be alarmed if the screen is blank, because if you remember from Tutorial 5, we had no coordinates, and without coordinates, the program has nothing to display on this screen.
Now the first thing to do is to enter the given coordinates of Point 1, which is the centreline point on our first section.
Add a Known Coordinate
Use the “?” key to bring up the Add/Edit/Query window, and Point 1 will be displayed as seen in the screen at right.If you look at its Chainage and Offset you should confirm that it has a chainage of 840 and an offset of 0, so it is the suspect we are looking for, so we need to give it the coordinates as seen on the plan.
Simply position the cursor in the East field and type in 17639.42.
Now Tab to the North field and type in 2746.079.
Now select OK.
You will be asked if you wish to save the changes, and you should select Yes.
Having established a coordinate for the starting point of the alignment we will now use the calculation routines to calculate the remaining points.
Calculate with Bearing and Distance
Pull down the Cogo menu and select Bearing and Distance
The from Point is 1 and the Bearing is 53.1736.
Enter the distance of 200, and then position the cursor in the field which says New Point.
From the alignment diagram, you see that the point on the centreline of the cross section at Chainage 1040 is point 33, so enter 33 for the new point.Select Apply, and a window will appear informing you that Point 33 is already in the database.
We are aware of that, and the function of this exercise is to give it some coordinates, which will in fact recalculate its position in terms of the plan view.
Select the radio button titled Recalculate, and then press OK.
You will see that the bearing and distance calc is ready to move on from point 33 which is fine.Position the cursor in the Bearing field where 53.1736 is still showing.
The bearing from the TP to the centre of a curve is at right angles to the straight, so press ‘R’ and you will see that the bearing has 90 added to it. 
Set the distance to 300, the new point number to 501 and select apply, and point 501 will be stored.
Now Cancel the Bearing and distance routine.
Arc & Chord Calcs
Pull down Cogo and highlight Curves, and then select Arc/Chord calculations.
The centre Point is 501, and the start point on the radius is 33
Leave “Absolute” and “Arc” selected and the clockwise button checked.
The Arc length is 120, and the new point is number 49.
When you apply this you will again be told that the point exists, so again select the Recalculate option.
Now Zoom Extents to get a view of the whole job.
Next you need to pull down Cogo, and select Bearing and Distance again.
From point is 49.
Position the cursor in the bearing field.
You are not shown expressly what the bearing you need is, but you have sufficient information to arrive at it as follows.
The bearing you need is at right angles to the line between Points 501 and 49.
 
Press the “P” key, click on point 501, followed by 49, and you will see the bearing between those two points appear. Press the “R” key and you will see the bearing alter by 90° to 76° 12’ 42”. 
Note, if you are not pointing to the points, you can type in 501,49 and then press the Tab or Enter key to get the original bearing. Then move the cursor back up into the Bearing field and press R.
The Distance is 80 and the new Point number is 61, and when you apply, you can again recalculate.
Next position your cursor in the bearing field, and this time press the “L” key to take 90 from the bearing shown. Enter a Distance of 250 and a Point Number of 502 and apply.
Next close bearing and distance, pull down Cogo and highlight Curves and select Arc/Chord.
The centre point is 502, the start point is 61, and you must make sure that the Anti-Clockwise button is selected. The Arc length is 160 and the new point is 85 which you will need to recalculate.
Next do another Bearing and Distance calculation from 85.
Use ‘P’ in the bearing field to specify the bearing between Points 85 and 502, and press ’R’’ to add 90 to this value. Enter a distance of 40 to a new point number of 90 which you will need to recalculate.
Now you have finished the calculation of all the alignment points it is time to define the alignment string.
Adding the Alignment String
Pull down the Strings Menu and select Add.
Pull down the folder field and select “lots” which is the only folder offered.
Enter an ID of “cl”, and then define the string s 1,33,+501,49,61,-502,85,90.
The screen will now be similar to that seen at right.Select OK and you have saved away the alignment.
Now select the Road option to open the Road window.
Pull down the Road menu, highlight Utilities and Select Calculate Coordinates from Chainage and Offset.
Calculate Coordinates from Chainage & Offset
The screen will now appear as below.
Pull down the Folder field and select ‘Lots” Now pull down the ID field, and select CL
Select All points to be calculated. Then select OK
Once the calculation is complete, you should see a screen similar to that shown on the below.
(If as sometimes happens, it doesn’t appear exactly like it is supposed to, don’t panic - simply do a Zoom Extents and all should be well.)
Form the Contours
Now, since we set out to prove that we could get a contour plan of points which you picked up with a dumpy level in cross section format, you should pull down the Contour menu and select Surface Parameters to see the screen below.
Since you have a couple of concave areas, it is wise to limit the maximum triangle side to prevent the formation of unwanted contours, so set a value of 90 metres.
Next form the model, and then calculate contours to achieve the screen above.