We suggest you give the two previous tutorials to gain some background into the method of least squares grading. We assume that you know how to collect the raw data necessary.
In this example we wish to tile the supplied surface into a number of separate fields to minimize cut and fill etc. The design consists of 3 stages. In first stage we need to decide on the number, size and placement of the individual fields. In second stage we get the software to calculate the best fit plane's for each separate field. We may need to go back to stage 1 here and tweak the horizontal layout if necessary. The third stage consists of reports etc needed to construct our design.
The horizontal layout consists of first deciding on field sizes and setting out our design so that each field most closely represents the natural surface. The best layout is a combination of experience and planning. We need this section right to optimise our design. In a fact finding mission to Bali we discovered that the steeper the slope the thinner the individual fields need to be made in order to minimize the amount of cut and fill etc. Conversely the flatter the surface the larger the individual fields can be.
CDS has a number of tools which can help in the initial planning. The first step is to triangulate and contour the area. From the contours we can estimate the initial design. Another helpful tool is the instantaneous height display on bottom right of the screen. If we have a triangulated surface CDS reports E,N and height at the bottom right of the screen. This helps us guestimate the cut and fill depths before starting. Another help is the 3D view option which allows for a vertical exaggeration to enable us to sight any ridges, valleys etc.
We are now going to work through an example on how we would go about doing this: From ftp://ftp.foresoft.com please download the cab file grading3.cab Open up CDS go to options and then "restore" menu item. You can now open the grading3 database. After triangulating and contouring (if you are not sure on how to do this please refer to tutorial ### ) ; we can display the following.
 |
This job slopes from the right of the screen to the left.
From the "J" Join command we know that the grade is
approximately 1.5% . ie Type in j and select a point bottom right of the
screen and then a second point at top left. The join dialog reports a
slope of about 1.5%.
Also on picture we have lined in two points of interest. Position 1 shows position of a gulley extending half way down the slope. |
Position 2 is a slight ridge line. Our design brief is to design some fields with a run-off in any direction of 0.5% and to have a maximum cut and fill value no greater than a meter. We also wish to minimize the total cut and fill and also wish that the cut and fill balances. We also notice that the maximum height is 45 and the minimum height is 41.
As the contours are reasonably uniform we have decided on laying the fields across the slope with a retaining wall between fields. Next step is to decide on the number of fields. Our Balinese farmer could conceivably layout the fields using the contours shown to give about 20 distinct fields. As we have access to heavy machinery we will be using larger fields. In our initial design we will use 4 fields. This should give us a maximum cut or fill of about 0.5 meters on any single field. The existing contours are a reasonable guide to laying out the field. ie each field should contain the same number of contour intervals as a rough guide; and the edge of the field should roughly follow the contour line if we are working towards minimising the cut and fill values for the job.
Our initial design follows:
We have split the fields into roughly 4 equal area fields. Also each field should slope slightly from top of the screen to the bottom as well as down the slope. Also note that each field has been designed with a one meter gap between fields. This allows for a bank etc between each field. It is also necessary to avoid potential problems were a single point lies on the boundary of two adjacent fields and would have different heights depending on field it was placed - ie a singularity in mathematics.
When creating the design contours later we wish to avoid the situation were any created triangles are formed across the embankment. The embankment edges are discons/breaklines. We will also create some extra points along these bank edges rather than create long skinny triangles which would be the case if we only have two or three points in the break-line.
In our example the edge of field1 consists of the points 70000,70001 and 70002. We wish to create some extra points between them and enter it as a breakline. From the "Cogo" menu select "Road Calcs" and "Equal segments". In this example we have created a new series of points from 80000 upwards. Do this for each bank edge and string them together. Add them to the folder "discon2"..
Important For these points to be included in the grading calculations then they must have been included in the original base surface triangulation. From contour menu select surface parameters - surface point selection and reset the point range so that all the points are included.
We have done a preliminary horizontal design of our field layout. We can now design the vertical grading for our fields. CDS grading option has been designed so that we can grade each field independently. From the "Grading" menu select the "Random Point Grading" option. The following dialog is presented:
 |
The first time in the Field number defaults to 1. We will
use number 1 to represent field 1. We also need to fill in the Bounding
String which is the closed string representing the field outline. Here our
bounding string is in folder fields with an id of 1. Fill out any other
fields as necessary and press the Apply button.
Click on the Land Grading tab at the top of the screen. We are now presented with the following dialog. |
| Again fill out any box's as appropriate. In this case we
have left the cut / fill ratio at 100% but this does vary.
With the axis bearings we suggest that you first run grading with default bearings. Once done from the reports you can obtain the bearing of max cross- fall. In this case it was about 312 degrees which is close enough. Click on the "Calc Grades" to run the least squares grading. The grades along axis1 and axis2 are reported. |
 |
You will see that the grade reported is larger than the max allowable for this example of 0.5%. To limit the grade click in the "Adjust Grades" tick box and fill in the new value or values in appropriate edit box. We now rerun the "Calc Grades" to limit the max grades.
We can now triangulate and contour the first field to check our design. To create design surface click on the "contour" menu and surface parameters. Create a new surface and call it design. Triangulate and contour. The design contours should be equidistant.
Field 2 has been defined in the horizontal by the string in folder fields with string id of 2. Click on the "random grading" button. Click on the add button at the top of the dialog and define a new field number 2. Fill in the bounding rectangle and when happy click the apply button. As before we can now calculate the new grading surface.
Repeat the procedure for fields 3 and 4.
We now have our finished design; as seen below.
For a graphical view of cut fill distribution we suggest that you create a new contour surface. Call it a difference surface so that we are contouring the difference between the design and natural surface. Turn on surface shading and display as below. This gives us a graphical view which can help us refine our design. This may entail going back to the horizontal layout and performing the process iteratively until we are happy with the result.
In our example here we can see that we are dragging dirt from top left of each field to top right. We could minimize the dirt movement by rotating all the fields counter-clock wise to minimize the haulage distance.
Please see the previous tutorial on report generation. At present CDS can only generate a per-field report.