Tutorial 22(a).

Interactive Horizontal Alignment Design.

Introduction

We are about to show an interactive horizontal alignment design. This is especially handy when trying to tie into existing designs; or when you don't have the coordinates of the new centre line but simply wish to design something by eye.

The Task

You have been given the topographic survey of the piece of land shown in CDS job 'roadtut1', and you are required to design a road through the property from the North West Corner to the South West corner. The job is in the my documents\cds2 directory and is installed with the program.

You have formed a model and calculated contours and the job appears as above.

How you go about determining where to place the road is up to you, and is not important within this tutorial

Be aware that you can use the Contour, Interpolate functions to extract preliminary 'what if' profiles quickly and easily through the various routes you might wish to trial.

What it basically comes down to is you need to apply your experience, and any local constraints which may apply to arrive at a horizontal alignment for the road.

In this case we will follow the ridge at top left – then cut across at a relatively constant height and follow the ridge bottom right to the end. We are first going to click in some points by eye and form a rough straight alignment. We will start these points at 10000 so that we can remember what they relate to.

From Points menu – click on “Add Points” and click in some points 10000 to 10003. Then from the strings menu we will string these points together. Click on strings – add and the string add dialog comes up. Put in a folder of “road” and an id of “cl”. For the string definition type in 10000.100004, (add in ' at end so that the string is drawn immediately) and you will have the rough alignment as shown below:

The string is selected in the above screen shot. Once selected the appropriate string grips are shown. We can move around the string if we wish. We will add in some arc's first and then do the fine tuning. The simplest way to add in some arcs is the “strings”- “utities” - “replace points with arcs”. We wish to replace points 10001 and 10002 with arc's. We first need to select these points. From the strings menu – select – select by range and select points in the range of 10001 ~ 10002. When running the menu item the program prompts for a value half of the maximum size that fit's. Except this value as a first try.

We have the following screen as shown above. We are now in a position to interactively move the alignment. At present we can move points that are not on an arc; we can move the IP of any arc or we can move in and out the center point to change the radius. To change the position left click in the box and while mouse is depressed move the grip. The string is redrawn as we go. The process is repeated until you are happy with the result. We have the screen as below:

Once we are happy we can unselect the string by pressing the escape key. If the screen needs to be redrawn single press the middle mouse button. At present spirals are not yet supported in the interactive string editting. For a design with spirals you will still need to use the Cogo – autoroad routines.