The Alignment Creation Tools are housed within Civil 3D’s version of a toolbar and consist of a comprehensive set of commands to create and edit the lines, curves, and spirals that make up an alignment.
To create an alignment using the Alignment Creation Tools, follow these steps:
- Open the drawing named Alignment Creation Tools.dwg located in the Chapter 05 class data folder.
- Examine the blue geometry and accompanying dimensions and notes.
This geometry is described in detail in the sidebar “Using Temporary Geometry.” - On the Home tab, click AlignmentAlignment Creation Tools.
- In the Create Alignment – Layout dialog box, click OK to accept the defaults.
- On the Alignment Creation Tools toolbar, click the black triangle on the first button on the left to expand it downward (see Figure 5.3). Then click Tangent-Tangent (With Curves).
Figure 5.3 Selecting the Tangent-Tangent (With Curves) command. - Snap to the center of the circle marked A.
- Snap to the centers of circles B through E and press Enter. The Jordan Court alignment is created.
- To create the Madison Lane alignment, repeat steps 3 through 7 entering Madison Lane for Name and using circles F through H.
- To create the Logan Court alignment, repeat steps 3 through 7 entering Logan Court for Name and drawing it from circle I perpendicular to the Madison Lane alignment.
Alignment Terminology
Before jumping into the next exercise, you may want to review the following list of terms that you will find throughout the Alignment Creation Tools commands as well as other places within Civil 3D:
- Tangents (alignment segments)
- The straight-line portions of an alignment
- Tangent (geometric condition)
- Touching or passing through at a single point
- In the case of a line and arc: perpendicular to a line drawn from the intersection point to the center point of the arc
- In the case of two arcs: intersecting in such a way that a line drawn from the center point of one arc to the center point of the other arc passes through the intersection point
- Curves
- The curved portions of an alignment that have a constant radius.
- Spiral
- The curved portions of an alignment that change in radius from one end to the other
- PI (point of intersection)
- The place where two tangents intersect or would intersect if they were extended
- PC (point of curvature)
- The place where the curve begins
- PT (point of tangency)
- The place where the curve ends
- Free
- A line, curve, or spiral that is dependent on another alignment segment at both ends
- Floating
- A line, curve, or spiral that is dependent on another alignment segment at one end
- Fixed
- A line, curve, or spiral that is not dependent on another alignment component at either end
Using Temporary Geometry
Existing physical and legal boundary features almost always influence the layout of any land development design. In a residential project such as the example in this book, the goal is to create as many optimally sized lots as possible within the available area. Every lot must also be accessible from roads built through the site. With these things in mind, along with the geometry of the existing property boundaries, terrain, and other constraints, it is often helpful to create some temporary geometry to guide you in the creation of the alignments.
In the drawing for this exercise, the blue linework is provided for you and represents reference geometry to existing features of the site. Dimensions and notes have also been provided to help explain the reasoning behind this geometry. The following list represents key considerations when creating this temporary geometry:In the real world, you will need to come up with this temporary geometry on your own. In fact, this is what design is really all about: using your knowledge and creativity to come up with a technical solution to a need or problem. Creating the alignment is the easy part. Coming up with the temporary geometry as described here is the real challenge.
- 150' (45m) offset from road centerline to back of lots to accommodate 50' (15m) right-of-way, adequate front yard, single-family residence, and adequate rear yard
- Perpendicular intersection with existing road that is ideal for safety and accessibility
- Avoidance of steep area to the south
- Uniform geometric properties where possible, such as 90-degree angles, parallel lines, and so on. This is recommended for simpler, more efficient stake-out and construction
- Avoidance of the farmhouse and buildings, because that part of the property will be deeded back to the original owner