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Creating Legacy Alignments

This documentation describes the process of preparing legacy alignments. Legacy alignments are used by the Bureaus of Highway Design, Maintenance and Right-of-Way to determine where the existing roadway and structures are located, to better define our ROW assets.

Before You Begin

sample curve radiusBefore getting started on this process, it will be helpful to gather all necessary information from as-built plans of previous projects. For projects designed between 1987 and 1999, MX alignment data may already exist.

At each curve you will need to know the radius (R), deflection angle (Δ), and tangent distance between curves. Sometimes the curve data will show a degree of curve (Dc) instead of radius. In these instances, R = 5729.578 / Dc. If the alignment contains spiral curves, you will also need to know the length of spiral (Ls).

The legacy alignments can be created in either MX or MicroStation depending on the experience of the person creating them, the type of alignment, and available information defining the alignment. Ultimately, they need to exist in both forms. This documentation will describe both processes.

Regardless of the method chosen, there are some points to keep in mind.

  1. MX does not accommodate station equations in alignments. Equation locations must be identified and be generated as separate alignments.
  2. Although MX can be made to allow angle points in alignments, it is recommended that they be avoided. Separate alignments should be created wherever there are non-tangential connections.
  3. Alignments containing spiral curves need to be created in MX.
  4. Bearings on older plans are based on magnetic north. Alignments created using those bearings will need to be rotated to match the present grid system. This may be easier to accomplish after all alignments for the project have been created.

Creating the Alignment in MX

Attempting to describe methods for creating alignments in MX is a topic too large for this document. If you have experience with MX's alignment options, you may find this to be a good method for recreating the legacy alignments.

This process is best suited for projects where you have PI coordinate information. If that is the case, it is relatively easy to create a series of tangent lines using the PI coordinates and insert the curves based on the as-built plan curve data. MX should be used for generating alignments containing spiral curves.

The alignment options are not available if the display is empty. You must start by drawing the survey detail or other strings that may be available. If the project does not have any existing detail or other strings in the project area, at least one string must be created or consider using MicroStation for creating alignments. This can be done with the Create a String option under Modify > Edit Strings. Enter coordinates in the project area for string points. This could be used to create a feature string representing a segment of the alignment to be generated.

The exact process used will be dependant on what alignment information is available. If you need help with the Alignment options, please see your CAD/D Coach or Jerry Gall for assistance.

Use the Alignment option on the Design menu and create model called Legacy. Remember to check model defaults. They should be set to use the mxroad style and feature sets. Select the Horizontal Design option.

If the project contains alignments with spiral curves, there is a setting that should be checked. Before entering the alignment name, check the Design Parameters. This will open the panel shown below. Make sure that the Spiral Formula is set to Clothoid.

element design parameters dialog box

Specify the new alignment string label. Legacy alignments use the MC_L naming convention. There are multiple options here. The two most common would be:

  1. If you have coordinates for the PI points, create alignment segments selecting the Fixed Horizontal option followed by the Two Points method. Enter pairs of coordinates for each tangent section and then use the Free Curve method Radius option to insert the curves. Don't forget to include any spiral data.
  2. If coordinate data is not available from other sources, the start and end points of the first segment can be selected from MicroStation's basemap drawing (all.dgn with Live Nesting set to 1). For subsequent segments, use the Two Points method selecting the intersecting point from the prior segment and then use the Angle & Distance Construction method for the other point. The dialog box for this option is shown below.
single construct dialog box

Point 1 - the point where the constructed point will be defined from.
Point 2 - the point defining the direction where the angle will be measured from.
Angle - the deflection angle of the curve (Δ) with spaces separating degrees, minutes, and seconds. Angles turning towards the left will be negative.
Distance - the negative (-) value of the length of the segment or the distance between the PIs. Note that this is not the difference between stations of two consecutive PI points. It is the sum of the tangent length of each curve plus the distance between the PT of the first curve and PC of the next curve.

Creating the Alignment in MicroStation

smartline command dialog boxThe more familiar you are with the SmartLine command and AccuDraw, the easier this process will be. You may find it easier to enter the alignment data if AccuDraw is set to polar mode. If AccuDraw is showing rectangular coordinates (XY), it can be toggled to polar (Distance/Angle) by hitting the Spacebar key while AccuDraw is active. This process is NOT for alignments containing spiral curves. Please create these in MX.

Drawing the alignment will be easier if you know the length of each tangent section along with the radius and deflection angle of each curve before starting. Having detail in the background as a reference will simplify the process and make it easier to locate any mistakes made along the way. If the project does not have any detail, attach aerial photos or the state basemap as a minimum.

reverse curves buttonDepending on the available information, it may be easier to draft the alignment backwards and reverse it after. This is done by using the Change Element Direction tool. This tool can be found on the Modify Curves menu (Tools > B-spline Curves > Modify Curves).

To start, rotate the view along the first segment of the alignment. Other angles will be defined from this point based on curve data. If you do not have coordinate information for the start point of the first alignment, it may be necessary to select a point based on aerial or basemap information.

  1. Select the first point of the alignment.
  2. Move the mouse in the desired direction and type the length of the first tangent section (first point to first PC) into AccuDraw's Distance box.
  3. Place the second point. The AccuDraw compass will rotate to the direction of the line just drawn.
  4. Change the SmartLine Segment Type from Lines to Arcs. SmartLine is now expecting you to locate the center of the arc.
  5. Move the mouse to the right or left of the line depending on the direction of the curve. Enter the curve radius in AccuDraw's Distance box.
  6. With the Angle at 90° or -90°, locate the next point.
  7. If AccuDraw is set to polar mode, note how the angle changes as you move the mouse to define the arc. Enter the deflection angle in AccuDraw's Angle box. Note that the ˆ is used instead of the ° symbol when typing the values and there are no spaces between the degree, minute, and second values.
  8. Toggle the SmartLine Segment Type from Arcs back to Lines if the next segment is a tangent and draw the next segment.

Transfer Alignment to MX

If the alignment was drafted in MicroStation, follow the steps outlined in Transferring MicroStation Alignments to MX to create the alignment in MX.

The transfer process does not name the alignments properly. Use the RenameM add-in to rename the new alignment to conform to the MC_L naming convention.

Transfer to MicroStation

Draw the alignments in MX using the NHAlign add-in and transfer to MicroStation. This will create a new MicroStation drawing with the alignments created according to Department standards.

New Hampshire Department of Transportation
PO Box 483  |  7 Hazen Drive  |  
Concord, NH  |  03302-0483
Tel: 603.271.3734  |  Fax: 603.271.3914