Horizontal and Vertical Alignment QA

Check the Horizontal and Vertical Alignment using the Alignment Editor in TBC. You can also run the Alignment Geometry Report to give you a PDF or paper copy to work with.

Checking a Horizontal Alignment

  1. Check the Start and End Coordinates for differences to the plans
  2. Check the start and end stations / chainage of the alignment
  3. Check the Station Equations applied to the alignment
  4. Check the alignment for deflections (use CTRL and Click on the Settings Icon - deflections will be displayed in the alignment editor)

If you find any discrepancies in the above, you should check each geometry element (Straight, Arc, Spiral) start and end station, start and end coordinate and geometrical properties like radius or spiral type and spiral length.

It is also helpful if you have the PDF Plan Sheets Georeferenced into the project to do a visual inspection that your alignment matches its location on the plans - this can pick up some errors also that should be picked up also by the data.

Commonly Encountered Problems - Horizontal Alignment

  1. Sometimes the geometry of a HAL is provided in PI form and sometimes in geometrical element form. Often a geometrical form of data is written only to 2 or 3 decimal places, which is sometimes insufficient accuracy to recreate the alignment correctly, and will introduce discrepancies.

  2. Sometimes the geometry of the alignment will have small deflection angles at the element changes to accommodate a design requirement. Sometimes these are deliberate, sometimes they are a factor of the output to e.g. LandXML format and can create problems unnecessarily. If your alignment has a deflection angle in it, you cannot use the Alignment Based Surface Modeling approach because that depends on truly curvilinear alignments.

  3. Sometimes the alignment will have very short segments (0.001m / 0.005’) or less and sometimes even elements that reverse the direction of the alignment for a very short distance. these will create some problems

  4. Typically you will find Clothoid Spirals on highways projects. On Rail projects however you can find a range of different spiral types. You need to make sure that you know the type of spiral and set the correct property on the alignment for the geometry to compute correctly. Railways use BLOSS, Railway Spiral, Cubic Parabola, Half Sine etc type spirals and all have slightly different computation algorithms)