MX Alignment - Writing Data Files [TN]

 Applies To 
 Product(s):Bentley MX Products
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 Original Author:Bentley Technical Support Group










This paper applies to the creation of Alignment data output files from the Interactive Alignment options within MX.



Prior to the creation of the Interactive Alignment options; Major options HALGN, HCUSP, VALGN, VERAT and VCUSP were used to generate design alignments. These were ASCII files that allowed geometry definition and when processed by MOSS (MX) they created Master and Geometry Strings.

With the evolution of interactive graphics there was a demand to be able to design alignments graphically and hence the creation of the Interactive Alignment option.

Since the creation of Interactive Alignment in 1990, users have been able to regenerate the alignments generated in Interactive Alignment by outputting an ASCII file from within Interactive Alignment. This creates a copy of the alignment in HALGN, VALGN and VERAT format to be used as a backup copy of their alignment.


How the files are written

The HALGN, VALGN and VERAT files analyze the completed alignment created in the Interactive Alignment option and then create a data file that 'best fits' the alignment by generating a fixed float, float, float scenario in the resulting data file.

Historically users have used these files as backup copies of their alignments so that they can create their entire design with a series of input files. Those users with experience of how the HALGN, VALGN and VERAT files are coded can also use them to make minor amendments to the geometry of the alignment and then re input the file to update the Master and Geometry string in MX.


Data Output accuracy

Because the data output files are a 'best fit' of the alignments generated in Interactive Alignment and they often cannot be stored to a sufficient accuracy in the data file, different iteration calculations can be made when the data output files are re-input into MX. This can lead to small discrepancies in the data between the original alignment and that generated by the data output files.



To create a true and accurate record of a master and geometry string created in Interactive Alignment users must make a GENIO file record of the alignment. This will store the alignment to double precision i.e. to 17 decimal places. 

To enable users to do this an option to generate a GENIO file at the data output stage in Interactive Alignment will be created at MX V2.5. This GENIO data file can subsequently be input into MX with other input files to recreate the entire design. If a user wants to amend a previously created alignment this must be done with the editing tools within Interactive Alignment to maintain alignment accuracy.

Depending on the length of the alignment and the point interval specified, the genio data for the master string may be very extensive, which in some working methods may prove to be inconvenient. To avoid this, store only only the data for the geometry string, but immediately following the data add an EDIT 029 command to regenerate the master string from the geometry string.

A more pragmatic approach - and still the most commonly used - is to generate the HALGN, HCUSP, VALGN, VERAT and VCUSP as required and run the input data file; then compare the resulting master and geometry strings with the original created in interactive alignment (either visually or using reporting tools) or simply check that the results are acceptable.  For the vast majority of cases this method proves entirely satisfactory, and provides the advantage that simple changes to the alignment (changing value of an intermediate free curve in VALGN or VERAT, for example) can be made by directly modifying the data, enabling extremely quick iteratation to optimize a design.  [Limitation: With this method is not suitable where interactive alignment has been used to store superelevation/cant points, as there is no linemode equivalent, and thus these points will be lost.  Use genio data instead]


See Also

Product TechNotes and FAQs

MX TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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