Road alignment formats

Road alignment reading

There are two ways to read horizontal alignmnet:

Real geometry:

Straight-arc-clothoid combinations are build with top points making tangents always continuous.
Problems are handled by reducing arc radiuses and clothoid parameters.
Usually very small reduction (maximum one percent) is enough.
Position and amount of correction is written to the log file.

GT-math:

Each element (straight, arc, clothoid) is handled separately.
Adjacent element tangents do not necessarily match.
Alignment remains exactly as in the original file.
Alignment cannot be edited with horizontal alignment edit function.

Method can be selected with converter settings GT-math checkbox. If the alignment is read using real geometry, program executes some checks:

Missing horizontal alignment section values are calculated automatically.
If two straight elements join without arc, warning "Zero radius corner" is given.
If there are zero length elements, warning "Zero length element" is given.
Offset measurement is calculated for all original alignment points and if they differ from zero, warning "Horizontal geometry error" is given.
Total length of the aligment is compared to the original alignment section values and if the length difference is more than 0.10 meters, warning "Horizontal geometry length error" is given.
Error message is given from orphan clothoids at the beginning or end of the file.
Error message is given from combination of three adjacent clothoids.

GT-math does not make any above mentioned checks and corrections. In both cases vertical alignment arcs are checked and if they do not fit, warning is writtent to the log file. Errors must be corrected manually with vertical alignment editing by reducing arc radius. This can be done easily with Maximum-button.

Found errors and warnings are displayed after conversion according normal settings. They can also be viewed with menu function File/Formats/Log File. Any remaining errors in the alignment are drawn using red color in both horizontal and vertical alignments.

Two joining straight sections without arc can be easily corrected by adding suitable radius in the horizontal alignment editing. All missing horizontal arcs can be added automatically by pressing Shift-Maximum. It asks the radius value and adds it to all zero radius corners. Suitable value is usually 0.1 - 1.0 m.