A field measurement of any kind is never exact and intrinsically contains errors (NJDoT Survey Manual – 2014). For track topographical measurements some of these errors are known and eliminated by applying appropriate corrections and compensations. Even after all known errors are eliminated however, a site measurement will still be in error by some unknown value. To minimise the effect of errors, the surveyor has to make carefully the measurements and to use only appropriate and well calibrated equipment.
As any kind of field measurement, the track versine surveying is subjected to different types of errors which are affecting the survey precision. Most of them are easily overcome by following the measurement procedure and using the correct equipment – which is basically a chord and a graduated ruler (both fixed or not on special design pads).
The result of the survey is a set of measured versines. As part of the quality assurance process, the versine (Hallade) survey is deemed sufficiently precise and not significantly affected by random errors, if the measured versines satisfy this formula (Radu – 2003):
– Σvodd is the sum of the versines measured in mm at odd points
– Σveven is the sum of the versines measured in mm at even points
– n is the number of survey points
This formula is derived from the standard error of the mean and is based on the theory of measurements and errors.
Theoretically the sums should be equal as they are related to the deflection angle measured between the curve tangents.
- Radu, C. (2003) Rectificarea si retrasarea curbelor de cale ferata (Rectification and realignment of the railway track curves). Course notes. Technical University of Civil Engineering Bucharest.
- NJDoT (2014) Survey Manual. New Jersey Department of Transport. (available online: http://www.state.nj.us/transportation/eng/documents/survey/)