He is most well known for his topographical survey of the Rhineland under Napoleon, and his assistance in measuring the meridian arc of France with astronomer Pierre Méchain to determine to length of the meter.
[3] Upon completion of this task, Tranchot studied astronomy with Pierre Méchain before he was given orders to triangulate and link his Corsica map with neighboring Sardinia and coastal Tuscany.
This task was completed with use of a new invention, the repeating circle,[4] from 1788 to 1791, and he was subsequently recognized by the Méchain and the French Academy of Sciences for his work.
[3] Following the cartography of these Mediterranean islands, Tranchot was approached by the French Academy of Sciences to accompany Méchain as his primary adjutant in measuring the southern part of meridian arc of France.
This project, spanning 1791 to 1799, started in Barcelona and ended at Rodez, and the resulting measurement became the basis for the metric system's unit of length, the meter.