Thank you Sean for your answer No, my data have projected geographic coordinates. There are in NTF / lambert 2 étendue EPSG 27572.
Here is what I do in the script : I read a shapefile with ogr, I load them for using with shapely, I cut the lines every x meters and I save them in a new shapefile. The difference between the distance in input and the distance calculated by the software is very small. For exemple if I have 100km in input, the software calculate some distance about 100.130 km. It's insignificant, but perhaps the script's user might not understand. But if there no way to resolve that, I can specify this in the documentation. In any case the relief is not taken into account also, so it's not a big problem. Thank's
