The +init= syntax is deprecated. So all you need is the ESRI:102001 part. See: https://pyproj4.github.io/pyproj/stable/gotchas.html#init-auth-auth-code-should-be-replaced-with-auth-auth-code
inputGDF.crs = 'esri:102001'
First, let's see what the mapping between a Y-X plane and a Lon-Lat plane would look like:
Y-X-H coordinates are Cartesian ones.
Since you named it Gaussian coordinates, it is suposed to Y and X are Transverse Mercator projections of the geodetic coordinates.
I am assuming that Y coordinates are Eastings and X coordinates are Northings. ...
You need to set the environment variables to run the QGIS python outside.
In this case my QGIS installation is in D:\QGIS, so you should only change OSGEO4W_ROOT.
The issue you are having is due to axis order changes in PROJ 6+: https://pyproj4.github.io/pyproj/stable/gotchas.html#axis-order-changes-in-proj-6
One solution is to use always_xy:
from shapely.geometry import LineString
from shapely.ops import transform
from functools import partial
roadsegment = LineString([(5.318945751388698, 50....
@jelleve, your answer is correct and in line with https://pyproj4.github.io/pyproj/stable/advanced_examples.html#optimize-transformations.
Additionally, you may be interested in geopandas. It will enable you to read/write these geometries and reproject them using the same method you showed above using one line of code:
gdf = geopandas.read_file("input....