code: def euler(
      lat1,
      lon1,
      lat2,
      lon2,
      ell: Ellipsoid = None,
      deg: bool = True,
  ):
      """computes the Euler radii of curvature at the midpoint of the
       great circle arc defined by the endpoints (lat1,lon1) and (lat2,lon2)
  
      Parameters
      ----------
      lat1, lat2 : float
          geodetic latitudes (degrees)
      lon1, lon2 : float
         geodetic longitudes (degrees)
      ell : Ellipsoid, optional
            reference ellipsoid
      deg : bool, optional
            degrees input/output  (False: radians in/out)
  
      Returns
      -------
      radius: float
          radius of sphere
      """
      if not deg:
          lat1, lon1, lat2, lon2 = (
              degrees(lat1),
              degrees(lon1),
              degrees(lat2),
              degrees(lon2),
          )
  
      try:
          lat1, lat2 = asarray(lat1), asarray(lat2)
      except NameError:
          pass
  
      latmid = lat1 + (lat2 - lat1) / 2  # compute the midpoint
  
      # compute azimuth
      az = vdist(lat1, lon1, lat2, lon2, ell=ell)[1]
  
      #   compute meridional and transverse radii of curvature
      rho = rcurve.meridian(latmid, ell, deg=True)
      nu = rcurve.transverse(latmid, ell, deg=True)
  
      az = radians(az)
      den = rho * sin(az) ** 2 + nu * cos(az) ** 2
  
      #  compute radius of the arc from point 1 to point 2
      return rho * nu / den
  
file_path: pymap3d/src/pymap3d/rsphere.py
imports: from __future__ import annotations
  from .None import rcurve
  from .ellipsoid import Ellipsoid
  from .mathfun import cos, degrees, log, radians, sin, sqrt
  from .vincenty import vdist
label_desc: Use image node_id 4 for calling a global function with example usage: euler(lat1, lon1, lat2, lon2, ell, deg) and returns: unknown