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Handle polar positions in height calculation #842

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Handle polar positions in height calculation #842

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19 changes: 16 additions & 3 deletions skyfield/toposlib.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
# -*- coding: utf-8 -*-

from numpy import arctan2, array, array2string, cos, exp, sin, sqrt
from numpy import (
arctan2, array, array2string, asarray, cos, exp, float64, sin, sqrt
)

from .constants import ANGVEL, DAY_S, RAD2DEG, T0, pi, tau
from .earthlib import refract
from .framelib import itrs
Expand Down Expand Up @@ -143,6 +146,7 @@ def __init__(self, name, radius_m, inverse_flattening):
self._one_minus_flattening_squared = omf * omf
f = 1.0 / inverse_flattening
self._e2 = 2.0*f - f*f
self.semi_minor_axis = Distance(m=radius_m * (1.0 - f))

def latlon(self, latitude_degrees, longitude_degrees, elevation_m=0.0,
cls=GeographicPosition):
Expand Down Expand Up @@ -210,9 +214,18 @@ def height_of(self, position):

"""
xyz_au, x, y, aC, R, lat = self._compute_latitude(position)
height_au = R / cos(lat) - aC
height_au = self._compute_height(R, lat, aC, xyz_au)
return Distance(height_au)

def _compute_height(self, R, lat, aC, xyz_au):
height_au = asarray(R)
near_pole = height_au <= 1.e-12
if near_pole.any():
height_au[near_pole] = abs(xyz_au[2]) - self.semi_minor_axis.au
else:
height_au[~near_pole] = R / cos(lat) - aC
return float64(height_au)

def geographic_position_of(self, position):
"""Return the `GeographicPosition` of a ``position``.

Expand All @@ -224,7 +237,7 @@ def geographic_position_of(self, position):
"""
xyz_au, x, y, aC, R, lat = self._compute_latitude(position)
lon = (arctan2(y, x) - pi) % tau - pi
height_au = R / cos(lat) - aC
height_au = self._compute_height(R, lat, aC, xyz_au)
return GeographicPosition(
latitude=Angle(radians=lat),
longitude=Angle(radians=lon),
Expand Down