Math domain error when computing elevation in certain corner cases

[astrojuanlu]

We encountered a case of a target that was precisely under the orbit of the satellite and because of rounding errors the argument of the arc sine was greater than 1:

ValueError: math domain error
[...]
  File "orbit_predictor/accuratepredictor.py", line 180, in __iter__
    pass_ = self._refine_pass(ascending_date, descending_date)
  File "orbit_predictor/accuratepredictor.py", line 234, in _refine_pass
    tca = self._find_tca(ascending_date, descending_date)
  File "orbit_predictor/accuratepredictor.py", line 248, in _find_tca
    if self.is_ascending(midpoint):
  File "orbit_predictor/accuratepredictor.py", line 274, in is_ascending
    next_elevation = self._elevation_at(when_utc + ONE_SECOND)
  File "orbit_predictor/accuratepredictor.py", line 265, in _elevation_at
    return self.location.elevation_for(position)
  File "orbit_predictor/locations.py", line 78, in elevation_for
    return asin(top_z / range_sat)

with top_z = 509.4044680189018 and range_sat = 509.40446801890175. There should be something in the code that prevents this, like

    return asin(min(top_z / range_sat, 1.0))

[astrojuanlu]

Happening again.

    109         range_sat = sqrt((rx * rx) + (ry * ry) + (rz * rz))
    110 
--> 111         return asin(top_z / range_sat)
    112 
    113     def get_azimuth_elev(self, position):

ipdb> p top_z
489.56483852668225
ipdb> p range_sat
489.5648385266822
ipdb> p top_z / range_sat
1.0000000000000002