def __init__(self, platform_id):
# check that the platform_id refers to a known satellite
if not Satellite.get_by_id(platform_id):
raise ValueError(
"platform_id does not exist: {}".format(platform_id))
self.platform_id = platform_id
self.segment_times = {} # segment_id : list of times
self.segment_positions = {} # segment_id : list of positions
self.segment_velocities = {} # segment_id : list of velocities
self.segments = Satellite.get_by_id(
platform_id).orbit_segments # Store orbit segments
def interpolate(self, timestamp, kind="linear"):
"""Estimate the position and velocity of the satellite at a given time.
Args:
timestamp: The time for which to get the estimated position and velocity, in Unix
epoch seconds.
kind: The type of interpolation to do. This defaults to "linear." Alternatives
include "quadratic", "cubic", etc. See scipy.interpolate.
Return:
A tuple (pos, vel). Each of pos, vel is a 3-tuple representing the vector
components of the position and velocity, respectively.
Raise:
ValueError if interpolation could not be performed for the given timestamp.
"""
# find the correct segment from stored data
segment = next(
(segment
for segment in self.segments if segment.start_time <= timestamp
and segment.end_time >= timestamp), None)
if not segment:
# segment was not in stored data, ask DB
segment = OrbitSegment.get_by_platform_and_time(
self.platform_id, timestamp)
if not segment:
raise InterpolationError("No segment found: {}, {}".format(
self.platform_id, timestamp))
else:
# update stored segments
self.segments = Satellite.get_by_id(
self.platform_id).orbit_segments
# get orbit records for the segment
segment_id = segment.segment_id
if segment_id not in self.segment_times:
records = OrbitRecord.get_by_segment(segment_id)
# don't bother to proceed if there are too few records for an interpolation
if not records or len(records) < 2:
raise InterpolationError(
"No orbit records found: {}, {}".format(
self.platform_id, segment_id))
# extract and cache time, position, velocity
self.segment_times[segment_id] = np.array(
[rec.time for rec in records])
self.segment_positions[segment_id] = np.array(
[np.array(rec.position) for rec in records])
self.segment_velocities[segment_id] = np.array(
[np.array(rec.velocity) for rec in records])
# interpolate the position and velocity
position = Interpolator.vector_interp(
self.segment_times[segment_id],
self.segment_positions[segment_id], [timestamp],
kind=kind)[0]
velocity = Interpolator.vector_interp(
self.segment_times[segment_id],
self.segment_velocities[segment_id], [timestamp],
kind=kind)[0]
return tuple(position), tuple(velocity)