如何将以地球为中心的惯性（ECI）坐标转换为以地球为中心的地球固定（ECEF）AstroPy？其他？ [英] How to convert Earth Centered Inertial (ECI) coordinates to Earth Centered Earth Fixed (ECEF) AstroPy? Other?

问题描述

我在卫星轨道的以地球为中心的惯性坐标（ECI）中具有位置（x，y，z）和速度（Vx，Vy，Vz）向量，最终希望以大地坐标（纬度，经度， & Altitude）。

I have position (x,y,z) and velocity (Vx,Vy,Vz) vectors in Earth Centered Inertial Coordinates (ECI) for a satellite orbit, and ultimately want to end up with geodetic coordinates (Latitude, Longitude, & Altitude).

根据此其他堆栈溢出问题，看来我需要转换为以地心固定地球（ECEF）坐标作为中间步骤（因此ECI-> ECEF- -> Lat / Lon / Alt）。

According to this other Stack Overflow question it seems that I need to convert to Earth Centered Earth Fixed (ECEF) coordinates as an intermediate step (so ECI --> ECEF --> Lat/Lon/Alt).

我知道ECI和ECEF共享相同的原点（地球质量中心），并且指向相同的z轴到北极。但是，我不确定将ECI转换为ECEF所需做哪些实际的方程式或调整。

I know ECI and ECEF share the same origin point (the center of mass of Earth) and the same z-axis that points to the North Pole. However, I am not sure what actual equations or adjustments I need to do to convert ECI to ECEF.

否则，如果有人知道Astropy或类似内容的任何固定转换那会更好。 （我还没有将ECI视为Astro Py或Space Py的选择）。

Otherwise, if anyone knows of any canned conversions on Astropy or something similar that would be even better. (I haven't seen ECI as an option on Astro Py or Space Py).

这是我用来生成轨道并获取位置和速度的代码向量。

Here is the code I am using to generate my orbit and get the position and velocity vectors.

from scipy.constants import kilo
import orbital
from orbital import earth, KeplerianElements, Maneuver, plot, utilities
from orbital.utilities import Position, Velocity  
import matplotlib.pyplot as plt
import numpy as np

orbitPineapple = KeplerianElements.with_period(5760, body=earth, 
e=0.05, i=(np.deg2rad(0)), arg_pe=(np.deg2rad(30)))
plot(orbitPineapple)
plt.show()
print(orbitPineapple.r)
print(orbitPineapple.v)

出：
Position（x = 5713846.540659178，y = 3298890.8383577876，z = 0.0）
Velocity（x = -3982.305479346745，y = 6897.555421488496，z = 0.0）

Out: Position(x=5713846.540659178, y=3298890.8383577876, z=0.0) Velocity(x=-3982.305479346745, y=6897.555421488496, z=0.0)

推荐答案

有许多不同的以地球为中心的惯性系，答案取决于您拥有哪一个

There are a number of different Earth Centered Inertial frames, and the answer depends on which one you have your coordinates in.

最常见的是所谓的J2000；它是根据2000年1月1日地球的方向定义的。另一种常见的方法是GCRF，它几乎相同（在80毫秒弧秒内）。

The most common is so-called J2000; which is defined w.r.t to the orientation of the Earth on Jan 1st 2000. Another common one is GCRF, which is almost the same (to within 80 milli arcseconds).

如果是这两者之一，则应该能够创建一个令人难以置信的 EarthLocation 对象并访问 lat ， lon 和 height 这样的属性

If it’s either of those two, you should be able to create an astropy EarthLocation object and access the lat, lon and height attributes like so

from astropy import coordinates as coord
from astropy import units as u
from astropy.time import Time
now = Time('2017-09-27 12:22:00')
# position of satellite in GCRS or J20000 ECI:
cartrep = coord.CartesianRepresentation(x=5713846.540659178, 
                                        y=3298890.8383577876,
                                        z=0., unit=u.m)
gcrs = coord.GCRS(cartrep, obstime=now)
itrs = gcrs.transform_to(coord.ITRS(obstime=now))
loc = coord.EarthLocation(*itrs.cartesian.cartrep )
print(loc.lat, loc.lon, loc.height)

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