# Questions tagged [coordinates]

Questions about sets of data used to determine a unique point in a given space, e.g. (degrees North, degrees East) for geographic coordinates

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### Better way to get approximate ground track for a satellite using Skyfield?

I wanted to make a quick ground-track plot, so I used the Python package Skyfield to propagate a TLE and return Earth-Centered Inertial coordinates. Then I created a ...
679 views

### Is this commonly attributed ECI (Earth-Centered Inertial) to ECEF (Earth-Centered Earth-Fixed) transformation accurate?

As noted in this previous Stack Exchange question, and many others like it, the transformation from ECI to ECEF (or vice versa) is not a simple process, requiring several steps and considerations (...
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### ECI to LVLH conversion

I want to transform the position and velocity of two satellites from ECI mean of date mean of equinox to LVLH(Local Vertical Local Horizontal). The problem is that there is little documentation that I ...
464 views

### Shape and dimensions of the Moon's reference surface for selenographic latitude/longitude?

For Earth, the reference surface for "GPS" latitude, longitude, and altitude is the WGS84 ellipsoid, with equatorial and polar radii $a, b$ of 6378.1370 and 6356.7523 kilometers, respectively. ...
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### Transform ECI to ECEF

I need to transform ECI to ECEF coordinate. Here, I need the formula in math and algorithm. I have looking for the formula in the internet, but I can find one. I have x, y, z cartesian coord in ECI. ...
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### C/Fortran library for ECI to ECEF conversion

Does anyone know of a good C or fortran library which constructs the rotation matrix to convert from ECI to ECEF components?
148 views

### Will these equations give me the approximate apparent RA and Dec using positions from Horizons?

In this answer @DavidHammen showed me how to get coordinates from JPL's Horizons using the Earth's equatorial plane as a reference plane by selecting ...
286 views

### How were the geodetic and geocentric latitudes of the Space Shuttle defined and calculated?

The image below is cropped from https://i.stack.imgur.com/4XFaJ.jpg as described in this answer. It shows a geographic state of a space shuttle at a given instant in time. There is only one value for ...
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### Coord. system:collection of charts (local homeomorphisms to ℝ𝑛) for differentiable manifold 𝑀, frame:section of tangent vector fiber bundle over 𝑀

This answer to Are ECI and ECEF both frames and/or coordinate systems? Is there a difference? (which asks about the difference between coordinate systems and frames) says: In the language of pure ...
336 views

### Why was this point chosen as the origin for the Saturn V coordinate system?

David Hammen gently corrected my erroneous comment on this fine answer to the question: How is the height of a rocket measured? by pointing out the following figure in the Project Apollo Coordinate ...
415 views

### How can Earth-Centered Inertial (ECI) coordinates be properly called "inertial" if the Earth's orbit is always accelerating towards the Sun?

I've just realized (again) that I don't understand anything, something that often happens to me after reading a @DavidHammen answer. How can Earth-Centered Inertial (ECI) coordinates be inertial if ...
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### How to convert body coordinate from Sun reference frame to Earth reference frame?

I have the coordinates of a celestial body w.r.t. Sun , expressed as (x,y,z), at a given time. I need to move this coordinates into a reference frame centered on Earth center, but after reading dozens ...
407 views

### Are any spacecraft heading remotely where Planet 9 is expected to be?

Planet 9, the hypothetical planet predicted Batygin and Brown, is expected to have an apoasis near the galactic center. Is there a spacecraft that is heading in that direction? Specifically, they ...
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### Accuracy of ECI (J2000) to ECEF (WGS84) for a LEO satellite only accounting for Earth Rotation

I am working on developing a simple J2 orbit propagator for a project I am working on and am at the stages of converting from ECI to ECEF. Looking at this reference document in section 2.4, what ...
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### What are the problems that need to be taken in consideration when trying to find planetary position by using jpl ephemerides?

I'm currently trying to determine the position of the sun and the moon from jpl ephemeris DE200 which is referred to the dynamical equator and equinox of 2000 and uses tdb time. I am using the j2000 ...
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### How do I find my coordinates using x, y and z variables and trilateration?

For a school project, I was really interested in finding my own location using information from satellites, by using trilateration (so basically do what GPS are doing but by myself and with some math)....