# 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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### How is the Celestial Ephemeris Pole (CEP) exactly defined?

I am currently trying to understand the definition of the True Equator Mean Equinox (TEME) frame. I found a very nice explanation in @NgPh's answer to Can someone explain to me the TEME reference ...
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### How to calculate velocity vector in perifocal coordinates [closed]

Well the formula for it is here: Though if r is the radius and f is the true anomaly (which I assume is radians), then what is r dot and f dot 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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### Do geodesics close on an ellipsoid?

I want to calculate the shortest distance between two points (Point A and Point B) on the ellipsoid surface. For this I need to use geodetic passing through these two points. Well, if I continue this ...
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### Translate/shift ECEF coordinates given certain distance

I have some orbits in ECEF coordinates overlapped at the origin, and I would like to "move" some of them given a certain distance from the original orbit similar to the following picture: ...
112 views

### How to convert to GEO cordinate from the Mars Solar orbital coordinate (Sun-state)

I am working on the planetary science (on Mars) project for my master thesis. I am using MAVEN data for analysis. Data (spacecraft position) are measured in MSO (Mars Solar orbital) coordinate. I ...
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### Coordinate systems for state vectors

I am currently working on a project from this book. In appendix D, they provide a few projects that can be coded as a review of all the material in the book. I finished the first project, Site/Track ...
158 views

### 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)....
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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 ...
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### 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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### Can't find ISS position data API that uses the https protocol

I have used the open-notify API to track the ISS in a script I've written. It's just excellent, but it doesn't use the secure version of the http protocol. Now I find myself trying to include it on my ...
115 views

### 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 ...
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### When B is directly below A, as shown, what's B’s velocity (in vector notation) relative to A?

Spacecraft A and B are in coplanar circular orbits around the Earth. The orbital radii are as shown in the figure. (Not looking to use C-W equation. Just the equation describing relative velocity ...
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### CesiumJS: how to convert Alt/Az as seen from Earth surface in (x,y,z) position w.r.t Earth center?

I know how an antenna located on Earth surface is poiting to an object in space, by means of Altitude and Azimuth. I would like to show the pointed object in the 3d view, so, as far as I can ...
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### Should coordinate transformations from J2000 to ITRF93 in quaternions be cyclic?

I used SPICE's pxform at an interval of epochs to determine the transformation from J2000 (inertial) to ITRF93 (Earth body-fixed) frame. Then, I converted these rotation matrices to quaternions with ...
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### Which are the correct input parameters for NASA Horizons query to get the right Alt/Az data needed to plot analemmas for various planets?

I tried to replicate these analemmas, taken from a discussion of the equation of time in the following post: http://pbarbier.com/eqtime/eqtime.html: I used "Quantity n.4" for Nasa Horizons ...
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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?
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### Could the orbit of a satellite place it on the z-axis of the ECI coordinate frame (x=y=0)?

It is mostly a hypothetical question; I assume the answer is no, but I am looking for any data to contradict my claim that there are none or at most only one satellite at a time which could ever ...
390 views

### Accuracy of direct ECI (Earth-Centered Inertial) to LLA (Longitude, Latitude, Altitude) conversion via sub-satellite point?

The process of converting between ECI and LLA is generally known to be complex, as it involves a intermediate conversion to ECEF (Earth-Centered, Earth-Fixed). This, in turn, involves the ...
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### Orbit Elliptical Fitting

Question: Given a set of XYZ (3D) coordinates in the Earth-fixed frame, after converting them to the inertial frame, how do I perform orbit fitting in the least-squares sense (meaning minimising all ...
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### A spacecraft is travelling at X units per hour. But relative to what exactly? Does it depend on orbit? How?

If I am walking, the ground is stationary, and I move X units/hour relative to the ground. If I am in low-earth orbit, then I am still moving X units/hour relative to the ground, only its a much ...
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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 ...
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### 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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### Longitude deadband of geostasionary satellite

I try to count longitude deadband of geostationary satellite (0.1 degree). But I still confused, where should the longitude I have to start? In the picture, should I start the longitude from the far ...
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### Can I retrieve longitude of Lunar Reconnaissance Orbiter around the Moon by POST method (URL)?

I see that I can use an URL like this to retrieve position data for LRO around the Moon: https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&MAKE_EPHEM=%27YES%27&TABLE_TYPE=%27VECTORS%27&...
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### Accuracy of ECEF to ECI, using just GAST

I am working on a Low to Medium fidelity orbit analysis tool. My key factor here is speed, I am analyzing constellations with 500 - 1000 satellites and want to be able to perform the analysis in under ...
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### Rotation matrix from J2000 to ITRF2008

I want to rotate a vector from the inertial J2000 frame into ITRF2008. I am using the NASA SPICE library, which provides a rotation matrix from J2000 to ITRF93 (they plan to upgrade the library to a ...
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### LVLH to ECI Conversion

I'd like to transform LVLH coordinates to ECI coordinates. I've been looking at academic papers and other answers on here and other websites and have only seen the transformation in the other ...
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### Diagram of Hayabusa 2 in "Hill Coordinate System"; what is that exactly? How to convert it to inertial?

These JAXA's Hayabusa-2's two Tweets: 1 2 show a diagram of the spacecraft's motion relative to Ruygu in what they call a Hill Coordinate System, This is a diagram of the trajectory during solar ...
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### How can I convert a Walker constellation (i: t/p/f) to cartesian position and velocity coordinates (ECI)?

I need to convert a Walker constellation (i: t/p/f) to cartesian position and velocity coordinates relative to earth center (ECI) -- i.e., position x,y,z and velocity x,y,z. Standard Anaconda Python ...
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### 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 ...
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### How accurate can a point in space be determined by the likes of the ICRF?

How accurately could a 3D point in open space (i.e. not on an object), say at an elevation of 30,000m above sea level, be located or modelled using the likes of the International Celestial Reference ...
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### Converting Keplerian coordinates into Latitude and Longitude

Introduction My goal is follow up the title of this question and obtain the Earth coordinates (latitude, longitude) from the keplerian coords ...
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### Why was the origin of the Apollo lunar module coordinate system "underground"?

Even stranger than the origin of the Saturn V coordinate system is that of the lunar module: The X-axis station reference measurements (inches) start at a design reference point identified as ...
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### ECEF to LLA Test Numbers

i have a list of GEO x,y,x coordinates and using Justin Mooney's R Script to convert to latitude, longitude, altitude(km). I'm looking for some test case numbers to verify Justin's xyz2lla function ...
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### 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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### Which side of Europa is which?

I understand that Europa is tidally locked* to Jupiter, so there's a Jovianmost longitude on one side and an anti-Jovian longitude on the other. What I can't figure out is which side is which. ...
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### Code to calculate distance between two satellites using their TLE data? [duplicate]

I am not acquainted with astronomy at all. I am developing an computer application which works on TLE data from space-track.org, and calculates things based on them. I need to find distance between ...
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### Transformation between ICRF and Fixed in STK

I am building a satellite orbit propagator in MATLAB and I am using STK as a reference. Comparing TwoBody propagator using RKN78 (MATLAB) with HPOP (degree 1, order 1), I am getting quite good ...
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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 ...
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### Map image (x,y) to spherical coordinates [closed]

What is an efficient method to map image pixels (2D-Cartesian) to their spherical coordinates given camera azimuth and elevation? (Ideally, response includes mathematical notation/Python/C++)
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### Calculating the radial, in-track and cross-track distances

I'm computing the relative distances between satellites. The following picture shows the distances, which are considered as risky. What do Radial, In-track and Cross-track mean and why are 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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### Why would someone use Modified Rodrigues Parameters over Quaternions for spacecraft attitude estimation? And vice versa?

I see quite some papers on spacecraft attitude determination and control, that rely on quaternions. While some others rely on MRPs. The advantage that I see so far is that... for quaternions, the ...
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### Does a solar geometry library exist for satellites in LEO?

I'm looking for a solar geometry library built for a cubesat in LEO. In my research so far, I've discovered the MINES Paris-Tech Solar Geometry 2 library (http://www.oie.mines-paristech.fr/...
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### Spacecraft-fixed coordinate system

I am working with data from a polar-orbiting satellite (inclination 97 degrees) with limited attitude information. I am trying to define a coordinate system which is fixed with respect to the ...
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### Is it possible to plot the ground track of a satellite with just azimuth & elevation angles without range?

I came across this question on StackOverflow about Satellite Trajectory plot. In the code mentioned in the question, the user takes only the Azimuth & Elevation angles (radians) & converts ...
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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 ...
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. ...