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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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Are ECI and ECEF Frames, and Do They Belong to the Geocentric Equatorial Coordinate Systems?

I'm completely confused about the difference between geocentric equatorial coordinate systems, ECI, and ECEF. David Vallado, in his book 'Fundamentals of Astrodynamics and Applications,' mentions that ...
ed190's user avatar
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How does the Gpredict software algorithm track satellites?

I was wondering how Gpredict calculates the ground tracks, Lat, Long and elevation based on a ground station. If I understand correctly, Gpredict takes the values from a TLE (Two-Line Element) set, ...
ed190's user avatar
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How to convert Geocentric Coordinates to ECEF using Skyfield?

I'm trying to obtain ECEF coordinates from geocentric coordinates and then plot the ground track using the subpoint function. Any advice? My objective is to create an accurate ground track. Additional ...
ed190's user avatar
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When solving flight dynamics equations, should the integration variables be set in one or multiple reference frames?

when establishing the differential equations of flight dynamics, I have 2 choices: 1、establish the equations in one coordinate system (e.g. in the earth centered inertial system), then doing the ...
JohnYY's user avatar
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3 votes
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TEME state vector to TLE orbital elements

I was looking at time series of some TLE parameter(semimajor axis, inclination, etc..) and I wanted to how those parameters evolve between measured time points. So i decided to feed TLE element to ...
klobaska soslaninou's user avatar
1 vote
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66 views

Why ECEF does not coincide with ECI on January 1, 2000 at 12.00? [duplicate]

I assumed that ECEF frame coincides with ECI frame on January 1, 2000 at 12.00. To see that, on MATLAB, I used the dcmeci2ecef() function as: ...
ismailhy58's user avatar
3 votes
1 answer
163 views

How can I calculate GPS satellite's Latitude and Longitude if I have the elevation, the azimuth, the XYZ coordinates of the ground station

How can I calculate a GPS satellite's latitude and longitude if the elevation, the azimuth, and the XYZ coordinates of the ground GPS station are provided? I have tried these questions: Computing GEO ...
TThoye's user avatar
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2 answers
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Elevation angle for a non-GEO satellite

I want to calculate the elevation angle of a Non-GEO satellite with respect to a ground terminal. The information I have to solve this: Instantaneous Longitude, Latitude, and Altitude of the non-GEO ...
Black Dagger's user avatar
2 votes
2 answers
934 views

How to calculate the ECEF coordinates of a satellite given its elevation and azimuth angle, plus the coordinates of a reference object on Earth

So I am looking for a way to 'reverse engineer' satellite ECEF coordinates given its angles of elevation and azimuth and given the coordinates of an object on Earth serving as a reference ground. The ...
Akhaim's user avatar
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1 answer
379 views

How to convert TLE data into state vectors in ITRF?

As shown in the question, Now I have a TLE observation data and CPF(Consolidated Prediction Format) data. According to CPF's documentation, CPF predictions are tabulated satellite state vectors ...
inner heart's user avatar
2 votes
1 answer
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Is this a typo in the Python Skyfield API? "International Coordinate Reference Frame (ICRF)"?

In the Python Skyfield library there is a position object skyfield.positionlib.ICRF, in the documentation it states: An (x,y,z) position and velocity oriented to ...
KDecker's user avatar
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At what point on the Earth's surface does the +X axes of the J2000 coordinate system intersect?

From my newly and developing understanding of the J2000 coordinate system it is defined as the point at which the sun appears to cross the celestial equator from the Southern to the Northern ...
KDecker's user avatar
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1 answer
668 views

Where do I find ECEF coordinates of a satellite?

I am taking a university course named 'satellite navigation' as a part of my master degree in aerospace engineering. For the exam we are required to elaborate the coordinates of a LEO satellite (it ...
Giovanni 's user avatar
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1 answer
895 views

Transformation ECI to ECEF acceleration and forces

I know that for velocity conversions between ECI and ECEF there is an $\omega \times r_{ECI} $ term, such that the overall transformation is $v_{ECEF}=v_{ECI}-\omega \times r_{ECI}$. In my belief ...
alexmesa's user avatar
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306 views

How do I convert from one local NED frame to another?

A little bit of background in case you are interested. I am running a re-entry simulation, and I am dealing with two different reference frames. The one with the higher fidelity dynamics is in the ...
alexmesa's user avatar
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77 views

How does one generate a formula(s) for an artificial satellite's location at time t given a set of known locations at discrete times?

Given a set of spatio-temporal points in space {(Lat_1, Lon_1, Alt_1, Time_1), ... (Lat_n, Lon_n, Alt_n, Time_n)}, I need a function (i.e. a formula) that takes these points (or subset of points) as ...
Imp's user avatar
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JWST - coordinates available?

Will the actual coordinates of JWST be made available for download (on an ongoing basis)? It would be interesting to have these, to better understand and appreciate station keeping maneuvers.
Bruce Simonson's user avatar
4 votes
0 answers
144 views

How do you compute horizontal coordinates of a GPS satellite from its broadcast ephemeris?

I'm not an astronomer by any means, and am trying to extract the horizontal coordinates, azimuth and altitude, of a GPS satellite given its most recent broadcast ephemeris. Here is some example ...
Matthew Trotter's user avatar
1 vote
0 answers
8k views

How to calculate Azimuth/Elevation of a satellite?

I have a ground stations' lat/lon as well as a satellite's lat/long. I want to calculate the azimuth/elevation of the satellite relatively to the ground station. Currently, I am using these formulas (...
lawndownunder's user avatar
8 votes
2 answers
568 views

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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1 vote
1 answer
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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?
Sam's user avatar
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3 votes
1 answer
186 views

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 ...
Sun's user avatar
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2 answers
468 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 ...
Martian's user avatar
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4 votes
1 answer
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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 ...
chrishorton's user avatar
3 votes
2 answers
591 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)....
alana's user avatar
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-1 votes
1 answer
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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 ...
uhoh's user avatar
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5 votes
1 answer
125 views

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 ...
WildWilyWilly's user avatar
2 votes
0 answers
343 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 ...
jumpjack's user avatar
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0 votes
1 answer
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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 ...
Nash's user avatar
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1 vote
0 answers
62 views

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 ...
jumpjack's user avatar
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3 votes
1 answer
275 views

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 ...
Shen's user avatar
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0 votes
1 answer
594 views

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 ...
jumpjack's user avatar
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2 votes
1 answer
113 views

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 ...
tdMJN6B2JtUe's user avatar
1 vote
2 answers
1k 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 ...
jos's user avatar
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5 votes
3 answers
2k 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 (...
jos's user avatar
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4 votes
1 answer
311 views

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 ...
Samuel Low's user avatar
5 votes
1 answer
851 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 ...
uhoh's user avatar
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3 votes
0 answers
106 views

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 ...
Elisa Fitri's user avatar
1 vote
2 answers
99 views

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&...
jumpjack's user avatar
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11 votes
4 answers
23k views

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. ...
Elisa Fitri's user avatar
4 votes
1 answer
444 views

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 ...
S moran's user avatar
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2 votes
1 answer
402 views

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 ...
vibe's user avatar
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13 votes
3 answers
542 views

A spacecraft is travelling at X units per hour. But relative to what exactly? Does it depend on the orbit? How?

If I am walking, the ground is stationary, and I move $X \frac{\text{units}}{\text{hour}}$ relative to the ground. If I am in low-Earth orbit, then I am still moving $X \frac{\text{units}}{\text{hour}}...
zoplonix's user avatar
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2 votes
1 answer
1k views

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 ...
orbitalmechanicsnoob's user avatar
0 votes
0 answers
183 views

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 ...
user254657's user avatar
4 votes
1 answer
3k views

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?
vibe's user avatar
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3 votes
0 answers
55 views

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 ...
Spatial Guy's user avatar
2 votes
1 answer
3k views

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 ...
WhiteGlove's user avatar
5 votes
0 answers
358 views

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 ...
DrSheldon's user avatar
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8 votes
1 answer
417 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 ...
Organic Marble's user avatar