# 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 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 ...
67 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 ...
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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.
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### 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 ...
388 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 (...
240 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 ...
1 vote
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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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### 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 ...
152 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 ...
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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)....
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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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### 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 ...
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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 ...
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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 ...
1 vote
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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 ...
128 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 ...
377 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 ...
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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 ...
1 vote
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### 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 ...
927 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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### 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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### 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 ...
1 vote
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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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### 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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### 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 ...
461 views

### 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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### 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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### 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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### 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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### 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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### 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 ...
236 views

### 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 ...
1 vote
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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 ...
1 vote
161 views

### 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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### 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 ...
1k views

### 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++)
1 vote
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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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### 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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### 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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### 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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### 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 ...