# 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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### 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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### 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 ...
93 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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### 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 ...
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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 ...
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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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### 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 ...
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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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### 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 ...
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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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### 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 ...
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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 ...
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### 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 ...
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### 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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### TLE SGP4 Coordinate Transformations

I am working on developing a user friendly SGP4 orbit propagator in C on a PIC24. I have extensively read Revisiting Spacetrack Report #3 and celestrak - there are a few outstanding questions I have....
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### Algorithm to convert from ECEF coordinates to ECI coordinates

I am looking for an Algorithm (the formulas; not the code) to convert from ECEF coordinates to ECI coordinates. I have a MATLAB code for it but am unable to understand certain things. So it'd be ...
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### How to calculate the current position of a satellite?

I want to write a SIMULINK model that calculates the position visible of satellites for the current time. As input for the model I have the coordinates of a location, the current time and the ...
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### Computing GEO satellite's longitude from elevation/azimuth from a given latitude/longitude?

This question is a bit of a mix between satellite knowledge and math. Suppose I have the "look angles" (elevation and azimuth) for an otherwise unidentified geostationary satellite, and I would like ...
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### Where to get rectangular coordinates of the solar system planets?

Title, I tried converting the coordinates from here to rectangular but it seems off.
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### What does “Q frame” means in terms of satellite coordinates?

I'm looking at some old satellite documentation which mentions the use of a "Q frame" coordinate system to keep track of the satellite attitude. What does this "Q frame" generally mean in the field of ...
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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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### Regarding the vernal equinox and calculate a TLE code

I am utterly confused as to how the ecliptic co ordinate system works. My understanding is that the vernal equinox is comparable to greenwich for longitude here on earth. But how do we know where the ...
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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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### How to (correctly) rotate this data so the Ecliptic is in the XY plane?

When plotting orbits using the Python package Skyfield, the coordinates are barycentric ICRS. This puts the center of mass of the solar system at the origin, but the $\hat{z}$ axis is tilted about 23° ...
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### How is space mapped out?

Here on earth, we have four directions(East, West, North, South). We have earth maps which shows our exact location from any other location in 2D plane. But in space, planets and stars are in three ...