unable to use Aerospace Blockset function eci2ecef

Hi, I need to a function to transform acceleration data from ECI to ECEF frame and I found this function on Aerospace Blockset which does exactly what I need (https://www.mathworks.com/help/aeroblks/eci2ecef.html). However, I was unable to use it within a normal matlab script. I tried one of the example codes from the help center:

r_eci = [-2981784 5207055 3161595];

utc = [2019 1 4 12 0 0];

mjd = mjuliandate(utc);

pm = polarMotion(mjd, 'action', 'none')*180/pi;

r_ecef = eci2ecef(utc, r_eci, 'pm', pm)

And I got the following error:

Unrecognized function or variable 'eci2ecef'.

Is it possible to use this function outiside of Simulink in a normal script? Does anyone knows a good replacement for this function?

Thanks

Answer 1

[Divya Yerraguntla]

Hi Eduardo,

The "eci2ecef" is part of the set of function in CubeSats hence the function requires the 'Aerospace Blockset CubeSat Simulation Library' Add-on support package. You could download this from the Add-ons manager.

Hope it helps!

[Eduardo Rodrigues Silva Filho]

It worked.

Thank you very much!

[lai]

Thank you!

Answer 2

[Seth Wagenman]

Try importing Python's pymap3d package and using it instead as described at:

https://github.com/geospace-code/matmap3d/issues/3#issuecomment-686521080

Unfortunately, you have to convert your MATLAB datetime objects to datenum and then do some math on them before passing over to Python, as described here:

https://github.com/geospace-code/matmap3d/issues/3#issue-690418768

The Python astropy package is the basis for the coordinate transformations and it works quite well. It is a bit slow and I recommend installing the MATLAB API for Python and using a custom Python function which returns MATLAB data objects instead of numpy arrays, which will then require extra conversion within MATLAB anyway before you can use them; see this answer for a work-around if you do not have administrative privileges:

https://www.mathworks.com/matlabcentral/answers/216498-passing-numpy-ndarray-from-python-to-matlab#answer_487604

Hope it works! I would love a comparison between what MATLAB spits out for Null Island's ECI coordinates on January 1, 2000 at noon UTC (using the leap seconds option) to compare. The python code returns (1158174.7900579234, -6272101.938428859, -143.09802467421062).