Earth Treated as a Perfect Sphere in `cartesian_to_geographic_aeqd`

[vlouf]

Hi Team,

The function cartesian_to_geographic_aeqd in pyart/core/transforms.py assumes Earth is a perfect sphere (R=6370997.0), but in reality, Earth is an oblate spheroid (e.g., WGS84 model). This can introduce errors, particularly for latitude calculations (~500m off in my own test).

To Reproduce
Steps to reproduce the behavior:

• Use cartesian_to_geographic_aeqd.
• Compare against geodetic transformation libraries (e.g., pyproj).
• Observe discrepancies due to spherical assumption.

Expected behavior
The current behavior is not ideal. If it stays that way then it needs to be documented. Ideally the conversion should account for Earth’s ellipsoidal shape, using appropriate geodetic formulas.

[zssherman]

@vlouf Thank for opening the issue. I'll need to discuss with @mgrover1 on possible solutions etc.