Martin Desruisseaux created SIS-467:
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Summary: Unsupported geodesics
Key: SIS-467
URL: https://issues.apache.org/jira/browse/SIS-467
Project: Spatial Information Systems
Issue Type: Bug
Components: Referencing
Affects Versions: 1.0
Reporter: Martin Desruisseaux
The {{GeodesicOnEllipsoid}} class tries to implement the equations published in
Charles F. F. Karney, 2013. [Algorithms for
geodesics|https://doi.org/10.1007/s00190-012-0578-z], SRI International. Those
algorithms were already implemented in
[GeographicLib|https://geographiclib.sourceforge.io/], which we use as a
reference implementation in our tests but not in the main code in order to keep
the amount of Apache SIS dependencies low. We also want close integration with
the rest of SIS framework (automatic conversion of input/output coordinates),
keep some intermediate values for computing Bezier curves, _etc._ However our
current implementation has the following limitations (maybe because of
misunderstanding on our side). The GeographicLib source code may be examined
for understanding what we are doing wrong, but the relationships between that
source code and the formulas are not easy to establish.
h2. Nearly antipodal geodesics on equator
Apache SIS does not have a solution for geodesics on equator when the
difference of longitude is ∆λ > (1 - _f_)⋅π (close to 180°). This issue is
discussed in Karney (2013) below equation 44, but we have not yet understood
what is the appropriate action. Even if equation 57 can be use for computing α₁
in such case, we still have equations 11 and 12, for example σ = atan2(sinβ,
cosα⋅cosβ), producing 0 because sinβ = 0, which result in a geodesic distance
of 0. We surely do something wrong, but I haven't understood what yet. Current
SIS implementation throws {{IllegalStateException}} in such case.
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