Emmanuel Giasson created SIS-537:
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Summary: wrong longitude in reverse Oblique Stereographic
transform
Key: SIS-537
URL: https://issues.apache.org/jira/browse/SIS-537
Project: Spatial Information Systems
Issue Type: Bug
Components: Referencing
Affects Versions: 1.1
Reporter: Emmanuel Giasson
The Oblique Stereographic transform projects just fine in forward, but the
reverse transform offset almost half the longitudes by nearly 180 degrees.
h2. Bug location and suggested fix
Problem seems to be in
{{org/apache/sis/referencing/operation/projection/ObliqueStereographic.java}}
method {{inverseTransform(...)}}
{{ ...}}
{{ final double i = atan(x / (h + y));
final double j = atan(x / (g - y)) - i;
...
final double λ = j + 2*i}}
EPSG Guidance notes (for instance, p.71 of
[https://www.iogp.org/wp-content/uploads/2019/09/373-07-02.pdf)] uses atan2
instead of atan, which effectively fix the +/- 180 degrees issue in this case.
Actually, it's not exactly 180 degrees since {{i}} might be correct with either
atan or atan2, and only {{j}} might be 180 degrees off.
h2. To reproduce
With the following transformation, project POINT(30 45) then reverse project.
Result is POINT(-149.84855267371876 45.000000000000014)
Param_MT["Oblique Stereographic",
Parameter["semi_major", 6378137.0, Unit["metre", 1]],
Parameter["semi_minor", 6356752.314245179, Unit["metre", 1]],
Parameter["Latitude of natural origin", 45.0, Unit["degree",
0.017453292519943295]],
Parameter["Longitude of natural origin", -70.0, Unit["degree",
0.017453292519943295]]]
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