On Thu, Mar 26, 2015 at 5:35 PM, Bonneau, Olivier (EXP) <
olivier.bonn...@lmco.com> wrote:
> Hi all,
>
>
>
> I'm interested in the calculation of Loxodromes i.e Rhumb Line (a line of
> constant azimuth on the surface of the ellipsoid).
>
> Anyone would know how to do it using Geotools library ?
>
The GeodeticCalculator class has a getLoxodromicCurve method, but it seems
that its internal code is
wrong, and has a large comment here:
if (true) {
throw new UnsupportedOperationException();
}
/*************************************************************************************
** THE FOLLOWING IS CHECKED FOR COMPILER ERROR, BUT EXCLUDED FROM
THE .class FILE. **
** THIS CODE IS WRONG: LOXODROMIC CURVES ARE STRAIGHT LINES IN
MERCATOR PROJECTION, **
** NOT IT PLAIN (longitude,latitude) SPACE. FURTHERMORE, THE "OUT
OF BOUNDS" CHECK **
** IS UNFINISHED: WHEN THE PATH CROSS THE 180° LONGITUDE, A +360°
ADDITION NEED TO **
** BE PERFORMED ON ONE OF THE SOURCE OR TARGET POINT BEFORE TO
COMPUTE THE LINEAR **
** INTERPOLATION (OTHERWISE, THE SLOPE VALUE IS WRONG). FORMULAS
FOR COMPUTING MID- **
** POINT ON A LOXODROMIC CURVE ARE AVAILABLE THERE:
**
**
**
** http://mathforum.org/discuss/sci.math/a/t/180912
**
**
**
** LatM = (Lat0+Lat1)/2
**
**
**
** (Lon1-Lon0)log(f(LatM)) + Lon0 log(f(Lat1)) - Lon1
log(f(Lat0)) **
** LonM =
--------------------------------------------------------------- **
** log(f(Lat1)/f(Lat0))
**
**
**
** where log(f(x)) == log(sec(x)+tan(x)) is the inverse
Gudermannian function. **
*************************************************************************************/
Soo... I guess we don't have a way to compute a loxodrome after all...
although from the math above,
it seems it would not be too hard to implement a correct version of this
method
Cheers
Andrea
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