[Octave-patch-tracker] [patch #10021] [octave forge] (mapping) meridianfwd

[Philip Nienhuis]

Update of patch #10021 (project octave):

             Assigned to:                    None => philipnienhuis         

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Follow-up Comment #4:

Just playing around a bit.

>> [lat, lon] = geodeticfwd (0, 0, [-3600:180:3600], earthRadius * 2 * pi() /
360, "Sphere", "degrees")
lat =
 Columns 1 through 22:
   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1 
-1   1  -1
 Columns 23 through 41:
   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1  -1   1

lon =
 Columns 1 through 6:
   2.4495e-15   1.2261e-15   2.2045e-15   1.4710e-15   1.9596e-15  
1.7160e-15
 Columns 7 through 12:
   1.7146e-15   1.9609e-15   1.4697e-15   2.2059e-15   1.2247e-15 
-1.1023e-15
 Columns 13 through 18:
   9.7978e-16  -8.5731e-16   7.3484e-16  -6.1237e-16   4.8989e-16 
-3.6742e-16
 Columns 19 through 24:
   2.4495e-16  -1.2247e-16            0   1.2247e-16  -2.4495e-16  
3.6742e-16
 Columns 25 through 30:
  -4.8989e-16   6.1237e-16  -7.3484e-16   8.5731e-16  -9.7978e-16  
1.1023e-15
 Columns 31 through 36:
  -1.2247e-15  -2.2059e-15  -1.4697e-15  -1.9609e-15  -1.7146e-15 
-1.7160e-15
 Columns 37 through 41:
  -1.9596e-15  -1.4710e-15  -2.2045e-15  -1.2261e-15  -2.4495e-15


==> looks worthwile to wrapTo180 / wrapToPi the azimuth argument behind the
scenes in order to limit the max error.

Then,

>> [lat, lon] = geodeticfwd (0, 0, [-360:180:360], earthRadius * 2 * pi() / 4,
"Sphere", "degrees")
lat =
   90  -90   90  -90   90

lon =
 Columns 1 through 3:
    90.0000 - 118.2262i   -90.0000 +  75.4561i          0 +        0i
 Columns 4 and 5:
    90.0000 -  75.4561i   -90.0000 + 118.2262i


... nasty, complex output. I suspect this corner case (moving from equator to
the poles) needs better preprocessing around Ls. 143-144.

Moving from the poles to the equator goes better:

>> [lat, lon] = geodeticfwd (90, 0, [-360:180:360], earthRadius * 2 * pi() /
4, "Sphere", "degrees")
lat =
   7.0165e-15            0   7.0165e-15            0   7.0165e-15

lon =
   1.4033e-14  -7.0165e-15            0   7.0165e-15  -1.4033e-14


This is just with a spherical Earth model, haven't tried ellipsoids yet.

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