[Rtk-users] itFirstAngle and itLastAngle in rtkParkerShortScanImageFilter.txt

[Andy Shieh]

Hi Simon & RTK developers & the RTK community,

I have a question about how delta is calculated in
rtkParkerShortScanImageFilter.txt.

The itFirstAngle and the itLastAngle were used to find the first and last
angular values for calculating delta.

However I noticed that at line 93 itFirstAngle is acquired by:

  itFirstAngle = sortedAngles.find(rotationAngles[maxAngularGapPos]);
  itFirstAngle =
(++itFirstAngle==sortedAngles.end())?sortedAngles.begin():itFirstAngle;
  itFirstAngle =
(++itFirstAngle==sortedAngles.end())?sortedAngles.begin():itFirstAngle;

Why are the second and third lines duplicated? Wouldn't this point to the
"second" angle instead?

And also for itLastAngle at line 99:

  itLastAngle = sortedAngles.find(rotationAngles[maxAngularGapPos]);
  itLastAngle =
(itLastAngle==sortedAngles.begin())?--sortedAngles.end():--itLastAngle;

Why is the second line needed here? Wouldn't this point to the "second
last" angle instead? (Since maxAngularGapPos was caluclated
with GetAngularGapsWithNext).

I did test this with a 0-200 deg short scan, and found that firatAngle and
lastAngle weren't equal to 0 and 200, but were calculated to be the second
and second last angles instead.
Is there any reason for this implementation?

Thank you.

Cheers,
Andy
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