I was writing some code to perform some celestial calculations. A lot of it handled changes in positions from certain rotations (orbits, revolutions). There are also instances where time is treated as a rotation (ex: 1 hour of rotation is 15 degrees). The best notation for the rotation depends on what is being done. Here are the rotation notations that might be used.

- Radians
- Degrees
- Decimal Degrees
- Degrees, Minutes, Seconds

- Hours
- Decimal Hours
- Hours, Minutes, Seconds

Conversion from one to another is easy. What I did find challenging is ensuring that the right conversion had been performed before working with it. The trig functions expect to always receive radians. More than once I made the mistake of converting to the wrong unit before performing a calculation. Rather then continue forward on a path that has many opportunities for mistakes I made a single class to represent rotations that can be used in various scenarios. It will always internally represent rotations in degrees. If I want to explicitly convert the class to a specific type there are methods to explicitly convert to any of the other rotation types.

Instances of this custom type also can be assigned a preferred notation. This preferred notation is used when printing it to the output stream. This allows a preferred format to be assigned without risking making any conversion mistakes.

The interface for the class and the support class follows.

#include <stdio.h> #include <cmath> #include <iostream> typedef double Degree; typedef double Hour; typedef double Minute; typedef double Second; typedef double Radian; enum RotationNotation { NOTATION_DEGREES, NOTATION_DMS, NOTATION_HOURS, NOTATION_HMS, NOTATION_RADIANS }; class Rotation; struct HMS { Hour H; Minute M; Second S; }; struct DMS { Degree D; Minute M; Second S; } ; std::ostream& operator << (std::ostream& o, const HMS& h); std::ostream& operator << (std::ostream& o, const DMS& d); std::ostream& operator << (std::ostream& o, const Rotation a); double sin(const Rotation& source); double cos(const Rotation& source); Hour RadToHour(const Radian ); Hour HMSToHour(const HMS& hms); Hour DMSToHour(const DMS&); Hour DegToHour(const Degree degrees); DMS RadToDMS(const Radian); DMS DegToDMS(const Degree degrees); DMS HourToDMS(const Hour hour); DMS HMSToDMS(const HMS&); HMS RadToHMS(const Radian); HMS DegToHMS(const Degree degrees); HMS DMSToHMS(const DMS&); HMS HourToHMS(const Hour); Degree RadToDeg(const Radian); Degree DMSToDeg(const DMS& ); Degree HMSToDeg(const HMS&); Degree HourToDeg(const Hour hour); Radian HourToRad(const Hour); Radian HMSToRad(const HMS& ); Radian DMSToRad(const DMS& ); Radian DegToRad(const Degree); class Rotation { private: Degree _degrees; RotationNotation _notation; public: Rotation(); Rotation(const Rotation& source); RotationNotation getNotation() const; void setNotation(RotationNotation); const Degree getDegrees() const; const Hour getHours() const ; const Minute getRadians() const ; const DMS getDMS() const ; const HMS getHMS() const ; void setDegrees(const Degree degree) ; void setHours(const Hour hour) ; void setRadians(const Radian rad) ; void setDMS(const DMS& dms) ; void setHMS(const HMS& hms) ; };

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