Написание документации: кватернионы и версоры

docs/angle-eng.md

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+# Angles
+
+There are no structures for angles in the library. The library represents
+angles as floating point numbers of types **float** and **double**.
+
+There are three units of measurement for angles in the library:
+* radians (the full round is equal to 2π radians)
+* degrees (the full round is equal to 360 degrees)
+* turns (the full round is equal to 1 turn)
+
+The units of measurement of angles are defined with an enumerated type:
+
+    typedef enum {
+        BG_ANGLE_UNIT_RADIANS = 1,
+        BG_ANGLE_UNIT_DEGREES = 2,
+        BG_ANGLE_UNIT_TURNS   = 3
+    } angle_unit_t;
+
+* BG_ANGLE_UNIT_RADIANS is for measurement of angles in radians
+* BG_ANGLE_UNIT_DEGREES is for measurement of angles in degrees
+* BG_ANGLE_UNIT_TURNS is for measurement of angles in turns
+
+The functions of the library do not require angle values to be limited by any
+range. But there are functions which can normalize angles to specific ranges.
+
+There are two ranges of normalized angles: a signed range and an unsigned
+range.
+
+The unsigned range has no negative values. The unsigned range corresponds:
+* [0, 2π) radians
+* [0, 360) degrees
+* [0, 1) turns
+
+The signed range has both positive and negative values. The signed range
+corresponds:
+* (-π, π] radians
+* (-180, 180] degrees
+* (-0.5, 0.5] turns
+
+The ranges of angles are defined with an enumerated type:
+
+    typedef enum {
+        BG_ANGLE_RANGE_UNSIGNED = 1,
+        BG_ANGLE_RANGE_SIGNED = 2
+    } angle_range_t;
+
+* BG_ANGLE_RANGE_UNSIGNED is for the unsigned range of values;
+* BG_ANGLE_RANGE_SIGNED is for the signed range of values.