wind_dir.c File Reference

The compass direction a wind is blowing from, as a bearing and as a sideways component. More...

#include "weather/wind_dir.h"
#include <ctype.h>
#include <stdbool.h>
#include <stddef.h>

Macros
#define	POINT_COUNT   16
	How many compass points a direction can name, from N through NNW.

Functions
static bool	same_point (const char *a, const char *b)
	Whether two compass abbreviations are the same, ignoring case.
static int	sin_milli (int degrees)
	Sine in thousandths, from a table every 15 degrees with the gaps interpolated.
int	wind_bearing (const char *dir)
	The bearing a 16-point compass abbreviation stands for.
int	wind_lean (int bearing)
	The east-west component of a wind, as a signed proportion.

Detailed Description

The compass direction a wind is blowing from, as a bearing and as a sideways component.

Function Documentation

same_point()

bool same_point ( const char * a, const char * b )

static

Whether two compass abbreviations are the same, ignoring case.

Parameters

a	The first abbreviation.
b	The second abbreviation.

Returns

Whether they match, case insensitive.

sin_milli()

int sin_milli ( int degrees )

static

Sine in thousandths, from a table every 15 degrees with the gaps interpolated.

The watch has a trig lookup but this file is pure core and cannot reach it, and pulling float maths in for one component would cost more than the table does. Straight lines between fifteen-degree stops land within a percent of a real sine, which is finer than a caller working in whole pixels or whole percent can use.

Parameters

degrees

The angle to take the sine of. Wrapped into 0 to 359 first, negative values included.

Returns

The sine of the angle, times 1000.