PHP Cookbook

2.12. Doing Trigonometry in Degrees, not Radians

Problem

You have numbers in degrees but want to use the trigonometric functions.

Solution

Use deg2rad( ) and rad2deg( ) on your input and output:

$cosine = rad2deg(cos(deg2rad($degree)));

Discussion

By definition, 360 degrees is equal to 2π radians, so it’s easy to manually convert between the two formats. However, these functions use PHP’s internal value of π, so you’re assured a high-precision answer. To access this number for other calculations, use the constant M_PI, which is 3.14159265358979323846.

There is no built-in support for gradians. This is considered a feature, not a bug.

See Also

Recipe 2.13 for trig basics; documentation on deg2rad( ) at http://www.php.net/deg2rad and rad2deg( ) at http://www.php.net/rad2deg.