1 files changed, 18 insertions, 0 deletions
diff --git a/libtellurian_normal_gravity_radians.c b/libtellurian_normal_gravity_radians.c
new file mode 100644
index 0000000..3fdb037
--- /dev/null
+++ b/libtellurian_normal_gravity_radians.c
@@ -0,0 +1,18 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+double
+libtellurian_normal_gravity_radians(double latitude)
+{
+	double a = LIBTELLURIAN_EQUATORIAL_RADIUS;
+	double b = LIBTELLURIAN_POLAR_RADIUS;
+	double neg_e2 = fma(b / a, b / a, -1.0);
+	double ag = a * LIBTELLURIAN_EQUATORIAL_GRAVITY;
+	double bg = b * LIBTELLURIAN_POLAR_GRAVITY;
+	double k = bg / ag - 1.0;
+	double sin2_phi = sin(latitude) * sin(latitude);
+	double num = fma(k, sin2_phi, 1.0);
+	double denom2 = fma(neg_e2, sin2_phi, 1.0);
+	return LIBTELLURIAN_EQUATORIAL_GRAVITY * num / sqrt(denom2);
+}