1 files changed, 28 insertions, 0 deletions
diff --git a/src/pj_phi2.c b/src/pj_phi2.c
new file mode 100644
index 00000000..dbb79d4d
--- /dev/null
+++ b/src/pj_phi2.c
@@ -0,0 +1,28 @@
+/* determine latitude angle phi-2 */
+#ifndef lint
+static const char SCCSID[]="@(#)pj_phi2.c	4.3	93/06/12	GIE	REL";
+#endif
+#include <projects.h>
+
+#define HALFPI		1.5707963267948966
+#define TOL 1.0e-10
+#define N_ITER 15
+
+	double
+pj_phi2(double ts, double e) {
+	double eccnth, Phi, con, dphi;
+	int i;
+
+	eccnth = .5 * e;
+	Phi = HALFPI - 2. * atan (ts);
+	i = N_ITER;
+	do {
+		con = e * sin (Phi);
+		dphi = HALFPI - 2. * atan (ts * pow((1. - con) /
+		   (1. + con), eccnth)) - Phi;
+		Phi += dphi;
+	} while ( fabs(dphi) > TOL && --i);
+	if (i <= 0)
+		pj_errno = -18;
+	return Phi;
+}