1 files changed, 33 insertions, 0 deletions
diff --git a/src/pj_auth.c b/src/pj_auth.c
new file mode 100644
index 00000000..92ec339b
--- /dev/null
+++ b/src/pj_auth.c
@@ -0,0 +1,33 @@
+/* determine latitude from authalic latitude */
+#ifndef lint
+static const char SCCSID[]="@(#)pj_auth.c	4.3	93/06/12	GIE	REL";
+#endif
+#include <projects.h>
+# define P00 .33333333333333333333
+# define P01 .17222222222222222222
+# define P02 .10257936507936507936
+# define P10 .06388888888888888888
+# define P11 .06640211640211640211
+# define P20 .01641501294219154443
+#define APA_SIZE 3
+	double *
+pj_authset(double es) {
+	double t, *APA;
+
+	if (APA = (double *)pj_malloc(APA_SIZE * sizeof(double))) {
+		APA[0] = es * P00;
+		t = es * es;
+		APA[0] += t * P01;
+		APA[1] = t * P10;
+		t *= es;
+		APA[0] += t * P02;
+		APA[1] += t * P11;
+		APA[2] = t * P20;
+	}
+	return APA;
+}
+	double
+pj_authlat(double beta, double *APA) {
+	double t = beta+beta;
+	return(beta + APA[0] * sin(t) + APA[1] * sin(t+t) + APA[2] * sin(t+t+t));
+}