From 1760dafbabb12a6486a928c8d5e8a376a2fe5271 Mon Sep 17 00:00:00 2001
From: Kurt Schwehr <schwehr@google.com>
Date: Thu, 3 May 2018 22:59:30 -0700
Subject: Minor cleanup of pj_phi2.c

- tabs -> spaces
- IWYU
- #define -> static const typed
- Combine definition and initialization
- Define one var per statement
- Use the defined symbol rather than embedding bare literals
  -18 -> PJD_ERR_NON_CON_INV_PHI2

Subset of fixes discussed in #971
---
 src/pj_phi2.c | 48 +++++++++++++++++++++++++-----------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

(limited to 'src')

diff --git a/src/pj_phi2.c b/src/pj_phi2.c
index 00b73f70..5f73d510 100644
--- a/src/pj_phi2.c
+++ b/src/pj_phi2.c
@@ -1,28 +1,30 @@
-/* determine latitude angle phi-2 */
+/* Determine latitude angle phi-2. */
+
+#include <math.h>
+
 #include "projects.h"
 
-#define TOL 1.0e-10
-#define N_ITER 15
+static const double TOL = 1.0e-10;
+static const int N_ITER = 15;
+
+double pj_phi2(projCtx ctx, double ts, double e) {
+    double eccnth = .5 * e;
+    double Phi = M_HALFPI - 2. * atan(ts);
+    double con;
+    int i = N_ITER;
+
+    for(;;) {
+        con = e * sin(Phi);
+        double dphi = M_HALFPI - 2. * atan(ts * pow((1. - con) /
+           (1. + con), eccnth)) - Phi;
 
-	double
-pj_phi2(projCtx ctx, double ts, double e) {
-	double eccnth, Phi, con;
-	int i;
+        Phi += dphi;
 
-	eccnth = .5 * e;
-	Phi = M_HALFPI - 2. * atan (ts);
-	i = N_ITER;
-	for(;;) {
-		double dphi;
-		con = e * sin (Phi);
-		dphi = M_HALFPI - 2. * atan (ts * pow((1. - con) /
-		   (1. + con), eccnth)) - Phi;
-		Phi += dphi;
-		if( fabs(dphi) > TOL && --i )
-			continue;
-                break;
-	}
-	if (i <= 0)
-		pj_ctx_set_errno( ctx, -18 );
-	return Phi;
+        if (fabs(dphi) > TOL && --i)
+            continue;
+        break;
+    }
+    if (i <= 0)
+        pj_ctx_set_errno(ctx, PJD_ERR_NON_CON_INV_PHI2);
+    return Phi;
 }
-- 
cgit v1.2.3


From 8e53bdeae08ef8c1a2f0dbf4921b8aa7cc41aa41 Mon Sep 17 00:00:00 2001
From: Kurt Schwehr <schwehr@google.com>
Date: Fri, 4 May 2018 22:44:44 -0700
Subject: Add documentation to pj_phi2 by cffk@

---
 src/pj_phi2.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'src')

diff --git a/src/pj_phi2.c b/src/pj_phi2.c
index b55d9690..a83302e6 100644
--- a/src/pj_phi2.c
+++ b/src/pj_phi2.c
@@ -7,7 +7,22 @@
 static const double TOL = 1.0e-10;
 static const int N_ITER = 15;
 
+/*****************************************************************************/
 double pj_phi2(projCtx ctx, double ts, double e) {
+/******************************************************************************
+Determine latitude angle phi-2.
+Inputs:
+  ts = exp(-psi) where psi is the isometric latitude (dimensionless)
+  e = eccentricity of the ellipsoid (dimensionless)
+Output:
+  phi = geographic latitude (radians)
+Here isometric latitude is defined by
+  psi = log( tan(pi/4 + phi/2) *
+             ( (1 - e*sin(phi)) / (1 + e*sin(phi)) )^(e/2) )
+      = asinh(tan(phi)) - e * atanh(e * sin(phi))
+This routine inverts this relation using the iterative scheme given
+by Snyder (1987), Eqs. (7-9) - (7-11)
+*******************************************************************************/
     double eccnth = .5 * e;
     double Phi = M_HALFPI - 2. * atan(ts);
     double con;
-- 
cgit v1.2.3