Add Update the World Magnetic Model to 2015.0

diff --git a/simgear/magvar/coremag.cxx b/simgear/magvar/coremag.cxx
index 8d0616fd33f9ebb46762b1d54952cb14fcb938ec..c5aa08b15af9c135584de54f33e26132c9f376a0 100644 (file)
--- a/simgear/magvar/coremag.cxx
+++ b/simgear/magvar/coremag.cxx
@@ -24,10 +24,10 @@
 // Put in some bullet-proofing to handle magnetic and geographic poles.
 // 3/28/2000 EAW
 //
-// Updated coefficient arrays to use the current WMM2005 model,
+// Updated coefficient arrays to use the current wmm2005 model,
 // (valid between 2005.0 and 2010.0)
 // Also removed unused variables and corrected earth radii constants
-// to the values for WGS84 and WMM2005.
+// to the values for WGS84 and wmm2005.
 // Reference:
 //     McLean, S., S. Macmillan, S. Maus, V. Lesur, A.
 //     Thomson, and D. Dater, December 2004, The
@@ -36,6 +36,20 @@
 //
 // 25/10/2006  Wim Van Hoydonck -- wim.van.hoydonck@gmail.com
 //
+//
+// Updated coefficient arrays to use the current wmm2015 model,
+// (valid between 2015.0 and 2020.0)
+// Also removed unused variables and corrected earth radii constants
+// to the values for WGS84 and wmm2015.
+// Reference:
+//     A. Chulliat , S. Macmillan, P. Alken, C. Beggan, M.
+//     Nair, B. Hamilton, A. Woods, V. Ridley,
+//     S Maus, and A Thomson, December 2014, The
+//     US/UK World Magnetic Model for 2015-2020,
+//     NOAA Technical Report WMM2015_Report.pdf
+//
+// 18/06/2015  Jean-Paul Anceaux -- j.p.r.anceaux@gmail.com
+
 
 //  The routine uses a spherical harmonic expansion of the magnetic
 // potential up to twelfth order, together with its time variation, as
@@ -52,7 +66,7 @@
 // the magnetic poles (where it is ill-defined) where the error may reach
 // 4 degrees or more.
 //
-//   Variation is undefined at both the geographic and  
+//   Variation is undefined at both the geographic and
 // magnetic poles, even though the field itself is well-behaved. To
 // avoid the routine blowing up, latitude entries corresponding to
 // the geographic poles are slightly offset. At the magnetic poles,
@@ -90,72 +104,72 @@ static const double a = 6378.137;       /* semi-major axis (equatorial radius) o
 static const double b = 6356.7523142;   /* semi-minor axis referenced to the WGS84 ellipsoid */
 static const double r_0 = 6371.2;      /* standard Earth magnetic reference radius  */
 
-static double gnm_wmm2005[13][13] =
+static double gnm_wmm2015[13][13] =
 {
     {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-29556.8, -1671.7, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-2340.6, 3046.9, 1657.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {1335.4, -2305.1, 1246.7, 674.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {919.8, 798.1, 211.3, -379.4, 100.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-227.4, 354.6, 208.7, -136.5, -168.3, -14.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {73.2, 69.7, 76.7, -151.2, -14.9, 14.6, -86.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {80.1, -74.5, -1.4, 38.5, 12.4, 9.5, 5.7, 1.8, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {24.9, 7.7, -11.6, -6.9, -18.2, 10.0, 9.2, -11.6, -5.2, 0.0, 0.0, 0.0, 0.0},
-    {5.6, 9.9, 3.5, -7.0, 5.1, -10.8, -1.3, 8.8, -6.7, -9.1, 0.0, 0.0, 0.0},
-    {-2.3, -6.3, 1.6, -2.6, 0.0, 3.1, 0.4, 2.1, 3.9, -0.1, -2.3, 0.0, 0.0},
-    {2.8, -1.6, -1.7, 1.7, -0.1, 0.1, -0.7, 0.7, 1.8, 0.0, 1.1, 4.1, 0.0},
-    {-2.4, -0.4, 0.2, 0.8, -0.3, 1.1, -0.5, 0.4, -0.3, -0.3, -0.1, -0.3, -0.1},
+    {-29438.5, -1501.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-2445.3, 3012.5, 1676.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {1351.1, -2352.3, 1225.6, 581.9, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {907.2, 813.7, 120.3, -335.0, 70.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-232.6, 360.1, 192.4, -141.0, -157.4, 4.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {69.5, 67.4, 72.8, -129.8, -29.0, 13.2, -70.9, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {81.6, -76.1, -6.8, 51.9, 15.0, 9.3, -2.8, 6.7, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {24.0, 8.6, -16.9, -3.2, -20.6, 13.3, 11.7, -16.0, -2.0, 0.0, 0.0, 0.0, 0.0},
+    {5.4, 8.8, 3.1, -3.1, 0.6, -13.3, -0.1, 8.7, -9.1, -10.5, 0.0, 0.0, 0.0},
+    {-1.9, -6.5, 0.2, 0.6, -0.6, 1.7, -0.7, 2.1, 2.3, -1.8, -3.6, 0.0, 0.0},
+    {3.1, -1.5, -2.3, 2.1, -0.9, 0.6, -0.7, 0.2, 1.7, -0.2, 0.4, 3.5, 0.0},
+    {-2.0, -0.3, 0.4, 1.3, -0.9, 0.9, 0.1, 0.5, -0.4, -0.4, 0.2, -0.9, 0.0},
 };
 
-static double hnm_wmm2005[13][13]=
+static double hnm_wmm2015[13][13]=
 {
     {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 5079.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -2594.7, -516.7, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -199.9, 269.3, -524.2, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 281.5, -226.0, 145.8, -304.7, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 42.4, 179.8, -123.0, -19.5, 103.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -20.3, 54.7, 63.6, -63.4, -0.1, 50.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -61.5, -22.4, 7.2, 25.4, 11.0, -26.4, -5.1, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 11.2, -21.0, 9.6, -19.8, 16.1, 7.7, -12.9, -0.2, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -20.1, 12.9, 12.6, -6.7, -8.1, 8.0, 2.9, -7.9, 6.0, 0.0, 0.0, 0.0},
-    {0.0, 2.4, 0.2, 4.4, 4.8, -6.5, -1.1, -3.4, -0.8, -2.3, -7.9, 0.0, 0.0},
-    {0.0, 0.3, 1.2, -0.8, -2.5, 0.9, -0.6, -2.7, -0.9, -1.3, -2.0, -1.2, 0.0},
-    {0.0, -0.4, 0.3, 2.4, -2.6, 0.6, 0.3, 0.0, 0.0, 0.3, -0.9, -0.4, 0.8},
+    {0.0, 4796.2, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -2845.6, -642.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -115.3, 245.0, -538.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 283.4, -188.6, 180.9, -329.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 47.4, 196.9, -119.4, 16.1, 100.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -20.7, 33.2, 58.8, -66.5, 7.3, 62.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -54.1, -19.4, 5.6, 24.4, 3.3, -27.5, -2.3, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 10.2, -18.1, 13.2, -14.6, 16.2, 5.7, -9.1, 2.2, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -21.6, 10.8, 11.7, -6.8, -6.9, 7.8, 1.0, -3.9, 8.5, 0.0, 0.0, 0.0},
+    {0.0, 3.3, -0.3, 4.6, 4.4, -7.9, -0.6, -4.1, -2.8, -1.1, -8.7, 0.0, 0.0},
+    {0.0, -0.1, 2.1, -0.7, -1.1, 0.7, -0.2, -2.1, -1.5, -2.5, -2.0, -2.3, 0.0},
+    {0.0, -1.0, 0.5, 1.8, -2.2, 0.3, 0.7, -0.1, 0.3, 0.2, -0.9, -0.2, 0.7},
 };
 
-static double gtnm_wmm2005[13][13]=
+static double gtnm_wmm2015[13][13]=
 {
     {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {8.0, 10.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-15.1, -7.8, -0.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.4, -2.6, -1.2, -6.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-2.5, 2.8, -7.0, 6.2, -3.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-2.8, 0.7, -3.2, -1.1, 0.1, -0.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {-0.7, 0.4, -0.3, 2.3, -2.1, -0.6, 1.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.2, -0.1, -0.3, 1.1, 0.6, 0.5, -0.4, 0.6, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.1, 0.3, -0.4, 0.3, -0.3, 0.2, 0.4, -0.7, 0.4, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {10.7, 17.9, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-8.6, -3.3, 2.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {3.1, -6.2, -0.4, -10.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-0.4, 0.8, -9.2, 4.0, -4.2, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-0.2, 0.1, -1.4, 0.0, 1.3, 3.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {-0.5, -0.2, -0.6, 2.4, -1.1, 0.3, 1.5, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.2, -0.2, -0.4, 1.3, 0.2, -0.4, -0.9, 0.3, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 0.1, -0.5, 0.5, -0.2, 0.4, 0.2, -0.4, 0.3, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -0.1, -0.1, 0.4, -0.5, -0.2, 0.1, 0.0, -0.2, -0.1, 0.0, 0.0, 0.0},
+    {0.0, 0.0, -0.1, 0.3, -0.1, -0.1, -0.1, 0.0, -0.2, -0.1, -0.2, 0.0, 0.0},
+    {0.0, 0.0, -0.1, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -0.1, -0.1, 0.0},
+    {0.1, 0.0, 0.0, 0.1, -0.1, 0.0, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
 };
 
-static double htnm_wmm2005[13][13]=
+static double htnm_wmm2015[13][13]=
 {
     {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -20.9, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -23.2, -14.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 5.0, -7.0, -0.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 2.2, 1.6, 5.8, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 1.7, 2.1, 4.8, -1.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -0.6, -1.9, -0.4, -0.5, -0.3, 0.7, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.6, 0.4, 0.2, 0.3, -0.8, -0.2, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, -0.2, 0.1, 0.3, 0.4, 0.1, -0.2, 0.4, 0.4, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
-    {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -26.8, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -27.1, -13.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 8.4, -0.4, 2.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -0.6, 5.3, 3.0, -5.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 0.4, 1.6, -1.1, 3.3, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 0.0, -2.2, -0.7, 0.1, 1.0, 1.3, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, 0.7, 0.5, -0.2, -0.1, -0.7, 0.1, 0.1, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -0.3, 0.3, 0.3, 0.6, -0.1, -0.2, 0.3, 0.0, 0.0, 0.0, 0.0, 0.0},
+    {0.0, -0.2, -0.1, -0.2, 0.1, 0.1, 0.0, -0.2, 0.4, 0.3, 0.0, 0.0, 0.0},
+    {0.0, 0.1, -0.1, 0.0, 0.0, -0.2, 0.1, -0.1, -0.2, 0.1, -0.1, 0.0, 0.0},
+    {0.0, 0.0, 0.1, 0.0, 0.1, 0.0, 0.0, 0.1, 0.0, -0.1, 0.0, -0.1, 0.0},
+    {0.0, 0.0, 0.0, -0.1, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
 };
 
 static const int nmax = 12;
@@ -174,7 +188,7 @@ static double roots[13][13][2];
 unsigned long int yymmdd_to_julian_days( int yy, int mm, int dd )
 {
     unsigned long jd;
- 
+
     yy = (yy < 50) ? (2000 + yy) : (1900 + yy);
     jd = dd - 32075L + 1461L * (yy + 4800L + (mm - 14) / 12 ) / 4;
     jd = jd + 367L * (mm - 2 - (mm - 14) / 12*12) / 12;
@@ -182,7 +196,7 @@ unsigned long int yymmdd_to_julian_days( int yy, int mm, int dd )
 
     /* printf("julian date = %d\n", jd ); */
     return jd;
-} 
+}
 
 
 /*
@@ -196,7 +210,7 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
     /* output field B_r,B_th,B_phi,B_x,B_y,B_z */
     int n,m;
     /* reference date for current model is 1 januari 2005 */
-    long date0_wmm2005 = yymmdd_to_julian_days(5,1,1);
+    long date0_wmm2015 = yymmdd_to_julian_days(5,1,1);
 
     double yearfrac,sr,r,theta,c,s,psi,fn,fn_0,B_r,B_theta,B_phi,X,Y,Z;
     double sinpsi, cospsi, inv_s;
@@ -215,7 +229,7 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
     /* theta is geocentric co-latitude */
 
     r = h*h + 2.0*h * sr +
-       (a*a*a*a - ( a*a*a*a - b*b*b*b ) * sinlat*sinlat ) / 
+       (a*a*a*a - ( a*a*a*a - b*b*b*b ) * sinlat*sinlat ) /
        (a*a - (a*a - b*b) * sinlat*sinlat );
 
     r = sqrt(r);
@@ -224,7 +238,7 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
     c = cos(theta);
     s = sin(theta);
     /* protect against zero divide at geographic poles */
-    inv_s =  1.0 / (s + (s == 0.)*1.0e-8); 
+    inv_s =  1.0 / (s + (s == 0.)*1.0e-8);
 
     /* zero out arrays */
     for ( n = 0; n <= nmax; n++ ) {
@@ -283,12 +297,12 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
 
     /* compute Gauss coefficients gnm and hnm of degree n and order m for the desired time
        achieved by adjusting the coefficients at time t0 for linear secular variation */
-    /* WMM2005 */
-    yearfrac = (dat - date0_wmm2005) / 365.25;
+    /* wmm2015 */
+    yearfrac = (dat - date0_wmm2015) / 365.25;
     for ( n = 1; n <= nmax; n++ ) {
        for ( m = 0; m <= nmax; m++ ) {
-           gnm[n][m] = gnm_wmm2005[n][m] + yearfrac * gtnm_wmm2005[n][m];
-           hnm[n][m] = hnm_wmm2005[n][m] + yearfrac * htnm_wmm2005[n][m];
+           gnm[n][m] = gnm_wmm2015[n][m] + yearfrac * gtnm_wmm2015[n][m];
+           hnm[n][m] = hnm_wmm2015[n][m] + yearfrac * htnm_wmm2015[n][m];
        }
     }
 
@@ -310,7 +324,7 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
        double c2_n=0;
        double c3_n=0;
        for ( m = 0; m <= n; m++ ) {
-           double tmp = (gnm[n][m] * cm[m] + hnm[n][m] * sm[m]); 
+           double tmp = (gnm[n][m] * cm[m] + hnm[n][m] * sm[m]);
            c1_n=c1_n + tmp * P[n][m];
            c2_n=c2_n + tmp * DP[n][m];
            c3_n=c3_n + m * (gnm[n][m] * sm[m] - hnm[n][m] * cm[m]) * P[n][m];
@@ -340,7 +354,7 @@ double calc_magvar( double lat, double lon, double h, long dat, double* field )
     /* find variation in radians */
     /* return zero variation at magnetic pole X=Y=0. */
     /* E is positive */
-    return (X != 0. || Y != 0.) ? atan2(Y, X) : (double) 0.;  
+    return (X != 0. || Y != 0.) ? atan2(Y, X) : (double) 0.;
 }
 
 
@@ -350,7 +364,7 @@ double SGMagVarOrig( double lat, double lon, double h, long dat, double* field )
     /* output field B_r,B_th,B_phi,B_x,B_y,B_z */
     int n,m;
     /* reference dates */
-    long date0_wmm2005 = yymmdd_to_julian_days(5,1,1);
+    long date0_wmm2015 = yymmdd_to_julian_days(5,1,1);
 
     double yearfrac,sr,r,theta,c,s,psi,fn,B_r,B_theta,B_phi,X,Y,Z;
 
@@ -362,7 +376,7 @@ double SGMagVarOrig( double lat, double lon, double h, long dat, double* field )
     /* theta is geocentric co-latitude */
 
     r = h * h + 2.0*h * sr +
-       (pow(a,4.0) - (pow(a,4.0) - pow(b,4.0)) * pow(sin(lat),2.0)) / 
+       (pow(a,4.0) - (pow(a,4.0) - pow(b,4.0)) * pow(sin(lat),2.0)) /
        (a * a - (a * a - b * b) * pow(sin(lat),2.0));
 
     r = sqrt(r);
@@ -407,12 +421,12 @@ double SGMagVarOrig( double lat, double lon, double h, long dat, double* field )
     }
 
     /* compute gnm, hnm at dat */
-    /* WMM2005 */
-    yearfrac = (dat - date0_wmm2005) / 365.25;
+    /* wmm2015 */
+    yearfrac = (dat - date0_wmm2015) / 365.25;
     for ( n = 1; n <= nmax; n++ ) {
        for ( m = 0; m <= nmax; m++ ) {
-           gnm[n][m] = gnm_wmm2005[n][m] + yearfrac * gtnm_wmm2005[n][m];
-           hnm[n][m] = hnm_wmm2005[n][m] + yearfrac * htnm_wmm2005[n][m];
+           gnm[n][m] = gnm_wmm2015[n][m] + yearfrac * gtnm_wmm2015[n][m];
+           hnm[n][m] = hnm_wmm2015[n][m] + yearfrac * htnm_wmm2015[n][m];
        }
     }