first draft at a helmert transformation

Author: Nathaniel McHugh

geospatial.c

@@ -35,12 +35,20 @@ ZEND_BEGIN_ARG_INFO_EX(haversine_args, 0, 0, 4)
 	ZEND_ARG_INFO(0, radius)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO_EX(helmert_args, 0, 0, 3)
+    ZEND_ARG_INFO(0, x)
+    ZEND_ARG_INFO(0, y)
+    ZEND_ARG_INFO(0, z)
+ZEND_END_ARG_INFO()
+
 /* {{{ geospatial_functions[]
  *
  * Every user visible function must have an entry in geospatial_functions[].
  */
 const zend_function_entry geospatial_functions[] = {
-	PHP_FE(haversine, haversine_args)
+    PHP_FE(haversine, haversine_args)
+	PHP_FE(helmert, helmert_args)
+    /* End of functions */
 	{ NULL, NULL, NULL }
 };
 /* }}} */
@@ -97,6 +105,46 @@ PHP_MINFO_FUNCTION(geospatial)
 }
 /* }}} */
 
+PHP_FUNCTION(helmert)
+{
+    double x, y, z;
+    double xOut, yOut, zOut;
+    double rX, rY, rZ;
+
+    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ddd", &x, &y, &z) == FAILURE) {
+        return;
+    }
+
+    array_init(return_value);
+    rX = ROTATION_X;
+    rX /= 3600;
+    rX *= GEO_DEG_TO_RAD;
+
+    rY = ROTATION_Y;
+    rY /= 3600;
+    rY *= GEO_DEG_TO_RAD;
+
+    rZ = ROTATION_Z;
+    rZ /= 3600;
+    rZ *= GEO_DEG_TO_RAD;
+
+    xOut = x - (rZ * y) + (rY * z);
+    xOut *= SCALE_CHANGE;
+    xOut += WGS84_OSGB36_X;
+
+    yOut = (rZ * x) + y - (rX * z);
+    yOut *= SCALE_CHANGE;
+    yOut += WGS84_OSGB36_Y;
+
+    zOut = (-rY * x) + (rX * y) + z;
+    zOut *= SCALE_CHANGE;
+    zOut += WGS84_OSGB36_Z;
+
+    add_next_index_double(return_value, xOut);
+    add_next_index_double(return_value, yOut);
+    add_next_index_double(return_value, zOut);
+}
+
 /* {{{ proto haversine(double fromLat, double fromLong, double toLat, double toLong [, double radius ])
  * Calculates the greater circle distance between the two lattitude/longitude pairs */
 PHP_FUNCTION(haversine)

php_geospatial.h

@@ -43,10 +43,25 @@ extern zend_module_entry geospatial_module_entry;
  */
 #define GEO_EARTH_RADIUS 6378.137
 
+#define AIRY_1830_A 6377563.396
+#define AIRY_1830_B 6356256.910
+
+#define WGS84_OSGB36_X -446.448;
+#define WGS84_OSGB36_Y 125.157;
+#define WGS84_OSGB36_Z -542.060;
+
+#define SCALE_CHANGE 1.0000204894;
+
+#define ROTATION_X -0.1502;
+#define ROTATION_Y -0.2470;
+#define ROTATION_Z -0.8421;
+
+
 PHP_MINIT_FUNCTION(geospatial);
 PHP_MINFO_FUNCTION(geospatial);
 
 PHP_FUNCTION(haversine);
+PHP_FUNCTION(helmert);
 
 #endif	/* PHP_GEOSPATIAL_H */
 

tests/helmert.phpt

@@ -0,0 +1,19 @@
+--TEST--
+helmert() function - basic test for helmert forumla
+--FILE--
+<?php
+$x = 3909833.018;
+$y = -147097.1376;
+$z = 5020322.478;
+
+var_dump(helmert($x, $y, $z));
+?>
+--EXPECT--
+array(3) {
+  [0]=>
+  float(3909460.068)
+  [1]=>
+  float(-146987.30)
+  [2]=>
+  float(5019888.07)
+}