Add TranverseMercator distance calculations to complement the existin…

…g lat/long implementation

TransverseMercator.php

@@ -257,4 +257,25 @@ public function convertToLatitudeLongitude($N, $E, $N0, $E0, $phi0, $lambda0)
 
  return new LatLng(rad2deg($phi), rad2deg($lambda), 0, $refEll);
  }
+
+ /**
+ * Calculate the surface distance between this object and the one
+ * passed in as a parameter.
+ *
+ * @param self $to object to measure the distance to
+ * @return float
+ */
+ public function distance(self $to) {
+
+ if ($this->refEll != $to->refEll) {
+ throw new \RuntimeException('Source and destination co-ordinates are not using the same ellipsoid');
+ }
+
+ //Because this is a 2D grid, we can use simple Pythagoras
+ $distanceX = $to->getX()-$this->getX();
+ $distanceY = $to->getY()-$this->getY();
+
+ return pow(pow($distanceX, 2) + pow($distanceY, 2), 0.5);
+
+ }
 }

tests/OSRefTest.php

@@ -142,4 +142,15 @@ public function testGetters() {
  self::assertEquals(RefEll::airy1830(), $osRef->getRefEll());
  }
 
+ public function testDistance() {
+ //old OS HQ
+ $from = new OSRef(438700, 114800, 0, RefEll::airy1830());
+
+ //Tower of London
+ $to = new OSRef(533600, 180500, 0, RefEll::airy1830());
+
+ $distance = round($from->distance($to));
+ self::assertEquals(115423, $distance);
+ }
+
 }