[PATCH v2] Simplify distance calculations

[Anton Lundin]

This simplifies the distance calculations and removes a dependency.

This version uses propper math instead of my to simple previous version.

Signed-off-by: Anton Lundin <glance at acc.umu.se>
---
 CMakeLists.txt  |  4 ++--
 divesite.c      | 23 +++++++++++++++++++----
 qt-ui/globe.cpp |  8 --------
 units.h         |  5 +++++
 4 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0125b89..f5322b8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -132,8 +132,8 @@ if(NOT (insource OR insourcedir))
 endif()
 
 # configure Qt.
-find_package(Qt5 REQUIRED COMPONENTS Core Concurrent Widgets Network WebKitWidgets PrintSupport Svg Test LinguistTools Positioning)
-set(QT_LIBRARIES Qt5::Core Qt5::Concurrent Qt5::Widgets Qt5::Network Qt5::WebKitWidgets Qt5::PrintSupport Qt5::Svg Qt5::Positioning)
+find_package(Qt5 REQUIRED COMPONENTS Core Concurrent Widgets Network WebKitWidgets PrintSupport Svg Test LinguistTools)
+set(QT_LIBRARIES Qt5::Core Qt5::Concurrent Qt5::Widgets Qt5::Network Qt5::WebKitWidgets Qt5::PrintSupport Qt5::Svg)
 set(QT_TEST_LIBRARIES ${QT_LIBRARIES} Qt5::Test)
 
 # Generate the ssrf-config.h every 'make'
diff --git a/divesite.c b/divesite.c
index 3caa7b3..e096c71 100644
--- a/divesite.c
+++ b/divesite.c
@@ -2,6 +2,8 @@
 #include "divesite.h"
 #include "dive.h"
 
+#include <math.h>
+
 struct dive_site_table dive_site_table;
 
 /* there could be multiple sites of the same name - return the first one */
@@ -34,8 +36,21 @@ uint32_t get_dive_site_uuid_by_gps(degrees_t latitude, degrees_t longitude, stru
 	return 0;
 }
 
-/* this is in globe.cpp, so including the .h file is a pain */
-extern double getDistance(int lat1, int lon1, int lat2, int lon2);
+// Calculate the distance in meters between two coordinates.
+static unsigned int get_distance(degrees_t lat1, degrees_t lon1, degrees_t lat2, degrees_t lon2)
+{
+	double lat1_r = udeg_to_radians(lat1.udeg);
+	double lat2_r = udeg_to_radians(lat2.udeg);
+	double lat_d_r = udeg_to_radians(lat2.udeg-lat1.udeg);
+	double lon_d_r = udeg_to_radians(lon2.udeg-lon1.udeg);
+
+	double a = sin(lat_d_r/2) * sin(lat_d_r/2) +
+		cos(lat2_r) * cos(lat2_r) * sin(lon_d_r/2) * sin(lon_d_r/2);
+	double c = 2 * atan2(sqrt(a), sqrt(1.0 - a));
+
+	// Earth radious in metres
+	return 6371000 * c;
+}
 
 /* find the closest one, no more than distance meters away - if more than one at same distance, pick the first */
 uint32_t get_dive_site_uuid_by_gps_proximity(degrees_t latitude, degrees_t longitude, int distance, struct dive_site **dsp)
@@ -43,10 +58,10 @@ uint32_t get_dive_site_uuid_by_gps_proximity(degrees_t latitude, degrees_t longi
 	int i;
 	int uuid = 0;
 	struct dive_site *ds;
-	double cur_distance, min_distance = distance + 0.001;
+	unsigned int cur_distance, min_distance = distance;
 	for_each_dive_site (i, ds) {
 		if (dive_site_has_gps_location(ds) &&
-		    (cur_distance = getDistance(ds->latitude.udeg, ds->longitude.udeg, latitude.udeg, longitude.udeg)) < min_distance) {
+		    (cur_distance = get_distance(ds->latitude, ds->longitude, latitude, longitude)) < min_distance) {
 			min_distance = cur_distance;
 			uuid = ds->uuid;
 			if (dsp)
diff --git a/qt-ui/globe.cpp b/qt-ui/globe.cpp
index 76d48b7..b8e0ec8 100644
--- a/qt-ui/globe.cpp
+++ b/qt-ui/globe.cpp
@@ -1,5 +1,4 @@
 #include "globe.h"
-#include <QGeoCoordinate>
 #ifndef NO_MARBLE
 #include "mainwindow.h"
 #include "helpers.h"
@@ -393,10 +392,3 @@ void GlobeGPS::reload()
 {
 }
 #endif
-
-extern "C" double getDistance(int lat1, int lon1, int lat2, int lon2)
-{
-	QGeoCoordinate c1(lat1 / 1000000.0, lon1 / 1000000.0);
-	QGeoCoordinate c2(lat2 / 1000000.0, lon2 / 1000000.0);
-	return c1.distanceTo(c2);
-}
diff --git a/units.h b/units.h
index 90d7949..0baf2ff 100644
--- a/units.h
+++ b/units.h
@@ -119,6 +119,11 @@ typedef struct
 	int udeg;
 } degrees_t;
 
+static inline double udeg_to_radians(int udeg)
+{
+	return (udeg * M_PI) / (1000000.0 * 180.0);
+}
+
 static inline double grams_to_lbs(int grams)
 {
 	return grams / 453.6;
-- 
2.1.4