SUPPORT:

1. be able to calculate the sat pos of BDS & Galileo
2. be able to Single postiting by GPS & Galileo

headers/select_epo.h

@@ -4,37 +4,55 @@
 #include<math.h>
 
 #include"public.h"
-
 /* -------------------------------------------------------------------------- */
-/// @brief 寻找与观测历元最近的卫星广播历元
-/// @param SecofWeek 计算得到的观测历元的周内秒
-/// @param sPRN 需要匹配的该历元卫星号
-/// @param nav_b 导航文件数据块结构体，与卫星号匹配
-/// @param satnum 广播星历卫星数量
-/// @param syscode 卫星系统代码，详情见PPUBLIC.H
-/// @return 返回最佳历元的绝对历元序号
+/// @brief find the nearest obs epoch with boardcast
+/// @param SecofWeek second of week of obs epoch time
+/// @param sPRN the satellite PRN which need to match
+/// @param nav_b nav data file structure
+/// @param satnum total number of boardcast satellite 
+/// @param syscode GNSS code, more on PPUBLIC.H
+/// @return Return the absolute epoch number of the best epoch 
+///			When there is no matching satellite number, the function returns -1
 /* -------------------------------------------------------------------------- */
 extern int select_epoch(double SecofWeek, int sPRN, pnav_body nav_b, int satnum, int syscode)
 {
-	int best_epoch = 0;
-	double min = 10000;//初始化最小值
+	int best_epoch = -1;
+	double min = 10000;//Initialize the minimum value
 	double Min;
-	if (syscode == GPS)
-	{
-		for (int i = 0; i < satnum; i++)
-		{
-			if (sPRN == nav_b[i].sPRN_GPS)
-			{
-				Min = fabs(SecofWeek - nav_b[i].TOE);
+	if (syscode == GPS)//Be judged as GPS
+	{	for (int i = 0; i < satnum; i++)
+		{	if (sPRN == nav_b[i].sPRN_GPS)
+			{	Min = fabs(SecofWeek - nav_b[i].TOE);
 				if (Min <= min)
 				{
 					best_epoch = i;
 					min = Min;
-				}
-			}
-		}
-	}
+				}}}
+		return best_epoch;}
+
+	if (syscode == BDS)//Be judged as BeiDou
+	{	for (int i = 0; i < satnum; i++)
+		{	if (sPRN == nav_b[i].sPRN_BDS)
+			{	Min = fabs(SecofWeek - nav_b[i].TOE);
+				if (Min <= min)
+				{
+					best_epoch = i;
+					min = Min;
+				}}}
+		return best_epoch;}
+
+	if (syscode == GAL)//Be judged as Galileo
+	{for (int i = 0; i < satnum; i++)
+		{	if (sPRN == nav_b[i].sPRN_GAL)
+			{	Min = fabs(SecofWeek - nav_b[i].TOE);
+				if (Min <= min)
+				{
+					best_epoch = i;
+					min = Min;
+				}}}
+		return best_epoch;}
+
 	return best_epoch;
 }
-
+/* --------------------------- END OF SELECT_EPO_H -------------------------- */
 #endif