Index: trunk/ippTools/src/difftool.c
===================================================================
--- trunk/ippTools/src/difftool.c	(revision 23633)
+++ trunk/ippTools/src/difftool.c	(revision 23634)
@@ -1274,4 +1274,7 @@
                    "ABS(TIME_TO_SEC(TIMEDIFF(inputRawExp.dateobs, templateRawExp.dateobs)))", "<=");
     PXOPT_COPY_F32(config->args, selectWhere, "-rotdiff", "ABS(inputRawExp.posang - templateRawExp.posang)", "<=");
+    // Haversine formula for great circle distance
+    PXOPT_COPY_F32(config->args, selectWhere, "-distance",
+                   "DEGREES(2*ASIN(SQRT(POW(SIN(inputRawExp.decl - templateRawExp.decl),2) + COS(inputRawExp.decl)*COS(templateRawExp.decl)*POW(SIN(inputRawExp.ra - templateRawExp.ra),2))))", "<=");
 
     // Restrictions for inserting skycells