...

cxx/mcc_mount_pz.h

@@ -200,6 +200,39 @@ public:
         }
     }
 
+    // compute intersection point for the case of sideral-like moving
+    bool intersectPoint(traits::mcc_celestial_point_c auto const& target, traits::mcc_celestial_point_c auto& int_point)
+    {
+        coord_t ha, dec, az;
+
+        _coord2coord(target.coordPairKind, target.x, target.y, target.time_point,
+                     MccCoordPairKind::COORDS_KIND_HADEC_APP, ha, dec);
+
+        // compute HA for intersection point
+        double cos_ha =
+            (std::sin(_altLimit) - std::sin(dec) * std::sin(_latitude)) / std::cos(dec) / std::cos(_latitude);
+
+        if (cos_ha > 1.0) {  // no intersection
+            // compute culmination points?
+            return false;
+        }
+
+        double cosA = -sin(dec) * std::cos(_latitude) + std::cos(dec) * std::sin(_latitude) * cos_ha;
+        cosA /= std::cos(_altLimit);
+
+        if constexpr (KIND ==
+                      MccAltLimitKind::MIN_ALT_LIMIT) {  // the closest time point is one after upper culmination
+            az = std::acos(cosA);
+        } else if constexpr (KIND == MccAltLimitKind::MAX_ALT_LIMIT) {  // the closest time point is one before upper
+                                                                        // culmination
+            az = -std::acos(cosA);
+        }
+
+        _coord2coord(MccCoordPairKind::COORDS_KIND_AZALT, az, _altLimit, target.time_point, int_point.coordPairKind,
+                     int_point.x, int_point.y);
+
+        return true;
+    }
 
 private:
     coord_t _altLimit, _latitude, _abs_lat, _lat_lim;
@@ -274,13 +307,14 @@ private:
         }
 
         double ha;
+        // WARNING: what about south hemisphere?!!!
         if (before_upper_culm) {
             ha = -std::acos(cos_ha);  // HA before upper culmination
         } else {
             ha = std::acos(cos_ha);  // HA after upper culmination!!
         }
 
-        MccAngle time_ang = ha - ha_app;  // in sideral time scale
+        coord_t time_ang = ha - ha_app;  // in sideral time scale
 
         if (time_ang < 0.0) {  // next day
             time_ang += pi2;