Centroid calculation for alert distance

scwx-qt/source/scwx/qt/model/alert_model.cpp

@@ -48,6 +48,10 @@ public:
 
    GeographicLib::Geodesic geodesic_;
 
+   std::unordered_map<types::TextEventKey,
+                      common::Coordinate,
+                      types::TextEventHash<types::TextEventKey>>
+      centroidMap_;
    std::unordered_map<types::TextEventKey,
                       double,
                       types::TextEventHash<types::TextEventKey>>
@@ -173,30 +177,43 @@ void AlertModel::HandleAlert(const types::TextEventKey& alertKey)
 
    double distanceInMeters;
 
-   if (!p->textEventKeys_.contains(alertKey))
-   {
-      beginInsertRows(QModelIndex(), 0, 0);
+   // Get the most recent segment for the event
+   auto alertMessages =
+      manager::TextEventManager::Instance().message_list(alertKey);
+   std::shared_ptr<const awips::Segment> alertSegment =
+      alertMessages.back()->segments().back();
 
-      p->textEventKeys_.push_back(alertKey);
+   if (alertSegment->codedLocation_.has_value())
+   {
+      // Update centroid and distance
+      common::Coordinate centroid =
+         common::GetCentroid(alertSegment->codedLocation_->coordinates());
 
       p->geodesic_.Inverse(p->previousPosition_.latitude_,
                            p->previousPosition_.longitude_,
-                           0.0, // TODO: textEvent->latitude(),
-                           0.0, // TODO: textEvent->longitude(),
+                           centroid.latitude_,
+                           centroid.longitude_,
                            distanceInMeters);
 
-      p->distanceMap_[alertKey] = distanceInMeters;
+      p->centroidMap_.insert_or_assign(alertKey, centroid);
+      p->distanceMap_.insert_or_assign(alertKey, distanceInMeters);
+   }
+   else if (!p->centroidMap_.contains(alertKey))
+   {
+      // The alert has no location, so provide a default
+      p->centroidMap_.insert_or_assign(alertKey, common::Coordinate {0.0, 0.0});
+      p->distanceMap_.insert_or_assign(alertKey, 0.0);
+   }
 
+   // Update row
+   if (!p->textEventKeys_.contains(alertKey))
+   {
+      beginInsertRows(QModelIndex(), 0, 0);
+      p->textEventKeys_.push_back(alertKey);
       endInsertRows();
    }
    else
    {
-      p->geodesic_.Inverse(p->previousPosition_.latitude_,
-                           p->previousPosition_.longitude_,
-                           0.0, // TODO: textEvent->latitude(),
-                           0.0, // TODO: textEvent->longitude(),
-                           distanceInMeters);
-
       const int   row         = p->textEventKeys_.indexOf(alertKey);
       QModelIndex topLeft     = createIndex(row, kFirstColumn);
       QModelIndex bottomRight = createIndex(row, kLastColumn);
@@ -212,13 +229,18 @@ void AlertModel::HandleMapUpdate(double latitude, double longitude)
    double distanceInMeters;
 
    for (const auto& textEvent : p->textEventKeys_)
+   {
+      auto& centroid = p->centroidMap_.at(textEvent);
+
+      if (centroid != common::Coordinate {0.0, 0.0})
       {
          p->geodesic_.Inverse(latitude,
                               longitude,
-                           0.0, // TODO: textEvent->latitude(),
-                           0.0, // TODO: textEvent->longitude(),
+                              centroid.latitude_,
+                              centroid.longitude_,
                               distanceInMeters);
-      p->distanceMap_[textEvent] = distanceInMeters;
+         p->distanceMap_.insert_or_assign(textEvent, distanceInMeters);
+      }
    }
 
    p->previousPosition_ = {latitude, longitude};

wxdata/include/scwx/common/geographic.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <string>
+#include <vector>
 
 namespace scwx
 {
@@ -43,6 +44,16 @@ enum class DistanceType
    Miles
 };
 
+/**
+ * Calculate the geographic midpoint of a set of coordinates. Uses Method A
+ * described at http://www.geomidpoint.com/calculation.html.
+ *
+ * @param coordinates Set of unique coordinates
+ *
+ * @return Centroid
+ */
+Coordinate GetCentroid(const std::vector<Coordinate>& coordinates);
+
 std::string
 GetLatitudeString(double           latitude,
                   DegreeStringType type = DegreeStringType::Decimal);

wxdata/source/scwx/common/geographic.cpp

@@ -2,6 +2,7 @@
 #include <scwx/common/characters.hpp>
 
 #include <format>
+#include <numbers>
 
 namespace scwx
 {
@@ -12,6 +13,44 @@ static std::string GetDegreeString(double             degrees,
                                    DegreeStringType   type,
                                    const std::string& suffix);
 
+Coordinate GetCentroid(const std::vector<Coordinate>& coordinates)
+{
+   double x = 0.0;
+   double y = 0.0;
+   double z = 0.0;
+
+   for (const Coordinate& c : coordinates)
+   {
+      // Convert latitude and longitude to radians
+      double latitudeRadians  = c.latitude_ * std::numbers::pi / 180.0;
+      double longitudeRadians = c.longitude_ * std::numbers::pi / 180.0;
+
+      // Convert latitude and longitude to Cartesian coordinates
+      double x1 = std::cos(latitudeRadians) * std::cos(longitudeRadians);
+      double y1 = std::cos(latitudeRadians) * std::sin(longitudeRadians);
+      double z1 = std::sin(latitudeRadians);
+
+      // Combine with accumulators
+      x += x1;
+      y += y1;
+      z += z1;
+   }
+
+   // Compute averages
+   x /= coordinates.size();
+   y /= coordinates.size();
+   z /= coordinates.size();
+
+   // Convert Cartesian coordinates back to latitude and longitude
+   double hyp              = std::sqrt(x * x + y * y);
+   double latitudeRadians  = std::atan2(z, hyp);
+   double longitudeRadians = std::atan2(y, x);
+
+   // Return latitude and longitude in degrees
+   return {latitudeRadians * 180.0 / std::numbers::pi,
+           longitudeRadians * 180.0 / std::numbers::pi};
+}
+
 std::string GetLatitudeString(double latitude, DegreeStringType type)
 {
    std::string suffix {};