Implement bilinear interpolation

linear-interpolation/src/interpolate.cpp

@@ -0,0 +1,43 @@
+#include <cmath>
+
+#include <ranges>
+#include "interpolate.h"
+
+using namespace std;
+
+// Inspired by https://numerical.recipes/book.html Chapter 3.6
+point bilinearInterpolate(const UVGrid &uvGrid, std::tuple<int, double, double> timeLatLon) {
+    auto [time, lat, lon] = timeLatLon;
+
+    double latStep = uvGrid.latStep();
+    double lonStep = uvGrid.lonStep();
+    int timeStep = uvGrid.timeStep();
+
+    int latIndex = (lat-uvGrid.lats[0])/latStep;
+    int lonIndex = (lon-uvGrid.lons[0])/lonStep;
+    int timeIndex = (time-uvGrid.times[0])/timeStep;
+
+    double timeRatio = (static_cast<double>(time)-uvGrid.times[timeIndex])/timeStep;
+    double latRatio = (lat-uvGrid.lats[latIndex]) / latStep;
+    double lonRatio = (lon-uvGrid.lons[lonIndex]) / lonStep;
+
+    point point = {0, 0};
+    for(int time = 0; time <= 1; time++) {
+        for(int lat = 0; lat <= 1; lat++) {
+            for(int lon = 0; lon <= 1; lon++) {
+                auto vertex = uvGrid.uvMatrix[
+                        timeIndex + time < uvGrid.uvMatrix.extent(0) ? timeIndex + 1 : timeIndex,
+                        latIndex + lat < uvGrid.uvMatrix.extent(1) ? latIndex + 1 : latIndex,
+                        lonIndex + lon < uvGrid.uvMatrix.extent(2) ? lonIndex + 1 : lonIndex
+                ];
+
+                double timeRation = (1 - time)*(1-timeRatio) + time*timeRatio;
+                double latRation = (1 - lat)*(1-latRatio) + lat*latRatio;
+                double lonRation = (1 - lon)*(1-lonRatio) + lon*lonRatio;
+                point += timeRation * latRation * lonRation * vertex;
+            }
+        }
+    }
+
+    return point;
+}