Add geographic-to-grid and grid-to-geographic projection methods in CoordinateConverter

- Introduced `toGrid` method enabling projection of geographic coordinates to grid coordinates with altitude source handling.
- Added `toCoordinate` method for inverse projection, converting grid coordinates back to geographic coordinates.
- Improved internal handling of altitude and ellipsoidal height for transformations.

src/main/java/dev/coph/flightscore/backend/map/CoordinateConverter.java

@@ -1,5 +1,9 @@
 package dev.coph.flightscore.backend.map;
 
+import dev.coph.flightscore.backend.competition.AltitudeSource;
+import dev.coph.flightscore.backend.coordinate.Altitude;
+import dev.coph.flightscore.backend.coordinate.Coordinate;
+
 /**
  * High precision conversion utility between any combination of {@link MapDatum}
  * and {@link MapGrid}.
@@ -32,7 +36,9 @@ package dev.coph.flightscore.backend.map;
 public final class CoordinateConverter {
 
     private static final double ARCSEC_TO_RAD = Math.PI / (180.0 * 3600.0);
-    /** Iteration tolerance for the Newton/fixed-point solvers (radians). */
+    /**
+     * Iteration tolerance for the Newton/fixed-point solvers (radians).
+     */
     private static final double TOLERANCE = 1.0e-14;
     private static final int MAX_ITERATIONS = 100;
 
@@ -47,11 +53,11 @@ public final class CoordinateConverter {
      * Converts a grid coordinate from one {@code (datum, grid)} combination into
      * any other {@code (datum, grid)} combination.
      *
-     * @param source       the coordinate in the source grid
+     * @param source      the coordinate in the source grid
-     * @param sourceDatum  datum the source coordinate is referenced to
+     * @param sourceDatum datum the source coordinate is referenced to
-     * @param sourceGrid   grid the source coordinate is projected with
+     * @param sourceGrid  grid the source coordinate is projected with
-     * @param targetDatum  datum the result shall be referenced to
+     * @param targetDatum datum the result shall be referenced to
-     * @param targetGrid   grid the result shall be projected with
+     * @param targetGrid  grid the result shall be projected with
      * @return the coordinate expressed in the target {@code (datum, grid)} combination
      */
     public static GridCoordinate convert(GridCoordinate source,
@@ -73,6 +79,36 @@ public final class CoordinateConverter {
         return toGrid(transformDatum(source, sourceDatum, targetDatum), targetDatum, targetGrid);
     }
 
+    /**
+     * Projects a {@link Coordinate} (referenced to {@code datum}) onto {@code grid}.
+     * <p>
+     * The {@link Coordinate#gpsAltitude() GPS altitude} is taken as the ellipsoidal
+     * height since it is the GNSS-derived height and therefore the closest match;
+     * the barometric altitude is used as a fallback and {@code 0} if neither is set.
+     */
+    public static GridCoordinate toGrid(Coordinate coordinate, AltitudeSource altitudeSource, MapDatum datum, MapGrid grid) {
+        return toGrid(toGeographicCoordinate(coordinate, altitudeSource), datum, grid);
+    }
+
+    /**
+     * Inverse projection of a grid coordinate onto a {@link Coordinate}. The
+     * resulting ellipsoidal height is stored as the coordinate's altitude.
+     */
+    public static Coordinate toCoordinate(GridCoordinate grid, MapDatum datum, MapGrid mapGrid) {
+        GeographicCoordinate geographic = toGeographic(grid, datum, mapGrid);
+        return new Coordinate(geographic.latitude(), geographic.longitude(),
+                Altitude.fromMeters(geographic.ellipsoidalHeight()));
+    }
+
+    private static GeographicCoordinate toGeographicCoordinate(Coordinate coordinate, AltitudeSource source) {
+        Altitude altitude = switch (source) {
+            case GPS -> coordinate.gpsAltitude();
+            case BAROMETRIC -> coordinate.barometricAltitude();
+        };
+        double height = altitude != null ? altitude.meters() : 0.0;
+        return new GeographicCoordinate(coordinate.latitude(), coordinate.longitude(), height);
+    }
+
     /**
      * Projects a geographic coordinate (referenced to {@code datum}) onto {@code grid}.
      */