linstring approach. still fragmented

water.py

@@ -3,9 +3,143 @@ import argparse
 import pandas as pd
 import geopandas as gpd
 import geohash
+import numpy as np
 import logging
-from shapely.geometry import box
-from shapely.ops import unary_union
+from shapely.geometry import box, LineString, MultiLineString, Point
+from shapely.ops import unary_union, linemerge, split
+import matplotlib.pyplot as plt
+
+def split_polygon_by_coastline(tile_polygon, coastline):
+    """
+    Splits the geohash tile polygon into two by the coastline and keeps the polygon on the 'right' side
+    based on the LineString's direction.
+    
+    Parameters:
+        - tile_polygon: The full geohash bounding box as a Polygon.
+        - coastline: The merged LineString coastline within the tile.
+    
+    Returns:
+        - The remaining water polygon after removing the 'left' side.
+    """
+    if coastline.is_empty or coastline.geom_type not in ["LineString", "MultiLineString"]:
+        return None  # No valid coastline
+
+    # Convert MultiLineString to the longest single LineString if necessary
+    if coastline.geom_type == "MultiLineString":
+        coastline = max(coastline.geoms, key=lambda g: g.length)
+
+    # Get the midpoint of the LineString
+    midpoint = coastline.interpolate(0.5, normalized=True)
+
+    # Compute the direction of the coastline (from first to last point)
+    coords = np.array(coastline.coords)
+    start, end = coords[0], coords[-1]
+    dx, dy = end[0] - start[0], end[1] - start[1]
+
+    # Compute normal vector (perpendicular to the coastline direction)
+    normal = np.array([-dy, dx])  # Rotate 90° counterclockwise
+    normal = normal / np.linalg.norm(normal)  # Normalize
+
+    # Compute a test point on the 'right' side
+    test_point = midpoint.x + normal[0], midpoint.y + normal[1]
+
+    # Perform the split
+    split_result = split(tile_polygon, coastline)
+
+    if not split_result or len(split_result.geoms) < 2:
+        return None  # No valid split
+
+    # Choose the polygon that contains the test point
+    for poly in split_result.geoms:
+        if poly.contains(Point(test_point)):
+            return poly  # Keep the 'right' side
+
+    return None  # Fail-safe
+
+
+def group_continuous_coastline(segments, gap_threshold=0.001):
+    """
+    Groups and merges only those LineStrings that are properly connected to each other.
+    Separate coastlines remain unmerged (e.g., islands).
+    
+    Parameters:
+        - segments: List of LineStrings.
+        - gap_threshold: Max distance (degrees) between segment endpoints to be considered connected.
+    
+    Returns:
+        - List of merged continuous LineStrings.
+    """
+    connected_groups = []
+    remaining_segments = list(segments)
+
+    while remaining_segments:
+        # Start a new group with one segment
+        group = [remaining_segments.pop(0)]
+
+        added = True
+        while added:
+            added = False
+            for seg in remaining_segments[:]:
+                if is_connected_to_group(seg, group, gap_threshold):
+                    group.append(seg)
+                    remaining_segments.remove(seg)
+                    added = True  # Continue expanding the group
+
+        # Merge each connected group separately
+        if len(group) > 1:
+            merged = linemerge(MultiLineString(group))
+        else:
+            merged = group[0]
+
+        connected_groups.append(merged)
+
+    return connected_groups
+
+
+def is_connected_to_group(line, group, gap_threshold=0.001):
+    """
+    Checks if a LineString is connected to any other in a group.
+    A connection means they share an endpoint within a small gap threshold.
+    """
+    line_start, line_end = Point(line.coords[0]), Point(line.coords[-1])
+
+    for other in group:
+        other_start, other_end = Point(other.coords[0]), Point(other.coords[-1])
+        if (
+            line_start.distance(other_end) < gap_threshold or
+            line_end.distance(other_start) < gap_threshold
+        ):
+            return True  # They are connected within the gap threshold
+
+    return False
+
+def plot_coastline_segments(geohash_code, fragmented_coastline, output_folder="debug_plots"):
+    """Saves a PNG plot of coastline segments for debugging."""
+    os.makedirs(output_folder, exist_ok=True)  # Ensure the output folder exists
+    output_file = os.path.join(output_folder, f"{geohash_code}.png")
+
+    fig, ax = plt.subplots(figsize=(6, 6))
+    colors = ['red', 'blue', 'green', 'purple', 'orange', 'cyan']
+
+    # Convert to list if MultiLineString
+    if fragmented_coastline.geom_type == "MultiLineString":
+        segments = list(fragmented_coastline.geoms)
+    else:
+        segments = [fragmented_coastline]
+
+    for idx, segment in enumerate(segments):
+        x, y = segment.xy
+        ax.plot(x, y, color=colors[idx % len(colors)], linewidth=2, label=f"Segment {idx+1}")
+
+    ax.set_title(f"Coastline Segments in {geohash_code}")
+    ax.set_xlabel("Longitude")
+    ax.set_ylabel("Latitude")
+    ax.legend()
+    
+    plt.savefig(output_file, dpi=300, bbox_inches="tight")  # Save as PNG
+    plt.close(fig)  # Close the plot to free memory
+
+    print(f"✅ Saved coastline debug plot: {output_file}")
 
 # Configure logging
 logging.basicConfig(format="%(levelname)s: %(message)s", level=logging.INFO)
@@ -33,8 +167,48 @@ def ensure_crs_consistency(gdf):
         gdf = gdf.to_crs("EPSG:4326")
     return gdf
 
+def check_coastline_continuity(coastline_gdf, geohash_code):
+    """Checks if the coastline forms a continuous LineString and attempts to merge fragmented parts."""
+    if coastline_gdf.empty:
+        logger.warning(f"Geohash {geohash_code}: No coastline to check.")
+        return False
+
+    # Convert to a list of valid LineStrings
+    coastline_list = [geom for geom in coastline_gdf.geometry if geom and geom.geom_type in ["LineString", "MultiLineString"]]
+
+    if not coastline_list:
+        logger.error(f"Geohash {geohash_code}: No valid LineString geometries found.")
+        return False
+
+    # Merge the coastline segments (ensuring not empty)
+    merged_coastlines = group_continuous_coastline(coastline_list)
+
+    if not merged_coastlines:
+        logger.error(f"Geohash {geohash_code}: Merging failed. No valid coastlines found.")
+        merged_coastline = MultiLineString([])  # Return an empty MultiLineString
+    else:
+        merged_coastline = max(merged_coastlines, key=lambda ls: ls.length)
+
+    # Ensure the result is valid
+    if merged_coastline.is_empty:
+        logger.error(f"Geohash {geohash_code}: Merged coastline is empty.")
+        return False
+
+    if isinstance(merged_coastline, LineString):
+        logger.info(f"Geohash {geohash_code}: Coastline is continuous.")
+        plot_coastline_segments(geohash_code, merged_coastline)
+        return True
+
+    if isinstance(merged_coastline, MultiLineString):
+        logger.warning(f"Geohash {geohash_code}: Coastline remains fragmented ({len(merged_coastline.geoms)} parts).")
+        plot_coastline_segments(geohash_code, merged_coastline)
+        return False
+
+    logger.error(f"Geohash {geohash_code}: Unexpected coastline geometry ({merged_coastline.geom_type}).")
+    return False
+
 def process_geohash_files(coastline_gdf, geohash_files):
-    """Processes each geohash file: removes old coastlines and inserts updated ones."""
+    """Processes each geohash file: updates coastline and adds water polygons."""
     for geohash_code, file_path in geohash_files.items():
         logger.info(f"Processing {file_path}...")
 
@@ -55,29 +229,46 @@ def process_geohash_files(coastline_gdf, geohash_files):
         bbox = geohash_bbox(geohash_code)
         new_coastline = coastline_gdf[coastline_gdf.intersects(bbox)].copy()
 
-        # Clip coastline to the geohash boundary
-        new_coastline["geometry"] = new_coastline["geometry"].apply(lambda geom: geom.intersection(bbox))
-
         if new_coastline.empty:
-            logger.info(f"No coastline found for {geohash_code}. Skipping update.")
+            logger.info(f"No coastline found for {geohash_code}. Skipping coastline update.")
             continue
 
-        # Assign "natural: coastline" tag
-        new_coastline["tags"] = [{"natural": "coastline"}] * len(new_coastline)
+        # Merge continuous coastline segments
+        merged_coastlines = group_continuous_coastline(new_coastline.geometry)
+        if merged_coastlines:
+            merged_coastline = max(merged_coastlines, key=lambda ls: ls.length)  # Pick the longest coastline
+        else:
+            merged_coastline = None
 
-        # Ensure columns match before merging
-        for col in ["feature_id", "tags"]:
-            if col not in filtered_gdf.columns:
-                filtered_gdf[col] = None
-            if col not in new_coastline.columns:
-                new_coastline[col] = None
+        if merged_coastline is None:
+            logger.warning(f"Geohash {geohash_code}: Coastline merging failed.")
+            continue
 
-        # Merge updated coastline into geohash file
+        logger.info(f"Adding water polygon for {geohash_code}...")
+
+        # Create a full water polygon covering the entire geohash tile
+        tile_polygon = bbox
+
+        # Split the tile polygon using the coastline
+        water_polygon = split_polygon_by_coastline(tile_polygon, merged_coastline)
+
+        if water_polygon:
+            # Assign water tags
+            water_gdf = gpd.GeoDataFrame(
+                {"geometry": [water_polygon], "tags": [{"natural": "water", "water": "sea"}]},
+                crs="EPSG:4326"
+            )
+
+            # Append the water polygon to the updated geohash file
+            updated_gdf = gpd.GeoDataFrame(pd.concat([filtered_gdf, new_coastline, water_gdf], ignore_index=True), crs="EPSG:4326")
+            logger.info(f"Water polygon added for {geohash_code}.")
+        else:
+            logger.warning(f"Could not split water polygon for {geohash_code}. Skipping water addition.")
             updated_gdf = gpd.GeoDataFrame(pd.concat([filtered_gdf, new_coastline], ignore_index=True), crs="EPSG:4326")
 
         # Save back to parquet
         updated_gdf.to_parquet(file_path, index=False)
-        logger.info(f"Updated coastline in {file_path}")
+        logger.info(f"Updated geohash file {file_path}.")
 
 def main():
     parser = argparse.ArgumentParser(description="Update coastline geometries in existing geohash parquet files.")