create backend

lib/mound_hunters/ohio_lidar.ex

@@ -0,0 +1,196 @@
+defmodule MoundHunters.OhioLidar do
+  @moduledoc """
+  Functions for querying Ohio's ArcGIS tile service and coordinate conversions.
+  """
+  require Logger
+
+  # Ohio ArcGIS tile service
+  @tile_service_url "https://maps.ohio.gov/arcgis/rest/services/OGRIP/3DepTiles/MapServer/0/query"
+
+  # OGRIP download URL template
+  @download_url_template "https://gis1.oit.ohio.gov/ZIPARCHIVES_III/ELEVATION/3DEP/LIDAR/{county}/{tile_name}.zip"
+
+  @doc """
+  Convert lon/lat (WGS84) to Web Mercator (EPSG:3857).
+  
+  Formula from: https://en.wikipedia.org/wiki/Web_Mercator_projection
+  """
+  def lonlat_to_webmercator(lon, lat) do
+    # Earth radius in meters
+    r = 6378137.0
+
+    # Convert to radians
+    lon_rad = lon * :math.pi() / 180.0
+    lat_rad = lat * :math.pi() / 180.0
+
+    # Web Mercator formulas
+    x = r * lon_rad
+    y = r * :math.log(:math.tan(:math.pi() / 4.0 + lat_rad / 2.0))
+
+    {x, y}
+  end
+
+  @doc """
+  Query Ohio ArcGIS service for tile information at given coordinates.
+  
+  Returns {:ok, tile_info} or {:error, reason}
+  
+  tile_info contains: %{
+    tile_name: "BS19820747",
+    county: "LIC",
+    year: "2020",
+    block: "4",
+    note: "..."
+  }
+  """
+  def query_tile_info(lon, lat) do
+    {x, y} = lonlat_to_webmercator(lon, lat)
+
+    geometry =
+      Jason.encode!(%{
+        x: x,
+        y: y,
+        spatialReference: %{wkid: 3857}
+      })
+
+    params = %{
+      "f" => "json",
+      "returnGeometry" => "false",
+      "spatialRel" => "esriSpatialRelIntersects",
+      "geometry" => geometry,
+      "geometryType" => "esriGeometryPoint",
+      "inSR" => "3857",
+      "outFields" => "*",
+      "outSR" => "3857"
+    }
+
+    Logger.debug("Querying ArcGIS for tile at (#{lon}, #{lat}) -> WebMercator (#{x}, #{y})")
+
+    case HTTPoison.get(@tile_service_url, [], params: params, timeout: 10_000) do
+      {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->
+        parse_tile_response(body)
+
+      {:ok, %HTTPoison.Response{status_code: status}} ->
+        Logger.error("ArcGIS returned status #{status}")
+        {:error, "ArcGIS service returned status #{status}"}
+
+      {:error, %HTTPoison.Error{reason: reason}} ->
+        Logger.error("Failed to query ArcGIS: #{inspect(reason)}")
+        {:error, "Network error: #{inspect(reason)}"}
+    end
+  end
+
+  defp parse_tile_response(body) do
+    case Jason.decode(body) do
+      {:ok, %{"features" => []}} ->
+        {:error, :no_tile_found}
+
+      {:ok, %{"features" => [feature | _]}} ->
+        attrs = feature["attributes"]
+
+        tile_info = %{
+          tile_name: attrs["TileName"],
+          county: attrs["County"],
+          year: attrs["Year"],
+          block: attrs["Block"],
+          note: attrs["note"]
+        }
+
+        {:ok, tile_info}
+
+      {:ok, _} ->
+        {:error, :invalid_response}
+
+      {:error, _} ->
+        {:error, :json_parse_error}
+    end
+  end
+
+  @doc """
+  Get the download URL for a tile.
+  """
+  def get_download_url(tile_name, county) do
+    @download_url_template
+    |> String.replace("{county}", county)
+    |> String.replace("{tile_name}", tile_name)
+  end
+
+  @doc """
+  Download a tile ZIP file from OGRIP.
+  
+  Returns {:ok, file_path} or {:error, reason}
+  """
+  def download_tile(tile_name, county, output_path) do
+    url = get_download_url(tile_name, county)
+    Logger.info("Downloading #{tile_name} from #{url}")
+
+    # Ensure output directory exists
+    output_path
+    |> Path.dirname()
+    |> File.mkdir_p!()
+
+    case HTTPoison.get(url, [], timeout: 60_000, recv_timeout: 60_000, stream_to: self()) do
+      {:ok, %HTTPoison.AsyncResponse{id: id}} ->
+        receive_download(id, output_path, 0)
+
+      {:error, %HTTPoison.Error{reason: reason}} ->
+        Logger.error("Failed to start download: #{inspect(reason)}")
+        {:error, "Download failed: #{inspect(reason)}"}
+    end
+  end
+
+  defp receive_download(id, output_path, bytes_received) do
+    receive do
+      %HTTPoison.AsyncStatus{id: ^id, code: 200} ->
+        Logger.debug("Download started, status 200")
+        receive_download(id, output_path, bytes_received)
+
+      %HTTPoison.AsyncStatus{id: ^id, code: status} ->
+        Logger.error("Download failed with status #{status}")
+        {:error, "HTTP status #{status}"}
+
+      %HTTPoison.AsyncHeaders{id: ^id} ->
+        # Start writing to file
+        File.open(output_path, [:write, :binary], fn file ->
+          receive_download_chunks(id, file, bytes_received)
+        end)
+
+      %HTTPoison.AsyncEnd{id: ^id} ->
+        Logger.error("Download ended prematurely")
+        {:error, :unexpected_end}
+
+      {:error, reason} ->
+        Logger.error("Download error: #{inspect(reason)}")
+        {:error, reason}
+    after
+      70_000 ->
+        {:error, :timeout}
+    end
+  end
+
+  defp receive_download_chunks(id, file, bytes_received) do
+    receive do
+      %HTTPoison.AsyncChunk{id: ^id, chunk: chunk} ->
+        IO.binwrite(file, chunk)
+        new_bytes = bytes_received + byte_size(chunk)
+
+        # Log progress every 10MB
+        if div(new_bytes, 10_485_760) > div(bytes_received, 10_485_760) do
+          Logger.debug("Downloaded #{div(new_bytes, 1_048_576)} MB")
+        end
+
+        receive_download_chunks(id, file, new_bytes)
+
+      %HTTPoison.AsyncEnd{id: ^id} ->
+        size_mb = bytes_received / 1_048_576
+        Logger.info("Download complete: #{Float.round(size_mb, 2)} MB")
+        {:ok, bytes_received}
+
+      {:error, reason} ->
+        {:error, reason}
+    after
+      70_000 ->
+        {:error, :timeout}
+    end
+  end
+end