Give heightsArrayFetchers responsibility to determine the needed tiles.

Demeton.Console/Wiring.fs

@@ -50,5 +50,7 @@ let fetchSrtmTile srtmDir localCacheDir : DemTileReader =
             writeTileToCache
         |> finalizeFetchSrtmTileProcessing
 
-let fetchSrtmHeights srtmDir localCacheDir =
-    fetchDemHeights (fetchSrtmTile srtmDir localCacheDir)
+let fetchSrtmHeights srtmDir localCacheDir srtmLevel lonLatBounds =
+    let tileReader = fetchSrtmTile srtmDir localCacheDir
+    let srtmTilesNeeded = boundsToTiles 3600 srtmLevel lonLatBounds
+    fetchDemHeights tileReader srtmTilesNeeded

Demeton.Tests/Aw3d/AW3D experiments.fs

@@ -45,7 +45,7 @@ let options: ShadeCommand.Options =
 
 
 // todo 10: move this to the command module?
-let fetchAw3dHeightsArray _ =
+let fetchAw3dHeightsArray _ _ =
     let tileDownloadingResult = ensureAw3dTiles CacheDir area
 
     match tileDownloadingResult with

Demeton.Tests/Commands tests/ShadeCommand/Generating shaded tile.fs

@@ -1,7 +1,6 @@
 module Tests.``Commands tests``.ShadeCommand.``Generating shaded tile``
 
-open Demeton.Dem.Types
-open Demeton.Dem.Funcs
+open Demeton.Geometry.Common
 open Raster
 open Demeton.Commands
 open Demeton.Shaders
@@ -27,23 +26,27 @@ let mockRasterShader _ _ _ _ _ _ = ()
 let rootShadingStep = Pipeline.Common.CustomShading "some shader"
 
 [<Fact>]
-let ``Tile generator correctly calculates which SRTM tiles it needs`` () =
+let ``Tile generator correctly specifies DEM level and bounds for tile downloaders``
+    ()
+    =
 
-    let correctSrtmTilesWereRequested (tiles: DemTileId seq) =
-        let tilesArray = tiles |> Seq.toArray
+    let correctLevelAndAreaWereProvided level area =
+        test <@ level = srtmLevel @>
 
         test
             <@
-                tilesArray = [| demTileId 4 0 -4
-                                demTileId 4 1 -4
-                                demTileId 4 0 -3
-                                demTileId 4 1 -3 |]
+                // todo 0: update the expectation
+                area = { MinLon = 0
+                         MinLat = 0
+                         MaxLon = 20
+                         MaxLat = 30 }
             @>
 
         heights |> Some |> Ok
 
+    // todo 0: looks like the correctLevelAndAreaWereProvided is never called
     ShadeCommand.generateShadedRasterTile
-        [| correctSrtmTilesWereRequested |]
+        [| correctLevelAndAreaWereProvided |]
         (fun _ -> mockRasterShader)
         srtmLevel
         tileRect
@@ -57,7 +60,7 @@ let ``When heights array fetcher returns None, tile generator does nothing and r
     ()
     =
 
-    let returnNoneForHeightsArray _ = Ok None
+    let returnNoneForHeightsArray _ _ = Ok None
 
     let shadeTileResult =
         ShadeCommand.generateShadedRasterTile
@@ -76,7 +79,7 @@ let ``When heights array fetcher returns an error, tile generator returns an err
     ()
     =
 
-    let returnErrorInsteadOfHeightsArray _ = Error "something is wrong"
+    let returnErrorInsteadOfHeightsArray _ _ = Error "something is wrong"
 
     let shadeTileResult =
         ShadeCommand.generateShadedRasterTile
@@ -91,7 +94,7 @@ let ``When heights array fetcher returns an error, tile generator returns an err
 
 [<Fact>]
 let ``Tile generator prepares the tile image data and returns it`` () =
-    let fetchSomeHeights _ = heights |> Some |> Ok
+    let fetchSomeHeights _ _ = heights |> Some |> Ok
 
     let mutable imageDataReceived = None
 

Demeton.Tests/WorldCover/WorldCover experiments.fs

@@ -85,7 +85,9 @@ let ``Render hillshading with WorldCover water bodies`` () =
         // raster available (it's too big to be added to git repo)
         ()
     else
-        let worldCoverTileId = demTileXYId -6 -45
+        let worldCoverTilesNeeded = boundsToWorldCoverTiles area
+
+        let worldCoverTileId = demTileXYId 6 -45
 
         let cacheDir = "cache"
 
@@ -112,7 +114,7 @@ let ``Render hillshading with WorldCover water bodies`` () =
             |> outlineWaterBodies waterBodiesHeightsArray
             |> Seq.toList
 
-        let fetchWorldCoverHeightsArray tileIds =
+        let fetchWorldCoverHeightsArray level area =
             waterBodiesHeightsArray |> Some |> Result.Ok
 
         let heightsArraysFetchers =

Demeton/Commands/ShadeCommand.fs

@@ -4,7 +4,6 @@ module Demeton.Commands.ShadeCommand
 open CommandLine
 open CommandLine.Common
 open Demeton.Dem.Types
-open Demeton.Dem.Funcs
 open Raster
 open Demeton.Geometry
 open Demeton.Geometry.Common
@@ -467,14 +466,9 @@ let generateShadedRasterTile
               MaxLon = radToDeg (max lon1Rad lon2Rad)
               MaxLat = radToDeg (max lat1Rad lat2Rad) }
 
-        // todo 15: the needed tiles calculation has to be generalized so we
-        //   could also load non-SRTM tiles. We should probably move the
-        //   responsibility to the tile downloader itself, giving it lonLatBounds.
-        let srtmTilesNeeded = boundsToTiles 3600 srtmLevel lonLatBounds
-
         let fetchingResults =
             heightsArrayFetchers
-            |> Array.map (fun fetcher -> fetcher srtmTilesNeeded)
+            |> Array.map (fun fetcher -> fetcher srtmLevel lonLatBounds)
 
         let firstErrorMaybe = fetchingResults |> Array.tryFind Result.isError
 

Demeton/Commands/TileShadeCommand.fs

@@ -356,12 +356,7 @@ let calculateGeoAreaMbr options projection =
         Result.Error "Some of the tile bounding points could not be projected."
 
 
-let fetchAw3dHeightsArray
-    mapProjection
-    cacheDir
-    coverageArea
-    (tilesIds: DemTileId seq)
-    =
+let fetchAw3dHeightsArray mapProjection cacheDir demLevel coverageArea =
     let coveragePoints =
         [ (coverageArea.MinLon, coverageArea.MinLat)
           (coverageArea.MaxLon, coverageArea.MaxLat) ]
@@ -497,7 +492,7 @@ let run (options: Options) : Result<unit, string> =
         match calculateGeoAreaMbr options mapProjection with
         | Ok coverageArea ->
             ShadeCommand.generateShadedRasterTile
-                [| fetchAw3dHeightsArray mapProjection cacheDir coverageArea |]
+                [| fetchAw3dHeightsArray mapProjection cacheDir |]
                 createShadingFuncById
                 srtmLevel
                 tileRect

Demeton/Dem/Funcs.fs

@@ -412,36 +412,37 @@ let extract
 /// Provides a function to fetch a heights array from a sequence of DEM tiles,
 /// using a specified DEM tile reader.
 /// </summary>
-let fetchDemHeights (readDemTile: DemTileReader) : DemHeightsArrayFetcher =
-    fun tilesToUse ->
-
-        let mutable errorMessage = None
-        let mutable i = 0
-
-        let tilesArray = tilesToUse |> Seq.toArray
-        let mutable heightsArraysToMerge = []
-
-        while i < tilesArray.Length && Option.isNone errorMessage do
-            let tileCoords = tilesArray.[i]
-            let tileLoadResult = readDemTile tileCoords
-
-            match tileLoadResult with
-            | Ok(Some heightsArray) ->
-                heightsArraysToMerge <- heightsArray :: heightsArraysToMerge
-                ()
-            | Error message ->
-                errorMessage <- Some message
-                ()
-            | _ -> ()
-
-            i <- i + 1
-
-        match errorMessage with
-        | Some error -> Error error
-        | _ ->
-            let mergedRect = heightsArraysToMerge |> mbrOfHeightsArrays
+let fetchDemHeights
+    (readDemTile: DemTileReader)
+    (tilesToUse: DemTileId seq)
+    : HeightsArrayMaybeResult =
+    let mutable errorMessage = None
+    let mutable i = 0
+
+    let tilesArray = tilesToUse |> Seq.toArray
+    let mutable heightsArraysToMerge = []
+
+    while i < tilesArray.Length && Option.isNone errorMessage do
+        let tileCoords = tilesArray.[i]
+        let tileLoadResult = readDemTile tileCoords
+
+        match tileLoadResult with
+        | Ok(Some heightsArray) ->
+            heightsArraysToMerge <- heightsArray :: heightsArraysToMerge
+            ()
+        | Error message ->
+            errorMessage <- Some message
+            ()
+        | _ -> ()
+
+        i <- i + 1
+
+    match errorMessage with
+    | Some error -> Error error
+    | _ ->
+        let mergedRect = heightsArraysToMerge |> mbrOfHeightsArrays
 
-            Ok(merge mergedRect heightsArraysToMerge)
+        Ok(merge mergedRect heightsArraysToMerge)
 
 
 

Demeton/Dem/Types.fs

@@ -1,6 +1,7 @@
 module Demeton.Dem.Types
 
 open System
+open Demeton.Geometry.Common
 open Raster
 
 type DemHeight = int16
@@ -290,6 +291,8 @@ type DemTileName = string
 
 
 /// <summary>
-/// A function that fetches a heights array from a sequence of DEM tiles.
+/// A function that fetches a heights array from a sequence of DEM tiles
+/// needed to cover the specified area using DEM tiles of the specified level.
 /// </summary>
-type DemHeightsArrayFetcher = DemTileId seq -> HeightsArrayMaybeResult
+type DemHeightsArrayFetcher =
+    DemLevel -> LonLatBounds -> HeightsArrayMaybeResult