Improve compatibility and generation

Obj2Tiles/Options.cs

@@ -42,7 +42,7 @@ public sealed class Options
     [Option("scale", Required = false, HelpText = "Scale for data if using units other than meters ( 1200.0/3937.0 for survey ft)", Default = 1.0)]
     public double Scale { get; set; }
 
-    [Option('e',"error", Required = false, HelpText = "Base error for root node", Default = 100.0)]
+    [Option('e',"error", Required = false, HelpText = "Base geometric error for the root node, in the model's coordinate units. When 0 (default) it is derived automatically from the model's bounding box diagonal.", Default = 0.0)]
     public double BaseError { get; set; }
 
     [Option("use-system-temp", Required = false, HelpText = "Uses the system temp folder", Default = false)]

Obj2Tiles/Program.cs

@@ -90,17 +90,47 @@ private static async Task Run(Options opts)
                 Console.WriteLine();
                 Console.WriteLine($" => Tiling stage {(gpsCoords != null ? $"with GPS coords {gpsCoords}" : "")}");
 
-                var baseError = opts.BaseError;
+                // Geometric error must be expressed in the model's own coordinate units because it
+                // drives the screen-space-error refinement of every 3D Tiles renderer. A fixed value
+                // is meaningless for models that are not that size, so when the caller does not force
+                // one (--error 0, the default) derive it from the model's bounding box diagonal.
+                var b = decimateRes.Bounds;
+                var modelDiagonal = Math.Sqrt(b.Width * b.Width + b.Height * b.Height + b.Depth * b.Depth);
+                var baseError = opts.BaseError > 0 ? opts.BaseError : modelDiagonal;
+                if (!(baseError > 0)) baseError = 1.0;
+
+                // Coarsest decimated whole-model mesh, used to give the tileset root renderable content
+                // (an empty root tile leaves the model invisible in renderers that do not descend into
+                // the children of a content-less root). Run it through the split stage with 0 divisions,
+                // which keeps it as a single mesh but compresses its textures, so the bootstrap root tile
+                // stays small instead of embedding the full-resolution source textures.
+                string? rootSourceObj = null;
+                if (decimateRes.DestFiles.Length > 0)
+                {
+                    rootSourceObj = decimateRes.DestFiles[^1];
+                    try
+                    {
+                        var rootTempDir = createTempFolder($"{pipelineId}-obj2tiles-root");
+                        await StagesFacade.Split(rootSourceObj, rootTempDir, 0);
+                        var compressedRoot = Directory.GetFiles(rootTempDir, "*.obj").FirstOrDefault();
+                        if (compressedRoot != null)
+                            rootSourceObj = compressedRoot;
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine($" !> Could not compress root mesh ({ex.Message}); using full-resolution coarsest mesh.");
+                    }
+                }
 
                 Console.WriteLine();
-                Console.WriteLine($" => Tiling stage with baseError {baseError}");
+                Console.WriteLine($" => Tiling stage with baseError {baseError:0.000}");
 
                 sw.Restart();
 
                 if (opts.LocalMode && (opts.Latitude != null || opts.Longitude != null))
                     Console.WriteLine(" !> Warning: --local overrides --lat/--lon. ECEF transform will not be applied.");
 
-                StagesFacade.Tile(destFolderSplit, opts.Output, opts.LODs, opts.BaseError, boundsMapper, gpsCoords, opts.LocalMode, opts.Octree);
+                StagesFacade.Tile(destFolderSplit, opts.Output, opts.LODs, baseError, boundsMapper, gpsCoords, opts.LocalMode, opts.Octree, rootSourceObj);
 
                 Console.WriteLine(" ?> Tiling stage done in {0}", sw.Elapsed);
             }

Obj2Tiles/Stages/TilingStage.cs

@@ -12,13 +12,36 @@ namespace Obj2Tiles.Stages;
 public static partial class StagesFacade
 {
     public static void Tile(string sourcePath, string destPath, int lods, double baseError, Dictionary<string, Box3>[] boundsMapper,
-        GpsCoords? coords = null, bool localMode = false, bool isOctree = false)
+        GpsCoords? coords = null, bool localMode = false, bool isOctree = false, string? rootSourceObj = null)
     {
 
         Console.WriteLine(" ?> Working on objs conversion");
 
         ConvertAllB3dm(sourcePath, destPath, lods);
 
+        // Give the tileset root renderable content. The root tile spans the whole model but, in an
+        // octree/multi-tile layout, its geometry lives only in the child tiles, leaving the root
+        // empty (content: null). An empty root is legal per the 3D Tiles spec, but several renderers
+        // (e.g. giro3d's 3d-tiles-renderer, which hardcodes LOAD_ROOT_SIBLINGS) will not descend into
+        // the children of a content-less root, so the whole model never appears. Converting the
+        // coarsest decimated whole-model mesh into "root.b3dm" gives the root a lightweight, complete
+        // representation that is then refined (REPLACE) by the finer child tiles.
+        string? rootContentUri = null;
+        if (rootSourceObj != null && File.Exists(rootSourceObj))
+        {
+            try
+            {
+                var rootB3dm = Path.Combine(destPath, "root.b3dm");
+                Utils.ConvertB3dm(rootSourceObj, rootB3dm);
+                rootContentUri = "root.b3dm";
+                Console.WriteLine($" ?> Generated root content from '{Path.GetFileName(rootSourceObj)}'");
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($" !> Could not generate root content ({ex.Message}); the root tile will be empty.");
+            }
+        }
+
         Console.WriteLine(" -> Generating tileset.json");
 
         double[] rootTransform;
@@ -52,8 +75,11 @@ public static void Tile(string sourcePath, string destPath, int lods, double bas
             Root = new TileElement
             {
                 GeometricError = baseError,
-                Refine = "ADD",
+                // REPLACE (not ADD): the root's coarse whole-model content is superseded by the finer
+                // child tiles as they load, so the two never render on top of each other.
+                Refine = "REPLACE",
                 Transform = rootTransform,
+                Content = rootContentUri != null ? new Content { Uri = rootContentUri } : null,
             }
         };