3D Tilesの出力結果を微調整 (#649)

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### What I did（変更内容）
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introduces. -->
<!-- どのような変更をしますか？ 目的は？ -->

- 出力結果を微調整する

### Notes（連絡事項）
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None / なし

nusamai/src/sink/cesiumtiles/mod.rs

@@ -119,7 +119,7 @@ impl DataSink for CesiumTilesSink {
         let tile_id_conv = TileIdMethod::Hilbert;
 
         // TODO: configurable
-        let min_zoom = 12;
+        let min_zoom = 15;
         let max_zoom = 18;
 
         let limit_texture_resolution = self.limit_texture_resolution;
@@ -409,8 +409,8 @@ fn tile_writing_stage(
             // initialize texture packer
             // To reduce unnecessary draw calls, set the lower limit for max_width and max_height to 4096
             let config = TexturePlacerConfig {
-                width: max_width.max(4096),
-                height: max_height.max(4096),
+                width: max_width.max(2048),
+                height: max_height.max(2048),
                 padding: 0,
             };
 

nusamai/src/sink/cesiumtiles/slice.rs

@@ -138,7 +138,7 @@ pub fn slice_to_tiles<E>(
                                     tiling::scheme::zxy_from_lng_lat(zoom, lng_center, lat_center);
                                 tiling::scheme::geometric_error(zoom, y)
                             };
-                            let threshold = geom_error * 1.5; // TODO: adjustable
+                            let threshold = geom_error * 2.0; // TODO: adjustable
                             if approx_dx < threshold
                                 && approx_dy < threshold
                                 && approx_dh < threshold