ThinkGeo Raster Sampling Logic & Behavior Matrix¶

Last Updated: February 13, 2026

Core Vision: In ThinkGeo v15.0, we have completely overhauled our raster sampling strategy. By transitioning from a legacy "one-size-fits-all" high-quality interpolation to a modern context-aware, content-adaptive model, we ensure pixel-exact fidelity for thematic data and razor-sharp clarity for digital maps, while maintaining the smooth, high-performance rendering expected for traditional imagery.

1. v14 Preset Behaviors (v14.4.4 Detailed Behaviors)¶

In v14.4.4, raster sampling follows the "Path-First" principle:

Implementation of SKFilterQuality.High¶

In v14's Skia engine, SKFilterQuality.High was an adaptive resampling suite:

1. Upscaling: Uses Bicubic interpolation (Mitchell-Netravali filter).
2. Downsampling: Uses automatic multi-level sampling optimization. The engine dynamically decides whether to enable Mipmap filtering to suppress aliasing.
3. Hardcoded Path: v14 hardcoded this level in DrawImageWithOptimization, covering almost all map-related rendering.

Which scenarios use the "Optimized Drawing Path"? This path forces SKFilterQuality.High: * All TileOverlay base maps: OSM, Google Maps, WMS, WMTS, etc. * All Geographic Layers: RasterLayer, FeatureLayer symbols, etc. * Most UI/Adornment Elements: Compass, Scale bar, Logo, and Icons.

Which scenarios use the "Normal Drawing Path"? Mainly triggered in auxiliary scenarios that bypass the Resize optimization path: * Color Transformations: Images processed via ColorMatrix, HeatStyle, or dynamic colorization. * Direct Bitmap Tools: Utility methods like SKBitmapHelper that render directly to pixels without Canvas optimization.

Note (Independent Path): Printing & Exporting (PrinterGeoCanvas) uses a separate GDI+ path and is unaffected by Skia logic.

2. v15 Preset Matrix (v15+ Architecture)¶

Technical Note: v15.0 migrates to SKSamplingOptions, manually decomposing v14's old "auto-switching" behavior into explicit Mitchell (Upscale) and Linear+Mipmap (Downscale) algorithms.

3. Sampling Decision Matrices¶

3.1 Standard Behavior (v14 / v15-Standard)¶

3.2 Dynamic Mode Content Types¶

Content Type (RasterContentType)	Visual Example (100x100)	Description & Examples	Optimization Goal
Thematic Map (Categorical)		Discrete data. E.g., Land-use, administrative zones, weather warn areas.	Force Nearest: Prevents color bleeding and intermediate colors.
Digital Map (Cartographic)		Vector-style tiles. E.g., OSM tiles, Street maps with labels/lines.	Buffer Nearest: Eliminates filter blur near 1:1 scale for sharp labels.
Imagery (Aerial/Satellite)		Photographic imagery. E.g., Satellite photos, drone captures.	Lock Smoothing: Eliminates pixel shimmering during zoom-out.
Continuous Data (Continuous)		Gradient data. E.g., DEM hillshades, heatmaps.	Lock Smoothing: Maintains fluid transitions.

3.3 Dynamic Mode Decision Matrix¶

(Bold indicates a Content-Specific Override):

Decision Logic Key: 1. 1:1 Divergence: At absolute 1:1, Digital and Thematic maps prioritize "Physical Sharpness" (Nearest), while Imagery follows the Mitchell path. 2. Buffer Zones: Cartographic tiles use a 5% tolerance band around 1:1 to prevent floating-point jitters from causing label blur. 3. Fallback: Imagery / Continuous / Unspecified types follow the 1.0 threshold split (Mitchell if >= 1.0, Linear+Mipmap if < 1.0).

4. Rendering Evolution: Intelligent Inference & Overrides¶

4.1 v14 Limitations¶

• Color Bleeding: Forced interpolation created "fake" colors at categorical boundaries.
• Micro-Scaling Blur: Rounding errors (e.g., 0.999x) triggered filters, making labels fuzzy.
• Tile Seams: Edge anti-aliasing caused faint seams in solid-color maps.

4.2 v15 Dynamic Advantages¶

• Fidelity: Categorical maps stay pixel-exact at all scales.
• Sharpness/No-Seams: Cartographic maps remain razor-sharp and seam-free within the 1:1 buffer.

4.3 Modern Decision Model: Heuristics & Properties¶

v15 utilizes a two-tier decision system to balance automation and control:

1. Class-Level Heuristics (Internal Logic):

   • FeatureLayer: Scans styles. If HeatStyle is present, it uses Continuous; otherwise, it defaults to Cartographic.
   • Internet Layers (Google/Bing/Cloud): Automatically toggles between Imagery and Cartographic based on the map type (e.g., Satellite vs. Street).
   • Protocol Layers (WMS/WMTS/ArcGIS): Defaults to Cartographic to protect the clarity of pre-rendered labels and lines.

2. Instance-Level Overrides (User Overrides):

   • Users can inject custom logic via the RasterContentTypeProvider .NET property without subclassing:

     layer.RasterContentTypeProvider = l => RasterContentType.Imagery;