Backends

The viz service selects the rendering backend based on mark types and coordinate system.

Backend selection

Backend	When used	Mark types
ECharts	2D / 3D charts, Cartesian / polar / parallel coordinates	Point (2D+3D), Line (2D+3D), Bar, Histogram, Box/Violin, Candle, Parallel, Partition, Sector, Surface, Contour, Flow, VectorField
VTK	3D scientific visualization	Voxel, MeshCell
DeckGL	Geospatial maps, GEO coordinates	Choropleth, Point (with lat/lon)
Graph	Network visualization	Node (with edge data)
HTML	Raw HTML embedding	Text / KPI cards

ECharts Backend

backends/echarts_backend.py

Renders 2D and 3D charts using Apache ECharts (+ echarts-gl for 3D). Supports:

• Scatter, line, bar, histogram, box, candle, parallel, sunburst/treemap
• Polar bar, pie/donut (sector)
• 3D scatter, line, surface, flowGL
• Violin + contour via Apache's echarts-custom-series bundles
• Theme tokens read inline per mark (no post-processor)

VTK Backend

backends/vtk_backend.py

Renders 3D scientific visualizations using VTK. Supports:

• Surface meshes with color mapping
• Contour plots (2D/3D iso-surfaces)
• Volumetric rendering (voxel, uniform grid)
• Unstructured mesh cells
• Cube axes, color bars, camera controls

DeckGL Backend

backends/deckgl_backend.py

Renders geospatial visualizations using Deck.GL. Supports:

• Choropleth maps (GeoJSON polygons)
• Point layers on maps
• Color-coded regions
• Tooltips and hover interactions

Graph Backend

backends/graph_backend.py

Network/graph visualization using force-directed layout.

HTML Backend

backends/html_backend.py

Embeds raw HTML content (e.g., custom widgets, embedded content).