Small mesh: real data in the Vega/Vega-Lite export

Figure.to_vega()/to_vega_lite() normally embed a pcolormesh as a single rasterized image – a picture of the data, frozen at whatever color scale existed at export time. For a mesh small enough to stay cheap (at most ~2000 cells, a rectilinear grid, a plain linear color norm, and a colormap with a matching named Vega scheme – this one easily qualifies at 10x8 = 80 cells), mesh_data=True embeds the real per-cell values instead, as genuine field/scale-encoded marks: reactive to a downstream color scale change, and queryable by anything reading the spec, not just a picture of the result.

This page’s own Vega/Vega-Lite export links (below the gallery image) show that live: open either one and each mesh cell is a real rect, not a <image> – unlike the large mesh in the plain pcolormesh example, which stays a rasterized image regardless, above the cell limit where a per-cell export would stop being cheap.

Live figure — pick a tool, then zoom, pan, point-pick or annotate. Nothing is active until a tool is selected.

View this figure’s Vega export ↗ — the raw JSON spec, rendered live by a real Vega engine.

View this figure’s Vega-Lite export ↗ — the raw JSON spec(s), rendered live by a real Vega-Lite engine.

import numpy as np
import plotpress

x = np.linspace(0, 10, 11)
y = np.linspace(0, 6, 9)
X, Y = np.meshgrid(x, y)
Z = np.sin(X / 2) * np.cos(Y / 2)

fig, ax = plotpress.subplots()
mesh = ax.pcolormesh(x, y, Z, cmap="viridis")
ax.set_title("small mesh -- 10x8 cells")
fig.colorbar(mesh, ax=ax)