# Baseline Chart A baseline chart is an area chart split along a horizontal reference level: the portion *above* the baseline is filled with one color (typically green for “good”), the portion *below* with another (typically red for “bad”). Use it when the meaningful question is “are we above or below this number?”, such as performance vs. a benchmark, P&L vs. zero, or latency vs. an SLA. The `base_value` parameter is the y-coordinate of the dividing line. By default it sits at 0, which is the right choice for P&L and other zero-centered quantities; set it explicitly when your baseline is a benchmark return, an SLA, or any non-zero reference. ## What are baseline charts useful for? - **P&L and returns vs. zero**: Above the line is profit; below is loss. The color split makes runs of positive/negative days impossible to miss. - **Performance vs. a benchmark**: Set `base_value` to the benchmark’s return and the chart immediately shows excess/deficit performance. - **SLA / threshold monitoring**: Latency, error rate, or any quantity with a “good vs. bad” threshold reads cleanly as a baseline. - **Index-relative views**: Anything reported as “vs. 100” or “vs. open” benefits from explicit above/below shading. ## Examples ### A basic baseline chart Pass a table with a `timestamp` column and a `value` column. With no `base_value` the chart uses 0 as the baseline. The `tvl.data.values()` series oscillates around 100, so for a meaningful split we set `base_value=100`. ```python order=baseline,data import deephaven.plot.tradingview_lightweight as tvl data = tvl.data.values() baseline = tvl.baseline(data, timestamp="Timestamp", value="Value", base_value=100.0) ``` Sections of the curve above 100 are shaded with the top color; sections below 100 with the bottom color. ### Customize above/below line colors `top_line_color` and `bottom_line_color` set the outline color of the line itself when it’s above/below the baseline. Color kwargs accept a Deephaven theme color (e.g. `"positive"`, `"seafoam-500"`, `"accent-300"`), a hex code (`"#1b5e20"`), a named CSS color (`"darkgreen"`), or an `rgb()`/`rgba()` string for transparency. Theme colors adapt automatically when the user switches themes; hardcoded values do not. ```python order=baseline,data import deephaven.plot.tradingview_lightweight as tvl data = tvl.data.values() baseline = tvl.baseline( data, timestamp="Timestamp", value="Value", base_value=100.0, top_line_color="positive", bottom_line_color="negative", ) ``` The line uses the user’s theme “positive” color above the baseline and “negative” color below. ### Set the baseline at zero for P&L For a P&L series the natural baseline is 0. Gains above, losses below. Build a synthetic P&L by shifting the demo series and set `base_value=0`. ```python order=baseline,pnl import deephaven.plot.tradingview_lightweight as tvl pnl = tvl.data.values().update(["PnL = Value - 100.0"]) baseline = tvl.baseline( pnl, timestamp="Timestamp", value="PnL", base_value=0.0, ) ``` Positive portions of the curve are profit days; negative portions are loss days. ### Line width `line_width` is an integer pixel width from 1 to 4 (the LWC default is 3). Wide lines emphasize the trajectory; thin lines let the colored fill dominate. ```python order=baseline,data import deephaven.plot.tradingview_lightweight as tvl data = tvl.data.values() baseline = tvl.baseline(data, timestamp="Timestamp", value="Value", base_value=100.0, line_width=1) ``` The outline is now one pixel wide. ### Customize the per-half gradient stops Each half of the chart has its own two-stop vertical gradient. Above the baseline, `top_fill_color1` is the stop nearer the line and `top_fill_color2` is the stop nearer the top edge; below the baseline, `bottom_fill_color1` is the stop nearer the line and `bottom_fill_color2` is the stop nearer the bottom edge. Fade either pair toward `"transparent"` to let the chart background show through at the extremes. ```python order=baseline,data import deephaven.plot.tradingview_lightweight as tvl data = tvl.data.values() baseline = tvl.baseline( data, timestamp="Timestamp", value="Value", base_value=100.0, top_fill_color1="positive", top_fill_color2="transparent", bottom_fill_color1="negative", bottom_fill_color2="transparent", ) ``` The above-baseline half fades from a theme “positive” green at the line out to transparent at the top; the below-baseline half fades from a theme “negative” red at the line out to transparent at the bottom. ### Relative gradient and per-point color columns `relative_gradient=True` anchors the two-tone gradient to the series’ value range. Every per-half color can also be driven from a table column: `top_line_color_column` / `bottom_line_color_column` for the line above/below the baseline, and `top_fill_color1_column` / `top_fill_color2_column` / `bottom_fill_color1_column` / `bottom_fill_color2_column` for the gradient stops. ```python order=baseline,data import deephaven.plot.tradingview_lightweight as tvl data = tvl.data.values().update_view( [ "TopLine = `#26a69a`", "TopF1 = `rgba(38,166,154,0.4)`", "TopF2 = `rgba(38,166,154,0.0)`", "BotLine = `#ef5350`", "BotF1 = `rgba(239,83,80,0.4)`", "BotF2 = `rgba(239,83,80,0.0)`", ] ) baseline = tvl.baseline( data, timestamp="Timestamp", value="Value", base_value=100.0, relative_gradient=True, top_line_color_column="TopLine", top_fill_color1_column="TopF1", top_fill_color2_column="TopF2", bottom_line_color_column="BotLine", bottom_fill_color1_column="BotF1", bottom_fill_color2_column="BotF2", ) ``` ## API Reference A baseline series renders an area between the value line and a horizontal "base value", with different gradient fills above (top) and below (bottom) the baseline. Useful for visualizing diff-from-reference quantities (P&L vs 0, return vs index, etc.). **Returns:** `TvlChart` A chart wrapping a single baseline series.