ScaleBar on subcoordinate_y is overflowing subcoordinate range

[droumis]

ALL software version info

Software Version Info

Python              :  3.11.10 | packaged by conda-forge | (main, Sep 30 2024, 17:58:42) [Clang 17.0.6 ]
Operating system    :  macOS-13.5.2-arm64-arm-64bit
Panel comms         :  default

holoviews           :  1.20.0b0

bokeh               :  3.6.0
colorcet            :  3.1.0
cudf                :  -
cupy                :  -
dask                :  2024.9.1
dask-expr           :  1.1.15
datashader          :  0.16.3
geoviews            :  -
hvplot              :  0.11.0
ibis-framework      :  -
IPython             :  8.28.0
ipywidgets-bokeh    :  -
jupyter-bokeh       :  -
jupyterlab          :  4.2.5
matplotlib          :  3.9.2
networkx            :  -
notebook            :  6.5.7
numba               :  0.60.0
numpy               :  1.26.4
pandas              :  2.2.3
panel               :  1.5.2
param               :  2.1.1
pillow              :  10.4.0
plotly              :  -
pyarrow             :  17.0.0
pyviz-comms         :  3.0.3
scikit-image        :  -
scipy               :  1.14.1
spatialpandas       :  -
streamz             :  -
tsdownsample        :  0.1.3
xarray              :  2024.9.0

Description of expected behavior and the observed behavior

ScaleBar on subcoordinate_y is overflowing subcoordinate range. The bar length should be limited by the extent of the subcoordinate range.

Complete, minimal, self-contained example code that reproduces the issue

import holoviews as hv
import numpy as np
hv.extension("bokeh")

common_opts = dict(subcoordinate_y=True, scalebar_unit=('cm', 'm'), color='lightgrey')

curves = []
for i in range(10):
    curves.append(hv.Curve(np.random.rand(1000), label=f'c{i}').opts(**common_opts, scalebar=True if i == 5 else False))

curves = hv.Overlay(curves).opts(show_legend=False)

pn.panel(curves.opts(width=800, height=600)).servable()

Stack traceback and/or browser JavaScript console output

Screenshots or screencasts of the bug in action

• [ ] I may be interested in making a pull request to address this

[hoxbro]

This is because of the default options. Try updating to these:

scalebar_opts = {"bar_length": 0.8, "bar_length_units": "data", "length_sizing": "exact"}
common_opts = dict(subcoordinate_y=True, scalebar_unit=("cm", "m"), color="lightgrey", scalebar_opts=scalebar_opts)

[droumis]

I would not have guessed that "bar_length_units" = "data" would be needed to make the bar_length apply to the subcoordinate axis. Even in the bokeh docs: "data" - the length is provided in data space units" does not seem to align with the effect it's having here. I think this should be made to be the default for subcoordinate_y=True so that we don't make users remember this.

[hoxbro]

Agree. I also had it before your suggestions in the original PR.

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