Cannot fix aspect ratio and remove padding simultaneously

I am trying to plot an image using the xarray accessor, but can’t seem to be able to specify the aspect ratio and also remove padding simultaneously.

Demonstration:

import xarray as xr
import hvplot.xarray  # noqa

air_ds = xr.tutorial.open_dataset('air_temperature').load()
air2d = air_ds.air.sel(time='2013-06-01 12:00')

default behaviour

air2d.hvplot.image()

air2d.hvplot.image().opts(data_aspect=True)

air2d.hvplot.image(padding=0)

air2d.hvplot.image(padding=0).opts(data_aspect=True)

I would have expected the last figure not to have any padding at the sides.

This shows that I can’t currently choose my axis to have the same aspect ratio as the data, and also remove all padding simultaneously. I don’t know whether this is a bokeh problem or a hvplot problem, but I thought I would raise it here first.

I also tried setting xlim but that did not remove the padding either.

[Hoxbro]

Two things that might work:

1. Run air2d.hvplot.image(data_aspect=True)
2. Manipulate the frame_width / frame_height to match the ratio of data_aspect.

frame_height = 300
data_aspect = 1

ratio = (air2d.lon.max() - air2d.lon.min()).values /  (air2d.lat.max() - air2d.lat.min()).values
frame_width = int(ratio * frame_height / data_aspect)
air2d.hvplot.image().opts(data_aspect=data_aspect, frame_width=frame_width, frame_height=frame_height)

[jbednar]

Oh! I didn’t spot that in your response! Ah, this is an interaction between hvPlot and HoloViews, then. I think hvPlot sets the height and width when it hands things over to HoloViews, and once that’s happened, HoloViews sees data_aspect, height, and width as all having been specified by the user, and thus tries to achieve all three instructions. When data_aspect is given to hvPlot directly, it can take effect before height and width are given values in hvPlot.

So it’s great that there is a reasonable way to achieve the desired behavior, but it’s not at all a good situation, because having data_aspect behave so differently depending on whether it’s passed to hvPlot or HoloViews is very tricky and subtle. I think I’ve noticed similar issues with responsive and sizing_mode, i.e. things where it matters whether a height or width has been set explicitly by the user. Definitely a topic for someone who knows that interface between hvPlot and HoloViews better than I do to address!