app.py

import numpy as np
import holoviews as hv
import dask.dataframe as dd

from holoviews import opts
from holoviews.operation.datashader import aggregate
import panel as pn
from utils import get_meta_data

pn.extension()

hv.extension('bokeh')

renderer = hv.renderer('bokeh')

opts.defaults(
    opts.Curve(xaxis=None, yaxis=None, show_grid=False, show_frame=False,
               color='orangered', framewise=True, width=100),
    opts.Image(width=800, height=400, shared_axes=False, logz=True, colorbar=True,
               xaxis=None, yaxis=None, axiswise=True, bgcolor='black'),
    opts.HLine(color='white', line_width=1),
    opts.Layout(shared_axes=False),
    opts.VLine(color='white', line_width=1))

pandas_df = pn.cache(get_meta_data)()
df = dd.from_pandas(pandas_df).persist()

points = hv.Points(df, kdims=['centre_easting', 'centre_northing'], vdims=[])

agg = aggregate(points, link_inputs=True, x_sampling=0.0001, y_sampling=0.0001)

agg.opts(cmap="kr_r")

pointerx = hv.streams.PointerX(x=np.mean(points.range('centre_easting')), source=points)
pointery = hv.streams.PointerY(y=np.mean(points.range('centre_northing')), source=points)
box = hv.streams.BoundsXY(source=points, bounds=(0,0,0,0))
vline = hv.DynamicMap(lambda x: hv.VLine(x), streams=[pointerx])
hline = hv.DynamicMap(lambda y: hv.HLine(y), streams=[pointery])

tiles = hv.Tiles('https://tile.openstreetmap.org/{Z}/{X}/{Y}.png', name="OSM").opts(width=600, height=550)
hvobj = tiles * agg * hline * vline

@pn.depends(pointerx.param.x, pointery.param.y)
def table(x,y):
    return f"Easting: {x}, Northing: {y}"

@pn.depends(box.param.bounds)
def bbox(value):
    return str(value)

pn.pane.HoloViews(hvobj).servable()

pn.panel(table).servable()
pn.panel(bbox).servable()