Documentation or example on adding custom MarkerType on Scatter model

[ccbeloy]

Hi, I’m trying to do a scatter plot that requires using geological standard wells symbols. Attached below.

Can someone guide me to the documentation or example on how to create custom marker type please?

Thanks.

[Bryan]

There is no built-in mechanism for defining custom marker shapes. If the markers are available as raster images that your users can expect to be able to access via a network URL, then you can use image_url to “scatter” small images:

image_url — Bokeh 3.1.1 Documentation

Otherwise, in order to truly create a custom marker you would need to create a custom extension which would require you to supply a JavaScript implementation that does the drawing operations you want, on the HTML canvas:

Custom extensions — Bokeh 3.1.1 Documentation

Note that custom extension are an advanced and still somewhat experimental feature—user extensions may require updating between Bokeh releases.

[ccbeloy]

Is there a way to integrate the image_url into the scatter plot marker option?

Sample code:

markers = hv.dim(“plot_symbol”).categorize({8:‘cross’, 14:‘asterisk’, 2:‘square_cross’, 1:‘circle_cross’, 7:‘square_dot’, 13:‘star’, 12:‘square_x’}, default=‘plus’)

dataplot.opts(hv.opts.Points(tools=[‘hover’], alpha=0.1, hover_alpha=0.2, size=10, show_legend = True, marker=markers, color=‘white’))

[Bryan]

@ccbeloy I can only advise about Bokeh code. Holoviews is a separate project maintained by a different team of people. Questions about HV should be directed at the HoloViz Discourse:

https://discourse.holoviz.org

[ccbeloy]

I posted the same question to Holoviz channel. For the Custom Extension option, do you we a rough guidance on how to properly extend Scattter markers to add custom markers please?

Thanks.

[Bryan]

I am afraid a custom marker is going to be a non-trivial extension. Besides the general documentation and examples I linked above, I can point you at the relevant implementations that are built-in:

The Marker glyph class is defined here:

bokeh/bokehjs/src/lib/models/glyphs/marker.ts at branch-3.3 · bokeh/bokeh · GitHub

It uses the individual drawing operations defined in this separate module:

bokeh/bokehjs/src/lib/models/glyphs/defs.ts at branch-3.3 · bokeh/bokeh · GitHub

to actually do the work of drawing on the canvas.

You’d want to subclass Marker in both Python and JavaScript, and provide your own definition of the JavaScript Marker._render method that does the drawing you want on the canvas.