2D contour map from xyz column data

Dear Bokeh Team and users,

Could you someone help us to plot 2D contour map from externally saved .text file ( three column: x-coordinate, y-coordinate and z-intensity) using Bokeh?

x and y are not evenly spaced (irregular) and for each (x,y) point there is intensity as z column.

Thanks in advance!

Jas

Can you define what you mean by “2D contour map”? Do you mean a colormapped image (that implicitly shows iso-levels as a result of the encoding into a discrete set of colors)? Or do you mean a “topographic” map, i.e. a collection of iso-contour lines?

Hi!

Its 1st one: colormapped image with out contour lines.
I have three column data x y z separated by space (please see the attached image).
y column increases in 0.5 steps (15 to 60) while for each y I have x (from -2 to 2) in step 0.02.
z column is the intensity for each (x,y) point.
It can be imagined as a matrix as 2-dimensional (x,y) space where we assign z as intensity on each (x,y).

I would like to plot all the (x,y) points in 2-dimension [x-coordinate, y-coordinate] and we will assign the corresponding z-values (intensity) as color.

I guess it can be done using other software but I like and feel Bokeh has its own fascinating way to plot and use fantastic colors :slight_smile:

Cheers!

The image glyph method is probably the simplest option, it accepts a palette name (or you can pass an explicitly configured ColorMapper instance). You can see an example to emulate here:

https://docs.bokeh.org/en/latest/docs/gallery/image.html

Hi again,
I am very much beginner.
Could you please have a look on the attached figure
You will find the comments I made using #…

Hi @jasman please always prefer to post code as actual formatted text, and not as screenshots Using screenshots means that other people cannot copy and paste parts fo it when they have questions. For instance, I am not sure what you mean when you ask

# how we can assign 'z' column here?

It’s not clear to me what you actually want to happen. If you just want a different name, you can replace the variable name d with z throughout, but I have to suspect you mean something more/different.

Hi,

I have one example done with the help of matplotlib

Lines after 146 (it is a bit hard to see what goes in and the code might contain some errors)

And example of the output

https://arviz-devs.github.io/arviz/examples/bokeh/bokeh_plot_kde_2d.html

I have done this successfully using the matplotlib tricontour function. You can mostly follow https://matplotlib.org/3.1.0/gallery/images_contours_and_fields/tricontour_demo.html , except you’ll need a bit of array/data manipulation to transform the tricontour object into something you can plot in bokeh, i.e. an image or a column datasource containing x/y arrays for multiple patch objects representing each contour).