It is possible to use an online panorama generator to make an horizon file for CdC.

In the form set your coordinates, here an example for Annecy, France.
Be sure to set “Left edge=90”, “Right edge=90”, “Tilt=0”, “Elev. exaggeration=1”.

Show the panorama, use the function in your web browser to save the page in a new directory, be sure the option to save the complete web page is selected.

This result in the following image files in the directory. You can delete the other files.

Assemble this images in GIMP (a bit tedious) or using the simple “montage” command from ImageMagick.

magick montage 20250820* -mode Concatenate  -tile x1 annecy.png

This is the result, you can now follow the instruction to generate an horizon file for CdC using this panorama.
The main operation is to make the sky area transparent.