Rmarkdown: cross-reference image included with markdown syntax

Question

I would like to cross-reference an image which I include with the markdown ![caption with spaces](path/to/image.png) syntax.

I would like to be able to cross-reference this image as \@ref(fig:caption-with-spaces).

I am using bookdown::pdf_document2.

Is this possible?

Answer 1

R Markdown adds a figure ID when generating figures via R, but not for pure Markdown images. In this case, you can add an ID yourself:

![Caption with spaces](path/to/pictures.png){#fig:caption-with-spaces}

The id can be chosen freely, but should start with fig:.

---

If you'd like a keep everything in pure Markdown, but don't want to add identifiers manually, you can use a pandoc Lua filter:

local stringify = (require 'pandoc.utils').stringify
function Image (img)
  if img.identifier == '' then
    img.identifier = 'fig:' .. stringify(img.caption):gsub('%s', '-'):lower()
    return img
  end
end

Use by adding a pandoc_args parameter to your output settings:

output:
  bookdown::pdf_document2:
    pandoc_args: ['--lua-filter', 'auto-image-ids.lua']