project path in Rmd

Dear useRs,

I believe this is R code so appropriate for this list, but let me know
if this relates more to RStudio itself.

I am working on an RStudio project. In that project directory, I have a
folder called 'analysis' and in there a folder called 'scripts'
('~/analysis/scripts').
My data files needed for the scripts are in '~/analysis/raw_data' and
the output should be in '~/analysis/derived_data'.

My scripts are Rmd files, so when I knit them, their working directory
is where they are located, i.e. '~/analysis/scripts'. The problem I
then
have is to specify the path for 'raw_data' and 'derived_data' since
during the rendering I am not relative to the project directory
anymore.
And these folders are not subfolders of the working directory?
'~/analysis/scripts'.
I hope I am clear here...

I would like to avoid absolute paths of course, but I do not know how
to
proceed.
What would be nice is a way to get the project directory in the
scripts,
rather than their working directory.
Does that make sense?

Thank you in advance
Best,
Ivan