Externalize figures in custom folder (with relative path)

[michaelweinold]

Not a duplicate of #278 and #298.

The prefixoption of the tikzexternalizecommand only works for putting externalized figure in subfolders of the current folder:

\usetikzlibrary{external}
\tikzexternalize[prefix=./externalized/]

Any use of a relative or absolute path pointing to a higher level folder

\usetikzlibrary{external}
\tikzexternalize[prefix=../aux/externalized/]

fails.

project
├───main
│   ├───main.tex
|   └───externalized
└aux
  └externalized