Math-Mode – Remove Additional Space Around \underbrace

Question

How do I remove the additional space that is added when using \underbrace{...}, to get the same width in both lines:

\documentclass{scrreprt}

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{amsmath}

\usepackage{beramono}

\begin{document}

\texttt{https://example.org/foo/id/123456789/bar/baz}

$
\underbrace{\texttt{https://example.org/foo}}_{\text{Base-URL}}%
\texttt{/id/}%
\underbrace{\texttt{123456789\vphantom{g}}}_{\text{Foo-ID}}%
\texttt{/}%
\underbrace{\texttt{bar/baz\vphantom{g}}}_{\text{Function}}
$
\end{document}

---

Edit:

Using the approach of Werners answer, I defined a command, because I need this special underbrace without spacing a several times:

...
\newcommand{\underbracewithoutspace}[2]{\mathrlap{\underbrace{\phantom{#1\strut}}_{#2}}#1}

$
\underbracewithoutspace{\texttt{https://example.org/foo}}{\text{Base-URL}}%
\texttt{/id/}%
\underbracewithoutspace{\texttt{123456789}}{\text{Foo-ID}}%
\texttt{/}%
\underbracewithoutspace{\texttt{bar/baz}}{\text{Function}}
$

Answer 1

I would use a combination of \mathrlap and \phantom to get the positioning just right. For \mathrlap you would need the mathtools package. Instead of using \vphantom{g} to get the vertical alignment correct with the other components of your URL, I used \strut, although this may be just a difference in preference.

\documentclass{scrreprt}

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath,mathtools}
\usepackage{beramono}
\begin{document}

\texttt{https://example.org/foo/id/123456789/bar/baz}

$
\mathrlap{\underbrace{\phantom{\texttt{https://example.org/foo\strut}}}_{\text{Base-URL}}}\texttt{https://example.org/foo}%
\texttt{/id/}%
\mathrlap{\underbrace{\phantom{\texttt{123456789\strut}}}_{\text{Foo-ID}}}\texttt{123456789}%
\texttt{/}%
\mathrlap{\underbrace{\phantom{\texttt{bar/baz\strut}}}_{\text{Function}}}\texttt{bar/baz}%
$
\end{document}​

This works fine from a visual/typesetting perspective, but the embedded URL is not properly expanded since it is broken into pieces (for spacing purposes). If you want to maintain a clickable link (using the url package, for example), you would have to do a little more leg work. Here's one approach:

...
\usepackage{amsmath,mathtools,url}
\newcommand{\ubspace}[2]{% Correct \underbrace spacing
  \makebox[\widthof{\texttt{#1\strut}}][c]{\ensuremath{\underbrace{\phantom{\texttt{#1}\strut}}_{\text{#2}}}}
}
...

\begin{document}

\texttt{https://example.org/foo/id/123456789/bar/baz}

$
\mathrlap{%
  \ubspace{https://example.org/foo}{Base-URL}%
  \text{\hphantom{\texttt{/id/}}}%
  \ubspace{123456789}{Foo-ID}%
  \text{\hphantom{\texttt{/}}}%
  \ubspace{bar/baz}{Function}}%
\text{\url{https://example.org/foo/id/123456789/bar/baz}}% Correct clickable URL
$
...