Installing Gazebo11 side by side with new Gazebo Tutorial (#438)

* Installing Gazebo11 side by side with new Gazebo Tutorial
---------

Signed-off-by: Jose Luis Rivero <jrivero@osrfoundation.org>
Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com>

garden/install_ubuntu.md

@@ -4,7 +4,10 @@ Garden binaries are provided for Ubuntu Focal and Jammy. The
 Garden binaries are hosted in the packages.osrfoundation.org repository.
 To install all of them, the metapackage `gz-garden` can be installed.
 
-**WARNING:** `gz-garden` cannot be installed alongside gazebo-classic (eg. `gazebo11`) since both use the `gz` command line tool. Trying to install `gz-garden` on a system that already has gazebo-classic installed from binaries will cause gazebo-classic and its dependencies to be uninstalled. Currently, the workarounds for this are to install from source or to use Docker [`gazebo-classic`](https://hub.docker.com/_/gazebo) so they are not installed side-by-side on the same system.
+**WARNING:** for gazebo-classic (eg. `gazebo11`) users: `gz-garden` cannot be
+installed alongside with `gazebo11` by default. To facilitate the migration
+this can be done using the instruction detailed in
+[Installing Gazebo11 side by side with new Gazebo](/docs/all/install_gz11_side_by_side).
 
 First install some necessary tools:
 

harmonic/install_ubuntu.md

@@ -1,10 +1,13 @@
 # Binary Installation on Ubuntu
 
-Harmonic binaries are provided for Ubuntu Jammy (22.04) and Ubuntu 24.04 (when it's released). The
+Harmonic binaries are provided for Ubuntu Jammy (22.04) and Ubuntu Noble (24.04). The
 Harmonic binaries are hosted in the packages.osrfoundation.org repository.
 To install all of them, the metapackage `gz-harmonic` can be installed.
 
-**WARNING:** `gz-harmonic` cannot be installed alongside gazebo-classic (eg. `gazebo11`) since both use the `gz` command line tool. Trying to install `gz-harmonic` on a system that already has gazebo-classic installed from binaries will cause gazebo-classic and its dependencies to be uninstalled. Currently, the workarounds for this are to install from source or to use Docker [`gazebo-classic`](https://hub.docker.com/_/gazebo) so they are not installed side-by-side on the same system.
+*WARNING:** for gazebo-classic (eg. `gazebo11`) users: `gz-harmonic` cannot be
+installed alongside with `gazebo11` by default. To facilitate the migration
+this can be done using the instruction detailed in
+[Installing Gazebo11 side by side with new Gazebo](/docs/all/install_gz11_side_by_side).
 
 First install some necessary tools:
 

install_gz11_side_by_side.md

@@ -0,0 +1,71 @@
+# Installing Gazebo11 side by side with new Gazebo
+
+## Supported Gazebo versions and Ubuntu platforms for this tutorial
+
+This tutorial affects the Gazebo Classic users on Ubuntu `Jammy` (latest
+Ubuntu release were Gazebo Classic packages supported by the Gazebo team)
+that plan on migrating code to new Gazebo `Fortress`, `Garden` or `Harmonic.`
+
+There is no guarantee that the Gazebo Classic version detailed in this document
+will be updated in any case. Please consider the migration to the new Gazebo
+as the recommended alternative.
+
+## General context and migrations to new Gazebo
+
+New versions of Gazebo can not be installed together with Gazebo Classic 
+(aka `gazebo11`) since both use the `gz` command line tool. Trying to 
+install `gz-garden` or `gz-harmonic` from `packages.osrfoundation.org` 
+on a system that already has gazebo-classic installed from binaries 
+will cause gazebo-classic and its dependencies to be uninstalled.
+
+Having a side by side installation of both can make easier the recommended
+migration to newer versions of Gazebo.
+
+## Alternative approach for Gazebo Classic without the gz tool
+
+A possible workaround could be to use Gazebo Classic without the `gz`
+command or with a renamed `gz` command. This can be particularly
+interesting since the ROS (Robot Operative System) wrapper known as
+`gazebo_ros_pkgs` do not use the `gz` command but the `gzserver` and
+`gzclient` commands.
+
+Not shipping the `gz` command by default in a Gazebo Classic installation
+would be a disruptive change for existing users so it should not be hosted in
+`packages.osrfoundation.org`.
+
+## Gazebo11 with a separate gz tool package
+
+This alterntive approach has been implemented and packages for `jammy` are
+hosted in the Open Robotics `gazebo11-gz-cli` PPA:
+https://launchpad.net/~openrobotics/+archive/ubuntu/gazebo11-gz-cli
+
+The PPA contains a `gazebo11` version that ships the `gz` executable in
+an independent packages called `gazebo11-gz-cli` while the main `gazebo11`
+package has a `gz11` command. Both are really symlinks to `gz-11.x.y`.
+
+### How the packaging works for the gz command
+
+The `gazebo11-gz-cli` is a soft dependency on `gazebo11`. It is installed
+by default but it will be uninstalled when installing the new Gazebo 
+packages and the effect is that the `gz` command for Gazebo Classic replaced 
+by the `gz` tool from new Gazebo. The `gz11` command can be used instead of
+the `gz` command to access to the same functionality.
+
+## Installing the new packaging from the PPA
+
+From an existing `gazebo11` installation (on `jammy` the Ubuntu official
+repositories will install `11.10.2+dfsg-1` version) or a non existing
+`gazebo11` installation the steps are the following:
+
+```bash
+sudo add-apt-repository ppa:openrobotics/gazebo11-gz-cli
+sudo apt update
+sudo apt-get install gazebo11
+```
+
+If `gazebo11` was installed before, it will be upgraded to the version in the
+PPA. From this point, a new Gazebo installation for `fortress`, `garden` or
+`harmonic` can be executed.
+
+If a new Gazebo installation was installed before, the `gazebo11-gz-cli` package
+won't be installed.