Document Gazebo Camera Integration

[hamishwillee]

Some docs here: PX4/PX4-Autopilot#7625

From @LorenzMeier on slack:

1. Install gstreamer to your system (homebrew is broken, better by hand)
2. In Tools/sitl_gazebo:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a590fef..dc19cee 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,7 +20,7 @@ include(GNUInstallDirs)
 list(APPEND CMAKE_MODULE_PATH /usr/local/share/cmake/Modules)
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
 
-option(BUILD_GSTREAMER_PLUGIN "enable gstreamer plugin" "OFF")
+option(BUILD_GSTREAMER_PLUGIN "enable gstreamer plugin" "ON")
 
 ## System dependencies are found with CMake's conventions
 find_package(PkgConfig REQUIRED)

3. Make a clean build
4. Do

make posix gazebo_typhoon_h480

Should give you a video stream and geo-tagged images

• Camera: https://github.com/PX4/sitl_gazebo/blob/master/src/gazebo_gst_camera_plugin.cpp
• Geotagging: https://github.com/PX4/sitl_gazebo/blob/master/src/gazebo_geotagged_images_plugin.cpp