Compressed Image Display

[mjforan]

Addresses #738

I added RosTopicMultiProperty, which extends RosTopicProperty with a list of message types instead of one single type. This allows the ImageDisplay to show raw and compressed image topics together in its selector list. ImageDisplay was altered to use an image_transport subscriber so it can seamlessly display any installed image type. There is also a handful of frivolous changes to comply with the style linters.

Tested with raw and compressed images. Assuming the other types work as well because the conversion happens in the image_transport library.

Uncertainties:

• RosTopicMultiProperty: Is the name ok? Is there a simpler way to achieve my goal without adding a one-off property?
• plugin_description.xml: I added the other image_transport topic types here so Image Display appears in the "Add/By topic" menu. Adding the display will fail if the associated image_transport plugin is not installed. Should ros-$ROS_DISTRO-image-transport-plugins be added to package.xml?

[mjforan]

Added a property to manually override image transport type. Rviz determines the transport by checking the topic name against image_transport conventions, e.g. camera_name/raw, camera_name/compressed, etc. If this is not the case, the transport must be set manually.
I also fixed the crash caused by adding a topic with an unavailable transport. Instead it will provide an error on the status property saying the transport is not installed.

[ahcorde]

This is wierd

I had a default rviz.config file with an image display and Rviz2 crashes, do you mind to take a look ? we don't want to break user.

[mjforan]

@ahcorde

This is wierd

Sorry about that, I have pushed a fix.

I had a default rviz.config file with an image display and Rviz2 crashes, do you mind to take a look ? we don't want to break user.

Please provide details so I can reproduce your issue.

[mjforan]

I would like to list the available image transports in a status message. However, setStatusStd only seems to work when it is called from subscribe, not onInitialize or updateTopic. Any idea why?

The status message doesn't really matter except the transport->message type map is hard-coded, so we will want a warning if a new transport type is used which does not exist in the map.

[mjforan]

I noticed the Jazzy version of image_transport finally allows passing in custom QoS so I updated the API here to match. This change is not compatible with previous versions of ROS.

[mjforan]

Can ImageDisplay be combined with the parent class ImageTransportDisplay? That would allow CameraDisplay to also show compressed image topics.