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Are there any viewers for ImageMarker?

asked 2011-11-17 11:17:09 -0500

I've noticed an ImageMarker message type in visualization_msgs. However in searching for ImageMarker in all my installed stacks and via google, I've found no reference to any package using it anywhere.

Is there some viewer that uses this? Has it been superseded by something else?

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answered 2011-11-17 12:13:49 -0500

Patrick Mihelich gravatar image

There aren't. In fact, rosmsg users visualization_msgs/ImageMarker comes up completely dry.

The problem with ImageMarker is that there's a very simple alternative: just draw your markers/annotations on the input image, publish that as a new topic, and watch in image_view. Why use ImageMarker then?

Pros:

  • Maybe you save bandwidth if you need both the original and marked-up images.

Cons:

  • You get a very limited set of operations.
  • It's cumbersome. If I want to draw circles around a bunch of feature points in an image, it's actually more work to publish a bunch of ImageMarkers than to use cv::circle().
  • Now you have synchronization issues between the marker and image messages.

So, I don't see the use case. You add complexity without gaining a whole lot. Probably ImageMarker was a bad idea from the beginning.

By contrast, visualization_msgs/Marker is useful because it lets you talk to rviz, and because it describes the world. Marker can be understood on its own. rviz integrates data about the world from an arbitrary number of sources, so a Marker topic is just one more channel. Whereas an ImageMarker is useless without the source image, so why separate the two?

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I see utility in much the same way Marker is (if there was a viewer). These plenty of case for being able to turn on and off marker layers IMO. There's a good case for ImageMarker where the original image is processed into several forms (HSV, edge, etc) and especially were by several separate nodes.
Asomerville gravatar imageAsomerville ( 2011-11-18 05:57:28 -0500 )edit
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answered 2019-07-06 13:59:18 -0500

jtbandes gravatar image

We've just released a web-based visualization tool called Webviz that supports ImageMarkers: https://discourse.ros.org/t/webviz-ro...

Because there's no standard "MarkerArray" equivalent for image markers, if you want to publish multiple markers on one topic, you can make your own datatype and add it to this list of imageMarkerArrayDatatypes: https://github.com/cruise-automation/...

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Asked: 2011-11-17 11:17:09 -0500

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Last updated: Jul 06