RE: MapML encoding of video features

Hi Rob,

> 1. ... It might help others to more easily understand these features if you made a sequence of simple examples, e.g. how to add a marker with a label, how to draw a path, how to draw basic shapes, etc. 

Yes, that would be ideal.  I started writing tutorials with "how to make a map with MapML": and I intend to extend it as time and resources allow.  I was thinking that since vector MapML is more experimental at this point, that after Testbed 14 is done will be a good opportunity to extend the documentation.  I would like to get other contributors involved, and I hope that I can bring the client code base closer to compatibility with the just-released Leaflet 1.3.0, in the further hope that we can find some common opportunities with the Leaflet.js core contributors.

> 3. Is it possible to draw a circle in non-CSS pixel units with MapML? For example, how can I draw a 10-metre radius circle around the Greenwich Observatory at 51.48N, 0.00E?

The intent of MapML vectors is to rely on OGC Simple Features for the geometry model.  As such, I believe (anyone with better knowledge than this please correct me) that a circle is easily represented by a Polygon with the vertexes arranged approximately in a circle. So, in order to enable simple client-side creation of circles as features using WGS84, we would have to either extend the standard or do it imperatively, via a attribute/property/ API method on the <layer> element, or something similar.  Certainly worth discussing!  Maybe you could join the Maps for HTML cg and we can design something through email over there.

> 4. The HTML5 video element already supports metadata tracks, so I propose:
<h1>Search and Rescue Drone flight path 2018-12-22</h1>
<video width="640" height="360">
    <source src="flight-2018-12-22.webm” type=“video/webm”>
    <track src=“flight-2018-12-22.meta” kind=“metadata">
    Your browser does not support HTML5 video.

where the flight-2018-12-22.meta file contains the associated map annotation details, e.g. draw a line using a list of path co-ordinates at given times, in a suitable standard format.

Yes, I think that would be ideal. I see that tracks can contain structured info, including html markup or json objects. (Why not MapML?). The important thing for such tracks would be to relate sequences from the video / audio to locations on a map. The task then is to define a reliable way to do that.  If the video/audio element is (part of) a property of a MapML feature, that is a predefined scope for the relationship, no? That is to say, that a video in an HTML document, despite that it might be have a track that contains coordinates of a path, how(why?) would you create an API to access that info if maps weren't part of HTML?  OTOH, if maps are built-in to HTML, you could associate the video/audio track to maps in different ways, I think.  I think this is fertile ground.

> I’m unclear about the aim of your ‘balloon’ example. Which problem is it trying to address? Firstly, the video-related feature does not link the path co-ordinates to any timing information in the video. I presume that the ‘balloon’ is equivalent to a Leaflet Popup:, i.e. an HTML display container floating over the map and associated with a location marker. 
Yes I used 'balloon' to mean what is described as 'popup' by leaflet.

> Assuming I’ve understood correctly so far, the video and map elements will be competing for the same display space, as a significant part of the map will be obscured by the video near the point of interest, which seems counterproductive.
> Firstly, the video-related feature does not link the path co-ordinates to any timing information in the video.

I guess there are different modes in which to manage the relationship between video and map.  One is as a balloon/popup.  In that case the balloon hides some of the map, yes. But it has the advantage of pointing to a spot.  Maybe the track metadata could guide where it points to as the video/audio plays. Another is like we see in the Leaflet documentation, where a video is treated like an image overlay feature (static).  I don't know if there's any value in georeferenced track info  /metadata in that use case.  What do you think? Finally, maybe you could control the map via its api using track location information as the video/audio plays. I think this is more of a scripting use case, but you could probably figure out how to do it declaratively too.

Interesting discussion!


Peter Rushforth

Technology Advisor
Canada Centre for Mapping and Earth Observation / Earth Sciences Sector
Natural Resources Canada / Government of Canada / Tel: 613-759-7915

Conseiller technique
Centre canadien de cartographie et d’observation de la Terre / Secteur des sciences de la Terre
Ressources naturelles Canada / Gouvernement du Canada / Tél: 613-759-7915

Received on Monday, 15 January 2018 19:52:00 UTC