How to add multiple xmp properties?

[kfarr]

I am trying to add geospatial data to an exported glb file. I was able to follow the example here and export one property. How do I export more than one property? When I try a naive approach of setting more than one packet, only the last packet values are applied to the output GLB. I must be missing something simple?

https://gltf-transform.dev/modules/extensions/classes/KHRXMP

Snippet from my naive approach:

    // Create Packet property.
    let packet = null;
    
    packet = xmpExtension.createPacket()
    .setContext({
        geo: 'https://kieranfarr.com',
    })
    .setProperty('geo:version', '0.1')

    packet = xmpExtension.createPacket()
    .setContext({
        geo: 'https://kieranfarr.com',
    })
    .setProperty('geo:longitude', metadata.longitude ?? 0)
    root.setExtension('KHR_xmp_json_ld', packet);

only longitude shows up, not version

[donmccurdy]

Two things that might be helpful —

(1) The document root can only have one packet, but a packet can have multiple properties. For example:

 packet = xmpExtension.createPacket()
    .setContext({geo: 'https://kieranfarr.com'})
    .setProperty('geo:version', '0.1')
    .setProperty('geo:longitude', metadata.longitude)
    .setProperty('geo:latitude', metadata.latitude);

root.setExtension('KHR_xmp_json_ld', packet);

(2) Additional packets may be added to other objects within the document, such as nodes or scenes. So for example, two nodes could have different lat/lng properties, via two different packets. The root is just one of the possible places to attach a packet.

[kfarr]

You're right! I had tried that earlier but assumed that Babylon Sandbox would enumerate all the values without scrolling down to the bottom. Now I see all the values are in there:

I'm surprised nobody has created a geo metadata schema? Should I throw one together? It's very basic

[donmccurdy]

Huh, not sure why it lists just the first property in the UI!

It's a good question about creating a new schema/namespace, there is exif:GPSLatitude and exif:GPSLongitude but whether the EXIF namespace is appropriate to use in glTF models, I have no idea! Might need to be raised on the glTF spec repo if you want a "blessed" solution, but using a custom namespace and schema is totally fine too, depending on the needs.

[kfarr]

Thanks! This worked, here's the PR that seems to do the job
https://github.com/3DStreet/3dstreet/pull/1069/files#diff-71fe3463c9d08b52ebfdd690d02b81a1c0f75d992f4d68e0827fa6d1c3614acbR74