Include building metadata in OBJ and COLLADA files

[bcamper]

In addition to the GeoJSON files, let's include building properties in the OBJ and COLLADA files, to simplify usage (no need to request multiple files).

• OBJ: we can use a stringified JSON object in a comment (since there is no standard format support for metadata).
• COLLADA: we can put something in the XML (is there a metadata standard?).

[robhawkes]

As a start, I've implemented the existing method that I used with the original Polygon City – this adds simple comments to the top of the obj file for each of the origin longitude/latitude and the elevation. For the collada files I've added longitude, latitude and elevation properties to the document structure.

For example…

obj:

# Longitude: 14.270778949915217
# Latitude: 48.244130368992465
# Elevation: 266.506

...

collada:

<?xml version="1.0"?>
<collada version="Thu Jan 04 2001 00:00:00 GMT+0000 (GMT)">
    <asset>
        <created>Thu, 11 Feb 2016 13:00:28 GMT</created>
        <modified>Thu, 11 Feb 2016 13:00:28 GMT</modified>
        <unit name="meter" meter="1"/>
        <up_axis>Y_UP</up_axis>
        <longitude>14.270778949915217</longitude>
        <latitude>48.244130368992465</latitude>
        <elevation>266.506</elevation>
    </asset>

...

Happy to change the structure and naming of these as I just went with something simple to start with.

[bcamper]

Sounds good. Maybe we could also include a stringified JSON blob to make it easier to parse all properties out at one time, but could also keep the more human- (and machine-) readable versions you have?

[bcamper]

(I mean for OBJ, COLLADA already supports reasonably structured data)

[robhawkes]

That's a good idea – I've pushed an update that places a JSON string as the first line of an obj, and also includes the same string in a 'metadata' tag in the collada header.

# {"id":"linz-ID_3467","idOriginal":"ID_3467","origin":[14.274986011132702,48.32885736798415],"elevation":307.76}
# Longitude: 14.274986011132702
# Latitude: 48.32885736798415
# Elevation: 307.76

...

[bcamper]

This is a small nitpick but perhaps we could prefix the JSON with something like Properties, e.g.:

# Properties: {"id":"linz-ID_3467", ...

To make it a bit more reliable parsing wise? Basically someone is going to have to look for a regex or make other format expectations to parse these, so the more precise we can be about it the better.

[robhawkes]

It's easy enough to change – the reason it isn't prefixed at the moment is in my head imagined it was easier to know that the first line is always the JSON and to get to it you need to only remove the # comment prefix.

I'll change it for now and we can always change it back if we want.