Add GeoJSON support

[latin-panda]

Useful links

• GeoJSON specs
• ODK Collect specs

Description

The default Geopoint question type was added as part of this work. It must support GeoJSON, too.

Evaluate the codec and see how to fit GeoJSON; maybe external secondary serialization to use the same encoding logic.

[lognaturel]

I believe there's already support for geojson external secondary instances! There are two aspects to that:

• properties are made available like they would be for a CSV attachment or internal choice list
• geometry is made available through a special well-known geometry property

You can validate that the former is working by doing a select_one_from_file on a geojson file like cities.geojson.zip. You should see a list of all options.

For the second, let's say you have that select_one_from_file cities.geojson and the field name is city. You should be able to do something like have a calculate on a geopoint question with calculation instance('cities')/root/item[name = ${city}]/geometry and the geopoint question should show the location of the selected city. It's possible this second part doesn't work yet, I'm not sure.