Add distance(nodeset<geopoint> | geoshape | geotrace) function

[lognaturel]

https://opendatakit.github.io/xforms-spec/#fn:distance

getodk/xforms-spec#129

[dcbriccetti]

Just to clarify,

Returns the distance in meters of either a nodeset of geopoints or a single geoshape value or a single geotrace value (not a combination of these) on Earth, in the sequence provided by the points in the parameter. It takes into account the circumference of the Earth around the Equator and does not take altitude into account.

This distance is the sum of the great circle distances (arcs over the Earth’s surface) between each point and the previous, starting with the 2nd point. Yes?

[lognaturel]

Yes, that is how I understand it. Perhaps we should use your wording in the spec, it’s nice and clear.

[dcbriccetti]

I’m coordinating with Martijn on a common implementation and shared tests, and after reading some background from him, think we should leave the area calculation alone, despite its imprecision.

[dcbriccetti]

I’ve discovered that the area calculator web tool used to generate test data for our area calculation doesn’t close the polygon when producing its perimeter. The 2,076 meter value is the sum of the lengths of the four sides between the five points moving anti-clockwise from the top-right point.

So, in our tests using this data, we also won’t close the polygons for perimeter calculations.

[lognaturel]

That sounds right. The calculation should use the points defined by the expression passed in and not add any. In the case of a geoshape argument, the first and last point will be the same.

[dcbriccetti]

Good to know. Thanks!

[dcbriccetti]

Getting close to done here.

[dcbriccetti]

OK, reviewers, at your convenience. 3 PRs. 302–304. I’m thinking 15–25 minutes would be needed. And if you like, I’ll even walk you through it if we can coordinate our schedules.

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[dcbriccetti]

Silly bot. Can’t you read?

[getodk-bot]

Hello @dcbriccetti, you claimed this issue to work on it, but this issue and any referenced pull requests haven't been updated for 7 days. Are you still working on this issue?

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[dcbriccetti]

I need to complete so that it satisfies:

Returns the distance in meters of either a nodeset of geopoints or a single geoshape value or a single geotrace value