Implement overline in Rust

[dabreegster]

This has a long way to go, but initial results on a large input:

Reading and deserializing cycle_routes_london.geojson
... took 10.795275234s
Running overline on 125317 line-strings
... took 11.485326553s
Aggregating properties on 100230 grouped line-strings
... took 1.990547542s
Writing to output.geojson
... took 877.395391ms

Outstanding tasks:

• [x] Add a CLI
• [ ] Improve performance (parallelize, reconsider the conversion to geo, check parsing and writing)
• [ ] Come up with a simple way of sanely viewing the output to manually validate. geojson.io and similar aren't good for spotting adjacent line-strings; probably make a custom Leaflet style
• [ ] Optionally split when some property (an OSM ID) changes
• [ ] Ignore direction (optionally?)
• [ ] Split line segments when needed
• [ ] Write a bunch of tests
• [ ] Validate to the R implementation's output, and compare performance

[Robinlovelace]

:rocket:

[dabreegster]

What're the ways to aggregate/deal with properties? So far:

enum Aggregation {
    /// Copy the value of this property from any input feature containing it. If the property
    /// differs among the input, it's undefined which value will be used.
    KeepAny,
    /// Sum this property as a floating point.
    SumFloat,
}

Average/mean is also used, right? We could also have something to collect all unique values into an array, if that's ever used

[Robinlovelace]

Sum, mean, first, last. At some point "the value associated with the longest section of linestring that fed into the segment"

[Robinlovelace]

Max, min, and x percentile (e.g. 85% percentile speeds) could be useful one day.

[dabreegster]

What do first and last mean -- min and max of a numeric?

[Robinlovelace]

min and max of numeric, yes. first can just mean the first appearance in the order that the input is read-in so kind of random.

[dabreegster]

Open viewer.html from the latest commit in a browser, load an output geojson file (from the new or old overline implementation, doesn't matter). It uses line thickness to display numeric properties. Think this'll work for manually inspecting test output?

[dabreegster]

Merging now and adding an issue for all the half-done work mentioned earlier