Add precision argument with default value

[Robinlovelace]

As stated by @mvl22 here cyipt/actdev#10 5 decimal places ~1m accuracy which is probably enough for many purposes assuming 1 km starting size (1/1000 accuracy).

Could be a new arg in the new Params struct, concept I've just discovered!

[Robinlovelace]

Looking at this with reference to the cheatsheet here: https://floating-point-gui.de/languages/rust/

[Robinlovelace]

More useful: https://docs.rs/libmath/0.1.4/math/round/fn.half_up.html

[Robinlovelace]

OK maybe not, only has 4 stars on GitHub: https://github.com/0x022b/libmath-rs Any advice @dabreegster ? I'm still looking and learning.

[Robinlovelace]

Latest thinking: fmt lines only works for printing. Planning to try this approach: https://stackoverflow.com/questions/63214346/how-to-truncate-f64-to-2-decimal-places

[dabreegster]

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=608a9849b07c0916a651d18b7e1a744c
Indeed, the problem is that all of the geo types implement std::fmt::Display, and they don't do any rounding.

The stackoverflow approach is good. I would advise creating a new utility method fn round(poly: &mut Polygon<f64>, precision: usize) and call this at the very end of clockboard. Don't sprinkle the rounding logic everywhere in the code; just post-process the final result. https://docs.rs/geo/0.17.1/geo/struct.Polygon.html#method.exterior_mut should help mutate a Polygon.

[Robinlovelace]

fn round(poly: &mut Polygon, precision: usize)

Sounds like a good idea. Do I need another for loop to iterate over every element? So far I have this but cargo run tells me that this is not good:

fn round(poly: &mut Polygon<f64>, precision: usize) {
    poly.exterior_mut(f64::trunc(before  * 100.0) / 100.0;)
}

[dabreegster]

https://docs.rs/geo/0.17.1/geo/struct.Polygon.html#method.exterior_mut
exterior_mut takes a closure as an argument; that's like a little function without a name. https://doc.rust-lang.org/rust-by-example/fn/closures.html talks about how to use them.

In this case, the closure is given a mutable LineString. If you click through the docs to https://docs.rs/geo/0.17.1/geo/struct.LineString.html, you can see how to work on it. You could figure out how to iterate over its points mutably and then do the truncate.

... But actually as I look at the docs, I spotted https://docs.rs/geo/0.17.1/geo/algorithm/map_coords/trait.MapCoordsInplace.html. This is implemented for Polygon, so all you have to do is follow that example and do the truncate.

[Robinlovelace]

... But actually as I look at the docs, I spotted https://docs.rs/geo/0.17.1/geo/algorithm/map_coords/trait.MapCoordsInplace.html. This is implemented for Polygon, so all you have to do is follow that example and do the truncate.

Awesome, guessed there would be a more direct way. Will give it a spin!

[Robinlovelace]

OK follow-up question, I now have this which seems to be working:

fn round(poly: &mut Polygon<f64>, precision: usize) {
    poly.map_coords_inplace(|&(x, y)| (x + 1000., y * 2.))    
}

pub fn clockboard(
    centerpoint: Point<f64>,
    params: Params,
    boundary: Option<Polygon<f64>>,
) -> Vec<Polygon<f64>> {
    let mut polygons = Vec::new();
    let circle = makecircle(centerpoint, params.distances[0], params.num_vertices); 
    polygons.push(circle);
    polygons
}

How do apply to round function to polygon option? Like this in the penultimate line would seem reasonable to me:

    polygons.round(precision)

But that fails with

cargo run
   Compiling zonebuilder v0.1.0 (/home/robin/github-orgs/zonebuilders/zonebuilder-rust)
error[E0425]: cannot find value `precision` in this scope
  --> src/lib.rs:37:20
   |
37 |     polygons.round(precision)
   |                    ^^^^^^^^^ not found in this scope

[dabreegster]

The error says precision isn't defined. Search through the code for it -- it's right, where's that come from? Remember it's inside params.

Your next issue is that you can't do polygons.round. polygons is a Vec<Polygon<f64>>. If https://doc.rust-lang.org/std/vec/struct.Vec.html doesn't say there's a round method, it's not going to work. The round method you've defined operates on a single Polygon<f64>. So, you need to iterate through the list of polygons and apply the function to each one. See if any of the methods in https://doc.rust-lang.org/std/vec/struct.Vec.html look appropriate

[Robinlovelace]

Think this is good to go. Please review/merge Dustin when you get a chance. Many thanks!

[Robinlovelace]

Closed in #16