calib-targets-core 0.11.0

Core types and utilities for calibration target detection
Documentation 
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//! Geometry-only smoothness helpers for square labelled grids.

use crate::Coord;
use nalgebra::{Point2, RealField};
use std::collections::HashMap;

fn lit<F: RealField + Copy>(val: f64) -> F {
    F::from_subset(&val)
}

/// Predict a square-grid corner position from complete cardinal neighbor
/// pairs.
///
/// Uses midpoint averaging:
/// horizontal `0.5 * (P(u-1,v) + P(u+1,v))` and vertical
/// `0.5 * (P(u,v-1) + P(u,v+1))`. Returns `None` when neither pair is
/// present.
pub fn square_predict_grid_position<F: RealField + Copy>(
    grid: &HashMap<Coord, Point2<F>>,
    idx: Coord,
) -> Option<Point2<F>> {
    let half: F = lit(0.5);
    let mut pred_sum = Point2::new(F::zero(), F::zero());
    let mut pred_count = 0u32;

    let left = Coord::new(idx.u - 1, idx.v);
    let right = Coord::new(idx.u + 1, idx.v);
    if let (Some(pl), Some(pr)) = (grid.get(&left), grid.get(&right)) {
        let mid = Point2::new(half * (pl.x + pr.x), half * (pl.y + pr.y));
        pred_sum.x += mid.x;
        pred_sum.y += mid.y;
        pred_count += 1;
    }

    let up = Coord::new(idx.u, idx.v - 1);
    let down = Coord::new(idx.u, idx.v + 1);
    if let (Some(pu), Some(pd)) = (grid.get(&up), grid.get(&down)) {
        let mid = Point2::new(half * (pu.x + pd.x), half * (pu.y + pd.y));
        pred_sum.x += mid.x;
        pred_sum.y += mid.y;
        pred_count += 1;
    }

    if pred_count == 0 {
        return None;
    }

    let n: F = lit(pred_count as f64);
    Some(Point2::new(pred_sum.x / n, pred_sum.y / n))
}

#[cfg(test)]
mod tests {
    use super::*;

    fn make_grid(rows: i32, cols: i32, spacing: f32) -> HashMap<Coord, Point2<f32>> {
        let mut map = HashMap::new();
        for v in 0..rows {
            for u in 0..cols {
                map.insert(
                    Coord::new(u, v),
                    Point2::new(u as f32 * spacing, v as f32 * spacing),
                );
            }
        }
        map
    }

    #[test]
    fn predicts_from_horizontal_and_vertical_midpoints() {
        let grid = make_grid(3, 3, 60.0);
        let pred = square_predict_grid_position(&grid, Coord::new(1, 1)).unwrap();
        assert!((pred.x - 60.0).abs() < 1e-6);
        assert!((pred.y - 60.0).abs() < 1e-6);
    }

    #[test]
    fn predicts_from_one_available_pair() {
        let mut grid = HashMap::new();
        grid.insert(Coord::new(0, 1), Point2::new(0.0, 60.0));
        grid.insert(Coord::new(2, 1), Point2::new(120.0, 60.0));
        let pred = square_predict_grid_position(&grid, Coord::new(1, 1)).unwrap();
        assert_eq!(pred, Point2::new(60.0, 60.0));
    }

    #[test]
    fn isolated_points_are_skipped() {
        let mut grid = HashMap::new();
        grid.insert(Coord::new(0, 0), Point2::new(0.0, 0.0));
        grid.insert(Coord::new(5, 5), Point2::new(300.0, 300.0));
        assert!(square_predict_grid_position(&grid, Coord::new(0, 0)).is_none());
    }
}