ringgrid 0.5.5

Pure-Rust detector for coded ring calibration targets
Documentation 
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use super::{PixelMapper, RadialTangentialDistortion, UndistortConfig};
use serde::{Deserialize, Serialize};

/// Pinhole camera intrinsics.
#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
pub struct CameraIntrinsics {
    /// Focal length in x (pixels).
    pub fx: f64,
    /// Focal length in y (pixels).
    pub fy: f64,
    /// Principal point x (pixels).
    pub cx: f64,
    /// Principal point y (pixels).
    pub cy: f64,
}

impl CameraIntrinsics {
    /// Returns `true` when focal lengths are finite and non-zero.
    pub fn is_valid(self) -> bool {
        self.fx.is_finite()
            && self.fy.is_finite()
            && self.cx.is_finite()
            && self.cy.is_finite()
            && self.fx.abs() > 1e-12
            && self.fy.abs() > 1e-12
    }

    /// Convert pixel coordinates to normalized pinhole coordinates.
    pub fn pixel_to_normalized(self, pixel_xy: [f64; 2]) -> Option<[f64; 2]> {
        if !self.is_valid() {
            return None;
        }
        let x = (pixel_xy[0] - self.cx) / self.fx;
        let y = (pixel_xy[1] - self.cy) / self.fy;
        if x.is_finite() && y.is_finite() {
            Some([x, y])
        } else {
            None
        }
    }

    /// Convert normalized pinhole coordinates to pixel coordinates.
    pub fn normalized_to_pixel(self, normalized_xy: [f64; 2]) -> [f64; 2] {
        [
            self.fx * normalized_xy[0] + self.cx,
            self.fy * normalized_xy[1] + self.cy,
        ]
    }
}

/// Complete camera model (intrinsics + radial-tangential distortion).
///
/// Implements [`PixelMapper`], making it usable directly with
/// [`Detector::detect_with_mapper`](crate::Detector::detect_with_mapper)
/// for distortion-aware detection.
///
/// # Example
///
/// ```no_run
/// use ringgrid::{BoardLayout, CameraIntrinsics, CameraModel,
///                Detector, RadialTangentialDistortion};
/// use std::path::Path;
///
/// let camera = CameraModel {
///     intrinsics: CameraIntrinsics {
///         fx: 900.0, fy: 900.0, cx: 640.0, cy: 480.0,
///     },
///     distortion: RadialTangentialDistortion {
///         k1: -0.15, k2: 0.05, p1: 0.0, p2: 0.0, k3: 0.0,
///     },
/// };
///
/// let board = BoardLayout::from_json_file(Path::new("target.json")).unwrap();
/// let detector = Detector::new(board);
/// let image = image::open("photo.png").unwrap().to_luma8();
/// let result = detector.detect_with_mapper(&image, &camera);
/// ```
#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
pub struct CameraModel {
    /// Camera intrinsics.
    pub intrinsics: CameraIntrinsics,
    /// Distortion coefficients.
    pub distortion: RadialTangentialDistortion,
}

impl CameraModel {
    /// Distort an undistorted pixel point into image pixel coordinates.
    pub fn distort_pixel(self, undistorted_pixel_xy: [f64; 2]) -> Option<[f64; 2]> {
        let xn = self.intrinsics.pixel_to_normalized(undistorted_pixel_xy)?;
        let xd = self.distortion.distort_normalized(xn);
        let pix = self.intrinsics.normalized_to_pixel(xd);
        if pix[0].is_finite() && pix[1].is_finite() {
            Some(pix)
        } else {
            None
        }
    }

    /// Undistort a pixel point with default iterative settings.
    pub fn undistort_pixel(self, distorted_pixel_xy: [f64; 2]) -> Option<[f64; 2]> {
        self.undistort_pixel_with(distorted_pixel_xy, UndistortConfig::default())
    }

    /// Undistort a pixel point with custom iterative settings.
    pub fn undistort_pixel_with(
        self,
        distorted_pixel_xy: [f64; 2],
        cfg: UndistortConfig,
    ) -> Option<[f64; 2]> {
        let xd = self.intrinsics.pixel_to_normalized(distorted_pixel_xy)?;
        let mut x = xd[0];
        let mut y = xd[1];

        for _ in 0..cfg.max_iters.max(1) {
            let r2 = x * x + y * y;
            let r4 = r2 * r2;
            let r6 = r4 * r2;
            let radial =
                1.0 + self.distortion.k1 * r2 + self.distortion.k2 * r4 + self.distortion.k3 * r6;
            if !radial.is_finite() || radial.abs() < 1e-12 {
                return None;
            }

            let dx_tan = 2.0 * self.distortion.p1 * x * y + self.distortion.p2 * (r2 + 2.0 * x * x);
            let dy_tan = self.distortion.p1 * (r2 + 2.0 * y * y) + 2.0 * self.distortion.p2 * x * y;
            let x_next = (xd[0] - dx_tan) / radial;
            let y_next = (xd[1] - dy_tan) / radial;

            if !x_next.is_finite() || !y_next.is_finite() {
                return None;
            }

            let dx = x_next - x;
            let dy = y_next - y;
            x = x_next;
            y = y_next;

            if (dx * dx + dy * dy).sqrt() <= cfg.eps.max(0.0) {
                break;
            }
        }

        let out = self.intrinsics.normalized_to_pixel([x, y]);
        if out[0].is_finite() && out[1].is_finite() {
            Some(out)
        } else {
            None
        }
    }
}

impl PixelMapper for CameraModel {
    fn image_to_working_pixel(&self, image_xy: [f64; 2]) -> Option<[f64; 2]> {
        self.undistort_pixel(image_xy)
    }

    fn working_to_image_pixel(&self, working_xy: [f64; 2]) -> Option<[f64; 2]> {
        self.distort_pixel(working_xy)
    }
}

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

    fn sample_camera() -> CameraModel {
        CameraModel {
            intrinsics: CameraIntrinsics {
                fx: 900.0,
                fy: 920.0,
                cx: 640.0,
                cy: 480.0,
            },
            distortion: RadialTangentialDistortion {
                k1: -0.12,
                k2: 0.03,
                p1: 0.001,
                p2: -0.0008,
                k3: 0.0,
            },
        }
    }

    #[test]
    fn intrinsics_validation_rejects_zero_focal() {
        let k = CameraIntrinsics {
            fx: 0.0,
            fy: 500.0,
            cx: 0.0,
            cy: 0.0,
        };
        assert!(!k.is_valid());
        assert!(k.pixel_to_normalized([100.0, 100.0]).is_none());
    }

    #[test]
    fn zero_distortion_roundtrip_is_exact() {
        let cam = CameraModel {
            intrinsics: CameraIntrinsics {
                fx: 800.0,
                fy: 820.0,
                cx: 640.0,
                cy: 480.0,
            },
            distortion: RadialTangentialDistortion::default(),
        };
        let p = [300.25, 210.75];
        let d = cam.distort_pixel(p).unwrap();
        let u = cam.undistort_pixel(d).unwrap();
        assert!((u[0] - p[0]).abs() < 1e-12);
        assert!((u[1] - p[1]).abs() < 1e-12);
    }

    #[test]
    fn roundtrip_with_distortion_is_stable() {
        let cam = sample_camera();
        let p = [250.0, 180.0];
        let d = cam.distort_pixel(p).unwrap();
        let u = cam.undistort_pixel(d).unwrap();
        assert!((u[0] - p[0]).abs() < 1e-5, "x={}, p={}", u[0], p[0]);
        assert!((u[1] - p[1]).abs() < 1e-5, "y={}, p={}", u[1], p[1]);
    }
}