Move geometry lib to frc971/vision
Going to use for target mapping. Previously used this for 2022 vision.
Signed-off-by: Milind Upadhyay <milind.upadhyay@gmail.com>
Change-Id: Ifd9d13d3f9b0ea1aac42fb6c96ef2a5062b9f637
diff --git a/frc971/vision/geometry.h b/frc971/vision/geometry.h
new file mode 100644
index 0000000..e3527f5
--- /dev/null
+++ b/frc971/vision/geometry.h
@@ -0,0 +1,136 @@
+#ifndef FRC971_VISION_GEOMETRY_H_
+#define FRC971_VISION_GEOMETRY_H_
+
+#include "aos/util/math.h"
+#include "glog/logging.h"
+#include "opencv2/core/types.hpp"
+
+namespace frc971::vision {
+
+// Linear equation in the form y = mx + b
+struct SlopeInterceptLine {
+ double m, b;
+
+ inline SlopeInterceptLine(cv::Point2d p, cv::Point2d q) {
+ if (p.x == q.x) {
+ CHECK_EQ(p.y, q.y) << "Can't fit line to infinite slope";
+
+ // If two identical points were passed in, give the slope 0,
+ // with it passing the point.
+ m = 0.0;
+ } else {
+ m = (p.y - q.y) / (p.x - q.x);
+ }
+ // y = mx + b -> b = y - mx
+ b = p.y - (m * p.x);
+ }
+
+ inline double operator()(double x) const { return (m * x) + b; }
+};
+
+// Linear equation in the form ax + by = c
+struct StdFormLine {
+ public:
+ double a, b, c;
+
+ inline std::optional<cv::Point2d> Intersection(const StdFormLine &l) const {
+ // Use Cramer's rule to solve for the intersection
+ const double denominator = Determinant(a, b, l.a, l.b);
+ const double numerator_x = Determinant(c, b, l.c, l.b);
+ const double numerator_y = Determinant(a, c, l.a, l.c);
+
+ std::optional<cv::Point2d> intersection = std::nullopt;
+ // Return nullopt if the denominator is 0, meaning the same slopes
+ if (denominator != 0) {
+ intersection =
+ cv::Point2d(numerator_x / denominator, numerator_y / denominator);
+ }
+
+ return intersection;
+ }
+
+ private: // Determinant of [[a, b], [c, d]]
+ static inline double Determinant(double a, double b, double c, double d) {
+ return (a * d) - (b * c);
+ }
+};
+
+struct Circle {
+ public:
+ cv::Point2d center;
+ double radius;
+
+ static inline std::optional<Circle> Fit(std::vector<cv::Point2d> points) {
+ CHECK_EQ(points.size(), 3ul);
+ // For the 3 points, we have 3 equations in the form
+ // (x - h)^2 + (y - k)^2 = r^2
+ // Manipulate them to solve for the center and radius
+ // (x1 - h)^2 + (y1 - k)^2 = r^2 ->
+ // x1^2 + h^2 - 2x1h + y1^2 + k^2 - 2y1k = r^2
+ // Also, (x2 - h)^2 + (y2 - k)^2 = r^2
+ // Subtracting these two, we get
+ // x1^2 - x2^2 - 2h(x1 - x2) + y1^2 - y2^2 - 2k(y1 - y2) = 0 ->
+ // h(x1 - x2) + k(y1 - y2) = (-x1^2 + x2^2 - y1^2 + y2^2) / -2
+ // Doing the same with equations 1 and 3, we get the second linear equation
+ // h(x1 - x3) + k(y1 - y3) = (-x1^2 + x3^2 - y1^2 + y3^2) / -2
+ // Now, we can solve for their intersection and find the center
+ const auto l =
+ StdFormLine{points[0].x - points[1].x, points[0].y - points[1].y,
+ (-std::pow(points[0].x, 2) + std::pow(points[1].x, 2) -
+ std::pow(points[0].y, 2) + std::pow(points[1].y, 2)) /
+ -2.0};
+ const auto m =
+ StdFormLine{points[0].x - points[2].x, points[0].y - points[2].y,
+ (-std::pow(points[0].x, 2) + std::pow(points[2].x, 2) -
+ std::pow(points[0].y, 2) + std::pow(points[2].y, 2)) /
+ -2.0};
+ const auto center = l.Intersection(m);
+
+ std::optional<Circle> circle = std::nullopt;
+ if (center) {
+ // Now find the radius
+ const double radius = cv::norm(points[0] - *center);
+ circle = Circle{*center, radius};
+ }
+ return circle;
+ }
+
+ inline double DistanceTo(cv::Point2d p) const {
+ const auto p_prime = TranslateToOrigin(p);
+ // Now, the distance is simply the difference between distance from the
+ // origin to p' and the radius.
+ return std::abs(cv::norm(p_prime) - radius);
+ }
+
+ inline double AngleOf(cv::Point2d p) const {
+ auto p_prime = TranslateToOrigin(p);
+ // Flip the y because y values go downwards.
+ p_prime.y *= -1;
+ return std::atan2(p_prime.y, p_prime.x);
+ }
+
+ // Expects all angles to be from 0 to 2pi
+ // TODO(milind): handle wrapping
+ static inline bool AngleInRange(double theta, double theta_min,
+ double theta_max) {
+ return (
+ (theta >= theta_min && theta <= theta_max) ||
+ (theta_min > theta_max && (theta >= theta_min || theta <= theta_max)));
+ }
+
+ inline bool InAngleRange(cv::Point2d p, double theta_min,
+ double theta_max) const {
+ return AngleInRange(AngleOf(p), theta_min, theta_max);
+ }
+
+ private:
+ // Translate the point on the circle
+ // as if the circle's center is the origin (0,0)
+ inline cv::Point2d TranslateToOrigin(cv::Point2d p) const {
+ return cv::Point2d(p.x - center.x, p.y - center.y);
+ }
+};
+
+} // namespace frc971::vision
+
+#endif // FRC971_VISION_GEOMETRY_H_