Ray Line Intersection

Decoding the Intersection: A Comprehensive Guide to Ray Line Intersection

Imagine you're designing a self-driving car. A crucial aspect of its navigation system involves precisely determining the location of obstacles. The car's sensors emit rays (essentially, lines extending from a point in a single direction), and the system needs to calculate where these rays intersect with the boundaries of objects represented as lines. This is the essence of ray-line intersection – a fundamental problem in computer graphics, robotics, and many other fields. This article delves into the mathematics and practical applications of this critical calculation, providing you with a solid understanding of the underlying principles and techniques.

1. Defining the Problem: Rays and Lines

Before diving into the calculations, let's clearly define our terms. A ray is a half-line; a line segment that extends infinitely in one direction from a starting point (origin). We can represent a ray mathematically using a parametric equation:

R(t) = O + tD, where t ≥ 0

O is the origin vector (x, y) of the ray.
D is the direction vector (dx, dy), a unit vector pointing along the ray's direction.
t is a scalar parameter controlling the distance along the ray. Since t ≥ 0, the ray only extends in one direction.

A line, on the other hand, extends infinitely in both directions. Its equation can be represented as:

L(s) = P + sV

P is a point on the line (x, y).
V is the direction vector (vx, vy) of the line.
s is a scalar parameter, which can be any real number (positive, negative, or zero).

The goal of ray-line intersection is to find the point where the ray R(t) and the line L(s) intersect, if such a point exists.

2. Calculating the Intersection Point

To find the intersection, we need to solve for the values of `t` and `s` that satisfy both the ray and line equations simultaneously:

O + tD = P + sV

This vector equation can be broken down into two scalar equations (one for the x-coordinates and one for the y-coordinates):

Ox + tDx = Px + sVx
Oy + tDy = Py + sVy

We now have a system of two linear equations with two unknowns (t and s). Several methods can be used to solve this system, including substitution or matrix methods. A common approach involves solving for `t` using Cramer's rule or a similar technique. If a solution for `t` exists and `t ≥ 0`, then an intersection occurs. The intersection point can then be calculated by substituting the value of `t` back into the ray equation:

Intersection Point = O + tD

If `t < 0`, the intersection occurs on the line but behind the ray's origin, so no intersection is considered to have occurred from the perspective of the ray. If no solution for `t` and `s` exists, the ray and line are parallel and do not intersect.

3. Handling Special Cases and Robustness

The above method works well in most scenarios, but we need to consider special cases. If `DxVy - DyVx` (the determinant of the system of equations) is zero, the lines are parallel and no intersection exists. Furthermore, numerical inaccuracies can arise in calculations. Robust implementations often incorporate tolerance checks to handle near-parallel lines or near-zero determinant situations.

4. Real-World Applications

Ray-line intersection is a cornerstone in various fields:

Computer Graphics: Ray tracing algorithms utilize this to determine which objects are visible from a given viewpoint. Each ray represents a light path, and intersections determine what surfaces the light interacts with.
Robotics: Autonomous navigation systems use ray-line intersection to detect obstacles in a robot's path. Sensor data (like lidar) generates rays, and intersection calculations help create a map of the environment.
Collision Detection: In game development and simulations, ray-line intersection helps detect collisions between objects. This is especially useful for handling complex shapes approximated by lines and polygons.
Geographic Information Systems (GIS): Determining the intersection of a line feature (a road, river) with a ray representing a sensor's range is essential in various geographic analyses.

5. Practical Implementation Considerations

Implementing ray-line intersection requires careful consideration of numerical stability and efficiency. Using appropriate data structures (like vectors) and optimized algorithms can significantly improve performance, especially when dealing with a large number of rays and lines. Libraries like NumPy (Python) or similar linear algebra packages can simplify the calculations and improve accuracy.

Conclusion

Ray-line intersection, while conceptually simple, plays a pivotal role in numerous applications. Understanding its underlying mathematics and potential challenges is crucial for developing robust and efficient solutions. The careful consideration of special cases and the application of efficient numerical methods are essential for successful implementation in real-world scenarios.

FAQs

1. What happens if the ray and line are parallel? If the lines are parallel, there is no intersection. The determinant of the coefficient matrix in the system of equations will be zero.

2. How can I handle floating-point inaccuracies in the calculations? Introduce a tolerance threshold (a small value like 1e-6) to account for near-zero values when checking for intersection or parallelism.

3. What are the computational complexities of ray-line intersection? The algorithm is relatively simple and has a constant-time complexity O(1), making it computationally inexpensive for single intersection calculations.

4. Can this method be extended to 3D? Yes, the principle can be extended to 3D, requiring a system of three equations with three unknowns (for the intersection of a ray and a plane, a common 3D analogue).

5. Are there any alternative methods for detecting ray-line intersections? While the parametric equation approach is common, other methods exist, including using cross products for determining coplanarity in 3D. The choice depends on the specific application and efficiency requirements.

Search Results:

Lecture 15: Ray Polygon Intersection - Colorado State University Ray / Polygon Intersection • Given t, we know the point where the ray intersects the plane of the polygon P = L + tU • But is it inside the polygon? • For the convex case see the Sage Notebook. – Mostly omitted from this slide deck. • For non-convex learn the odd-even rule – Covered in the remainder of this slide deck.

algorithms - How to determine if 2 rays intersect? - Computational ... 3 Dec 2020 · All you need to do is to present these two straight lines as a set of points (x,y) depending on the parameter which is the length along the line. Then finding the intersection boils down to solving a small linear system, and from the determinant of it …

algorithm - Determining if two rays intersect - Stack Overflow 13 Oct 2016 · I want to find out if the two rays intersect, but I don't need to know where they intersect (it's part of a collision detection algorithm). Everything I have looked at so far describes finding the intersection point of two lines or line segments. Is there a fast algorithm to solve this?

Ray Tracing (Intersection) - Department of Computer Science Ray intersection in software • Scenes usually have many objects • Need to ﬁnd the ﬁrst intersection along the ray – that is, the one with the smallest positive t value • Loop over objects – ignore those that don’t intersect – keep track of the closest seen so far – Convenient to give rays an ending t value for this purpose (then

Math Notes: Ray-Plane Intersection - Sam Symons 17 Aug 2017 · A ray is built atop vectors. It is a point in space, with a direction; think of a ray as a semi-infinite line. In ray tracing, you might think of a ray as the line-of-sight from your camera, where the origin is the location of your lens and the direction is the way your camera is facing.

Intersection of a Ray and a Line Segment in 3D – CodeFull 12 Mar 2016 · Given a ray (with a start point, an end point and direction) and a line segment with the defined start and end points, we perform the 3D line intersection test.

A Trig-less Line of Sight Algorithm in Two Dimensions - GitHub … We want to figure out where (if anywhere) a given ray and a given line segment intersect. Checking rays for intersections is commonly known as raycasting, although this term is most commonly associated with its use in 3D graphics for determining which objects should be visible to a camera. Nonetheless, the principle is the same.

6.4: Intersection of Straight Lines - Mathematics LibreTexts Finding an intersection of two lines graphically is not always easy or practical; therefore, we will now learn to solve these problems algebraically. At the point where two lines intersect, the $x$ and $y$ values for both lines are the same. So in order to find the intersection, we either let the $x$-values or the $y$-values equal.

Ray-Object Intersection for Planes, Spheres, and Quadrics Ray-Object Intersection in General Given a function f(P), we can raytrace the 3D surface f(P)=0 by plugging in the ray equation for P, and then solving f(C+t*D)=0 for t. Once we find a point on the surface, we can compute surface normals from the gradient of f.

Advanced Computer Graphics Ray-Object Intersections - uni … An intersection occurs, if a point on a ray satisfies the implicit equation E.g., all points p on a plane with surface normal n and offset r satisfy the equation The intersection with a ray can be computed based on t if d is not orthogonal to n

How to calculate ray-line segment intersection preferably in OpenCV ... 22 Dec 2018 · I have 4 lines segment, A, B, C and D. Each line is represented as two points. Eg. line A is represented as point A1 and point A2. What I want is . point X, which is the point where line A ray intersect with line B; distance between X and A1(origin) When testing for intersection, line A ray should not. intersect with line segment D

How do you check for intersection between a line segment and a line ray ... To find the point of intersection, you can use the following system of equations and solve for xp and yp, where lb and rb are the y-intercepts of the line segment and the ray, respectively. y1=(y2-y1)/(x2-x1)*x1+lb yp=(y2-y1)/(x2-x1)*xp+lb y=sin(theta)/cos(theta)*x+rb yp=sin(theta)/cos(theta)*x+rb

Math: line intersections - Kelvin van Hoorn 11 May 2021 · Lately a lot of my shaders have used a bit of raymarching, where I primarily rely on finding the intersections between a line (ray) and a shape. In this post I will go over the general approach for calculating these intersections and provide a list of HLSL implementations.

Ray Tracing 1: The Basics - Stanford University Light rays travel from the light sources to the eye (but the physics is invariant under path reversal - reciprocity). Shooting rays to determine whether a surface is visible from a light source. The plane is all points p’, where p’- p is orthogonal to n. Want t where the ray intersects the plane... What About Rays Parallel to a Plane?

How to find out if a ray intersects a rectangle? 6 Jun 2012 · So for each side of the rectangle, find the intersection (if any) of the line passing through the endpoints with the ray AB; then it's simply a range check to determine if that intersection lies is part of the line segment on the boundary of the rectangle, or if it is outside.

Ray Tracing: intersection and shading - Department of Computer … Ray tracer architecture 101 • You want a class called Ray – point and direction; evaluate(t) – possible: tMin, tMax • Some things can be intersected with rays – individual surfaces – groups of surfaces (acceleration goes here) – the whole scene

c++ - How to calculate a ray plane intersection - Stack Overflow The ray-plane intersection occurs when q satisfies the plane equation. Substituting, we have: = -dot(n, p + t * v) = -dot(n, p) + t * dot(n, v) This value of t can be used to determine the intersection by plugging it back into p + t*v.

Line-Torus Intersection for Ray Tracing: Alternative Formulations Intersection of a line or ray with a surface is the key problem solved in all ray-tracing techniques. Due to the computational complexity a bounding volumes are used to detect cases when a line cannot intersect the given object.

Ray × scene intersections - Computer Graphics Group set operations are performed in the 1D ray-space: – distributivity: P (A-B) = (P A) - (P B) – general ray-scene intersection is a collection of line segments (intervals in 1D ray-space) geometric transformations: – inverse transformation applied to a ray

Collision/Intersection of (2D) Ray to Line Segment 14 Oct 2014 · You can do this just by calculating the dot product of the ray vector and the normal. If the result is negative, than this is the normal you are looking for. For example: Vector2 ray; ray = r1 - r0; float result; //if result < 0 than the norm0 is the correct normal result = ray.X * norm0.X + ray.Y * norm0.Y;

geometry - How to determine if a ray intersects a line? 6 Oct 2017 · A simple way to proceed is to find the intersection $Q$ of the two lines and then compare the direction of $Q-O$ to $\mathbf v$. Working in homogeneous coordinates, $\overline{P_1P_2}$ is $\mathbf l=(x_1,y_1,1)\times(x_2,y_2,1)$ and the line that contains the ray is $\mathbf m=(x_0,y_0,1)\times(x_v,y_v,0)$.