### Intersections of Lines, Segments and Planes (2D & 3D)

In Euclidean geometry, the intersection of a line and a line can be the empty set, a point, or a line. Distinguishing these cases and finding the intersection point have use, for example, in computer graphics, motion planning, and collision detection. In three-dimensional Euclidean geometry, if two lines are not in the same A necessary condition for two lines to intersect is. When straight lines intersect on a two-dimensional graph, they meet at only one point, represent are curved, so they can intersect a straight line at 0, 1, or 2 points. . Once you've set one side equal to zero, there are three ways to solve a . If you're asking for help learning/understanding something mathematical, post in the Simple Questions thread or /r/learnmath. I was listening to Tessellate by alt-J yesterday and thinking about the line "triangles are my favorite shape: three points where two lines meet.".

If both lines are segments, then both solution parameters, sI and tI, must be in the [0,1] interval for the segments to intersect. Plane Intersections Planes are represented as described in Algorithm 4, see Planes.

### Three Points Where Two Lines Meet : math

Let L be given by the parametric equation: If this is true, then L and P are parallel and either never intersect or else L lies totally in the plane P. Disjointness or coincidence can be determined by testing whether any one specific point of L, say P0, is contained in Pthat is whether it satisfies the implicit line equation: At the intersect point, the vector is perpendicular to n, where.

This is equivalent to the dot product condition: If the line L is a finite segment from P0 to P1, then one just has to check that to verify that there is an intersection between the segment and the plane. For a positive ray, there is an intersection with the plane when.

Intersection of 2 Planes In 3D, two planes P1 and P2 are either parallel or they intersect in a single straight line L.

### Intersection of Two Lines | Zona Land Education

The planes P1 and P2 are parallel whenever their normal vectors n1 and n2 are parallel, and this is equivalent to the condition that: In software, one would test if where division by would cause overflow, and uses this as the robust condition for n1 and n2 to be parallel in practice. When not parallel, is a direction vector for the intersection line L since u is perpendicular to both n1 and n2, and thus is parallel to both planes as shown in the following diagram.

That is, we need to find a point that lies in both planes. We can do this by finding a common solution of the implicit equations for P1 and P2. But there are only two equations in the 3 unknowns since the point P0 can lie anywhere on the 1-dimensional line L.

So we need another constraint to solve for a specific P0. There are a number of ways this could be done: A Direct Linear Equation.

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This is will be true when the z-coordinate uz of is nonzero. So, one must first select a nonzero coordinate of u, and then set the corresponding coordinate of P0 to 0.

Further, one should choose the coordinate with the largest absolute value, as this will give the most robust computations. Suppose thatthen lies on L. Solving the two equations: The denominator here is equal to the non-zero 3rd coordinate of u. B Line Intersect Point. If one knows a specific line in one plane for example, two points in the planeand this line intersects the other plane, then its point of intersection, I, will lie in both planes.

Thus, it is on the line of intersection for the two planes, and the parametric equation of L is: One way of constructing a line in one plane that must intersect the other plane is to project one plane's normal vector onto the other plane.

This gives a line that must always be orthogonal to the line of the planes' intersection. So, the projection of n2 on P1 defines a line that intersects P2 in the sought for point P0 on L.

## Geometry for Elementary School/Lines

Then the projected line in P1 is L1: C 3 Plane Intersect Point. This always works since: If the denominator and numerator for the equations for ua and ub are 0 then the two lines are coincident.

The equations apply to lines, if the intersection of line segments is required then it is only necessary to test if ua and ub lie between 0 and 1. Whichever one lies within that range then the corresponding line segment contains the intersection point.

## MODERATORS

If both lie within the range of 0 to 1 then the intersection point is within both line segments. C version for Rockbox firmware by Karl Kurbjun. C version by Olaf Rabbachin. VBA implementation by Giuseppe Iaria. Javascript version by Leo Bottaro. The shortest line between two lines in 3D Written by Paul Bourke April Two lines in 3 dimensions generally don't intersect at a point, they may be parallel no intersections or they may be coincident infinite intersections but most often only their projection onto a plane intersect.

When they don't exactly intersect at a point they can be connected by a line segment, the shortest line segment is unique and is often considered to be their intersection in 3D. The following will show how to compute this shortest line segment that joins two lines in 3D, it will as a bi-product identify parallel lines.