# checkCollision

Check if two geometries are in collision

Since R2019b

## Description

collisionStatus = checkCollision(geom1,geom2) returns the collision status between the two convex geometries geom1 and geom2. If the two geometries are in collision at their specified poses, collisionStatus is 1. If the function does not find a collision, collisionStatus is 0.

example

[collisionStatus,sepdist,witnesspts] = checkCollision(geom1,geom2) returns the minimal distance sepdist and witness points witnesspts of each geometry when the function does not find a collision between the two geometries.

## Examples

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This example shows how to check the collision status of two collision geometries.

Create a box collision geometry.

bx = collisionBox(1,2,3);

Create a cylinder collision geometry.

cy = collisionCylinder(3,1);

Translate the cylinder along the x-axis by 2.

T = trvec2tform([2 0 0]);
cy.Pose = T;

Plot the two geometries.

show(cy)
hold on
show(bx)
xlim([-5 5])
ylim([-5 5])
zlim([-5 5])
hold off

Check the collision status. Confirm the status is consistent with the plot.

[areIntersecting,dist,witnessPoints] = checkCollision(bx,cy)
areIntersecting = 1
dist = NaN
witnessPoints = 3×2

NaN   NaN
NaN   NaN
NaN   NaN

Translate the box along the x-axis by 3 and down the z-axis by 4. Confirm the box and cylinder are not colliding.

T = trvec2tform([0 3 -4]);
bx.Pose = T;
[areIntersecting,dist,witnessPoints] = checkCollision(bx,cy)
areIntersecting = 0
dist = 2
witnessPoints = 3×2

0.4286    0.4286
2.0000    2.0000
-2.5000   -0.5000

Plot the box, cylinder, and the line segment representing the minimum distance between the two geometries.

show(cy)
hold on
show(bx)
wp = witnessPoints;
plot3([wp(1,1) wp(1,2)], [wp(2,1) wp(2,2)], [wp(3,1) wp(3,2)], 'bo-')
xlim([-5 5])
ylim([-5 5])
zlim([-5 5])
hold off

Create two collision capsules. Center one at the origin, and set the pose of the other capsule to 3 meters away from the origin on the y-axis. Display the capsules.

cc1 = collisionCapsule(1,4);
cc2 = collisionCapsule(1,4);
cc2.Pose = trvec2tform([0 3 0]);
show(cc1);
hold on
show(cc2);
axis auto
hold off

Check for collision between the two collision capsules. Because they are not visually colliding, the function should return real-valued separation distances and witness points. Display the separation distances and witness points.

[isColliding,separationDist,witnessPts] = checkCollision(cc1,cc2);
disp("Separation Distance: " + num2str(separationDist))
Separation Distance: 1
disp("Capsule 1 Witness Point (X Y Z): " + num2str(witnessPts(:,1)'))
Capsule 1 Witness Point (X Y Z): 0  1 -2
disp("Capsule 2 Witness Point (X Y Z): " + num2str(witnessPts(:,2)'))
Capsule 2 Witness Point (X Y Z): 0  2 -2

Rotate the second capsule 90 degrees on the z-axis.

cc2.Pose(1:3,1:3) = eul2rotm([0 0 pi/2]);
show(cc1);
hold on
show(cc2);
axis auto

Check again for collision between the capsules. Because they are in collision, the function returns the separation distance and witness points as NaN.

[isColliding,separationDist,witnessPts] = checkCollision(cc1,cc2);
disp("Separation Distance: " + num2str(separationDist))
Separation Distance: NaN
disp("Capsule 1 Witness Point (X Y Z): " + num2str(witnessPts(:,1)'))
Capsule 1 Witness Point (X Y Z): NaN  NaN  NaN
disp("Capsule 2 Witness Point (X Y Z): " + num2str(witnessPts(:,2)'))
Capsule 2 Witness Point (X Y Z): NaN  NaN  NaN

## Input Arguments

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First collision geometry, specified as one of these collision geometry objects:

Collision geometry, specified as one of these collision geometry objects:

## Output Arguments

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Collision status, returned as 0 or 1. If the two geometries are in collision, collisionStatus is 1. Otherwise, the value is 0.

Data Types: double

Minimal distance between the two collision geometries, returned as a real number. The line segment that connects the witness points witnesspts determines the minimal distance between the two geometries. When the two geometries are in collision, sepdist is NaN.

Data Types: double

Witness points on each geometry, returned as a 3-by-2 matrix. Each column is the location of the witness point on the corresponding geometry, geom1 or geom2. The line segment that connects the two witness points has length septdist. When the two geometries are in collision, every element of witnesspts is NaN.

Data Types: double

## Limitations

• Collision checking results are unreliable when the minimal distance is below 10-5 m.

## References

[1] Gilbert, E.G., D.W. Johnson, and S.S. Keerthi. "A fast procedure for computing the distance between complex objects in three-dimensional space." IEEE Journal on Robotics and Automation 4, no. 2 (April 1988): 193–203. https://doi.org/10.1109/56.2083.

## Version History

Introduced in R2019b