Check Collision

R2026b

Check if two convex collision geometries are in collision

Since R2025a

• 

check collision block block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Robotics System Toolbox / Collision Detection

Description

The Check Collision block checks for collision between two convex collision geometries and additionally outputs the separation distance and corresponding witness points between the collision geometries.

Examples

Check Collisions Between Geometries

Open the Simulink® model. This model contains all five of the collision geometry blocks in the Collision Detection library and checks for collision between any two of the collision geometries. Note that the Collision Mesh block uses vertices from the exampleMeshVertices MAT file. The model loads the exampleMeshVertices MAT file when you open the model by using the PreLoadFcn callback.

model = "CollisionCheckingBetweenGeometries.slx";
open_system(model)

Simulate the model.

out = sim("CollisionCheckingBetweenGeometries.slx")

out = 
  Simulink.SimulationOutput:

             collStatus: [1x1 timeseries] 
               geom1Idx: [1x1 timeseries] 
               geom2Idx: [1x1 timeseries] 
                logsout: [1x1 Simulink.SimulationData.Dataset] 
                sepDist: [1x1 timeseries] 
                   tout: [101x1 double] 
             witnessPts: [1x1 timeseries] 

     SimulationMetadata: [1x1 Simulink.SimulationMetadata] 
           ErrorMessage: [0x0 char] 

Get data from the simulation output.

collCheckingPairs = [out.geom1Idx.Data out.geom2Idx.Data];
collStatuses = out.collStatus.Data;
sepDistances = out.sepDist.Data;
witnessPoints = out.witnessPts.Data;

Limitations

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

Ports

Input

Geom1 — First collision geometry to check

bus

First collision geometry, specified as a bus created by any of these collision geometry blocks:

• Collision Box

• Collision Capsule

• Collision Cylinder

• Collision Mesh

• Collision Sphere

Geom2 — Second collision geometry to check

bus

Second collision geometry, specified as a bus created by any of these collision geometry blocks:

• Collision Box

• Collision Capsule

• Collision Cylinder

• Collision Mesh

• Collision Sphere

Output

CollStatus — Collision status

scalar

Collision status, returned as a Boolean 0 or 1. If the two geometries are in collision, CollStatus outputs 1. Otherwise, the value is 0.

SepDist — Minimum distance between collision geometries

scalar

Minimum distance between the two collision geometries, returned as a scalar. The line segment that connects the witness points WitnessPts, determines the minimum distance between the two geometries. When the two geometries are in collision, SepDist outputs NaN.

WitnessPts — Witness points on each geometry

matrix

Witness points on each geometry, returned as a 3-by-2 matrix. The first column is the location of the witness point on the geometry Geom1, and the second column is the location of the witness point on the other geometry Geom2. The length of the line segment that connects the two witness points determines the value from the SepDist port. When the two geometries are in collision, every element of WitnessPts is NaN.

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Simulate using — Type of simulation to run

Code generation (default) | Interpreted execution

• Code generation — Simulate model using generated C code. The first time you run a simulation, Simulink generates C code for the block. The block reuses the C code for subsequent simulations, as long as the model does not change.

• Interpreted execution — Simulate model using the MATLAB^® interpreter. For more information, see Interpreted Execution vs. Code Generation (Simulink).

Programmatic Use: Add Block

To add the block programmatically, use the add_block function with one of these library block paths as the source.

"robotslcollision/Check Collision"

Example: add_block("robotslcollision/Check Collision","myModel/myBlock",MakeNameUnique="on")

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

The Check Collision block supports code generation with dynamic memory allocation disabled. For more information about disabling dynamic memory allocation, see Dynamic memory allocation in MATLAB functions (Simulink).

Version History

Introduced in R2025a