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Add ego bodies to capsule list

Since R2020b



addEgo(capsuleListObj,egoStruct) adds one or more ego bodies to the 2-D dynamic capsule list with the specified ID, state, and geometry values given in egoStruct.

status = addEgo(capsuleListObj,egoStruct) additionally returns an indicator of whether each specified ego body was added, updated, or a duplicate.


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Build an ego body path and maintain obstacle states using the dynamicCapsuleList object. Visualize the states of all objects in the environment at different timestamps. Validate the path of the ego body by checking for collisions with obstacles in the environment.

Create the dynamicCapsuleList object. Extract the maximum number of steps to use as the number of time stamps for your object paths.

obsList = dynamicCapsuleList;
numSteps = obsList.MaxNumSteps;

Add Ego Body

Define an ego body by specifying the ID, geometry, and state together in a structure. The capsule geometry has a length of 3 m and radius of 1 m. Specify the state as a linear path from x = 0m to x = 100m.

egoID1 = 1;
geom = struct("Length",3,"Radius",1,"FixedTransform",eye(3));
states = linspace(0,1,obsList.MaxNumSteps)'.*[100 0 0];

egoCapsule1 = struct('ID',egoID1,'States',states,'Geometry',geom);

ylim([-20 20])

Add Obstacles

Specify states for two obstacles that are separated from the ego body by 5 m in opposite directions on the y-axis.. Assume the obstacles have the same geometry geom as the ego body.

obsState1 = states + [0 5 0];
obsState2 = states + [0 -5 0];

obsCapsule1 = struct('ID',1,'States',obsState1,'Geometry',geom);
obsCapsule2 = struct('ID',2,'States',obsState2,'Geometry',geom);


ylim([-20 20])

Update Obstacles

Alter your obstacle locations and geometry dimensions over time. Use the previously generated structure, modify the fields, and update the obstacles using the updateObstacleGeometry and updateObstaclePose object functions. Reduces the radius of the first obstacle to 0.5 m, and change the path to move it towards the ego body.

obsCapsule1.Geometry.Radius = 0.5;

obsCapsule1.States = ...
    [linspace(0,100,numSteps)' ... % x
     linspace(5,-4,numSteps)' ... % y 
     zeros(numSteps,1)]; % theta


Check for Collisions

Visualize the new paths. Show where collisions between the ego body and an obstacle, which the display highlights in red. Notice that collisions between the obstacles are not checked.

ylim([-20 20])
xlabel("X (m)")
ylabel("Y (m)")

Programmatically check for collisions by using the checkCollision object function. The function returns a vector of logical values that indicates the status of each time step. The vector is transposed for display purposes.

collisions = checkCollision(obsList)'
collisions = 1x31 logical array

   0   0   0   0   0   0   0   0   0   0   0   0   1   1   1   1   1   1   1   1   1   1   0   0   0   0   0   0   0   0   0

To validate paths with a large number of steps, use the any function on the vector of collision values.

if any(collisions)
    disp("Collision detected.")
Collision detected.

Update Ego Path

Specify a new path for the ego body. Visualize the paths again, displaying collisions.

egoCapsule1.States = ...
    [linspace(0,100,numSteps)' ... % x
    3*sin(linspace(0,2*pi,numSteps))' ... % y
    zeros(numSteps,1)]; % theta


ylim([-20 20])

Input Arguments

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Dynamic capsule list, specified as a dynamicCapsuleList object.

Ego body parameters, specified as an N-element structure or a structure array, where N is the number of added ego bodies. The fields of each structure define the ID, geometry, and states of an ego body:

  • ID –– Integer that identifies each object. Stored in the EgoIDs property of the dynamicCapsuleList object specified by the capsuleListObj argument.

  • States –– Location and orientation of the object as an M-by-3 matrix, where each row is of form [x y theta], and M is the number of states for the specified ego body in the world frame. The list of states assumes each state is separated by a fixed time interval. xy-positions are in meters and theta is in radians.

  • Geometry –– Structure with fields Length, Radius, and FixedTransform. These fields define the size of the capsule-based object using the specified length for the cylinder and semicircle radius for the end caps. To shift the capsule geometry from the default origin, specify the FixedTransform field as a fixed transform relative to the local frame of the capsule. To keep the default capsule origin, specify the transform as eye(3).

Capsule geometry image showing the position and orientation of the capsule dimensions. Positive X is the right direction in the world frame. Positive Y is up. Positive theta is a counter-clockwise rotation from the world frame. The capsule geometry has a radius for the circular ends and a length for the rectangular section in the middle.

Output Arguments

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Result of adding ego bodies, returned as a N-element column vector of ones, zeros, and negative ones. N is the number of ego bodies specified in the egoStruct argument. Each value indicates whether the associated body is added (1), updated (0), or a duplicate (-1). While adding ego bodies, if multiple structures with the same body ID are found in the structure array egoStruct, then the function marks the previous entry as duplicate and ignores it.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2020b