isMotionValid

Class: nav.StateValidator
Namespace: nav

Check if path between states is valid

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Syntax

[isValid,lastValid] = isMotionValid(validatorObj,state1,state2)

Description

[isValid,lastValid] = isMotionValid(validatorObj,state1,state2) determines if the motion between two states is valid by interpolating between states. The function also returns the last valid state along the path.

A default implementation for this method is provided when you call createPlanningTemplate.

example

Input Arguments

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State validator object, specified as an object from a subclass of nav.StateValidator. For provided state validator objects, see validatorOccupancyMap or validatorVehicleCostmap.

Initial state position, specified as a n-element vector or m-by-n matrix of row vectors. n is the dimension of the state space specified in the state space property in validatorObj.

Final state position, specified as a n-element vector or m-by-n matrix of row vectors. n is the dimension of the state space specified in the state space property in validatorObj.

Output Arguments

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Valid states, specified as a m-element vector of 1s and 0s.

Data Types: logical

Final valid state along path, specified as a n-element vector. n is the dimension of the state space specified in the state space property in validatorObj.

Examples

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Open Live Script

This example shows how to use the createPlanningTemplate function to generate a template for customizing your own state validation class. State validation is used with path planning algorithms to ensure valid paths. The template function provides a basic implementation for example purposes.

Call the create template function. This function generates a class definition file for you to modify for your own implementation. Save this file.

createPlanningTemplate("StateValidator")

Class and Property Definition

The first part of the template specifies the class definition and any properties for the class. Derive from the nav.StateValidator class. You can specify any additional user-defined properties here.

classdef MyCustomStateValidator < nav.StateValidator & ...
        matlabshared.planning.internal.EnforceScalarHandle
    properties
       % User-defined properties
    end

Save your custom state validator class and ensure your file name matches the class name.

Class Constructor

Use the constructor to set the name of the state space validator and specify the state space object. Set a default value for the state space if one is not provided. Call the constructor of the base class. Initialize any other user-defined properties. This example uses a default of MyCustomStateSpace, which was illustrated in the previous example.

methods
        function obj = MyCustomStateValidator(space)
            narginchk(0,1)
            
            if nargin == 0
                space = MyCustomStateSpace;
            end

            obj@nav.StateValidator(space);
            
           % Initialize user-defined properties
        end

Copy Semantics

Specify the copy method definition. Copy all the values of your user-defined variables into a new object, so copyObj is a deep copy. The default behavior given in this example creates a new copy of the object with the same type.

        function copyObj = copy(obj)
            copyObj = feval(class(obj), obj.StateSpace);
        end

Check State Validity

Define how a given state is validated. The state input can either be a single row vector, or a matrix of row vectors for multiple states. Customize this function for any special validation behavior for your state space like collision checking against obstacles.

        function isValid = isStateValid(obj, state) 
            narginchk(2,2);
            nav.internal.validation.validateStateMatrix(state, nan, obj.StateSpace.NumStateVariables, ...
                "isStateValid", "state");
            
            bounds = obj.StateSpace.StateBounds';
            inBounds = state >= bounds(1,:) & state <= bounds(2,:);
            isValid = all(inBounds, 2);
            
        end

Check Motion Validity

Define how to generate the motion between states and determine if it is valid. For this example, use linspace to evenly interpolate between states and check if these states are valid using isStateValid. Customize this function to sample between states or consider other analytical methods for determining if a vehicle can move between given states. 

        function [isValid, lastValid] = isMotionValid(obj, state1, state2)
            narginchk(3,3);
            state1 = nav.internal.validation.validateStateVector(state1, ...
                obj.StateSpace.NumStateVariables, "isMotionValid", "state1");
            state2 = nav.internal.validation.validateStateVector(state2, ...
                obj.StateSpace.NumStateVariables, "isMotionValid", "state2");
            
            if (~obj.isStateValid(state1))
                error("statevalidator:StartStateInvalid", "The start state of the motion is invalid.");
            end
            
            % Interpolate at a fixed interval between states and check state validity
            numInterpPoints = 100;
            interpStates = obj.StateSpace.interpolate(state1, state2, linspace(0,1,numInterpPoints));
            interpValid = obj.isStateValid(interpStates);
            
            % Look for invalid states. Set lastValid state to index-1.
            firstInvalidIdx = find(~interpValid, 1);
            if isempty(firstInvalidIdx)
                isValid = true;
                lastValid = state2;
            else
                isValid = false;
                lastValid = interpStates(firstInvalidIdx-1,:);
            end
            
        end

Terminate the methods and class sections.

    end
end

Save your state space validator class definition. You can now use the class constructor to create an object for validation of states for a given state space.

Version History

Introduced in R2019b

See Also

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