mex codegen issue: Class insfilterNonholonomic is not supported by coder.Type as it is a handle class.

Dear Matlab community,

I have a function (see attachment) that I would like to compile to c++ to increase performance and I am following this tutorial. When I run

load('KFmex_data.mat');
codegen -report KFmex.m -args {KF,t_imu,Accel,Gyro,t_gnss,Pos,Vel,Rpos,Rvel,GNSS_step} -test -test;

I get the following error:

Function input at args{1} does not have a valid type.

Caused by:

Class insfilterNonholonomic is not supported by coder.Type as it is a handle class.

Use help codegen for more information on using this command.

Error using codegen

However, according to the documentation of insfilterNonholonomic, this should be fully supported. What am I doing wrong here? Is this a bug?

Any kind of help is much appreciated!

Answer 1

[Gargi Patil]

Hi,

Code generation does not support handle class objects as entry point arguments. You can refer to the linked documentation for more information. Therefore, insfilterNonholonomic objects can not be passed as inputs to a code generation function.

However, the code generation support indicated in the documentation of insfilterNonholonomic allows usage of its objects within the function as follows:

function [state,covariance,stddev] = KFmex(t_imu,Accel,Gyro,t_gnss,Pos,Vel,Rpos,Rvel,GNSS_step) %#codegen
%%KF as an arugment has been removed

KF = insfilterNonholonomic;  %Example 
%%Code generation will not throw an error

j = 1;
k = 1;
...
end

Kindly note that loading the variable KF within the function using the load command is not viiable for the same reason as above.

[fixusc]

Generally, I can get this to work now, thanks!

I have still a small issue I don't know how to deal with properly:

I want to set the property 'ReferenceFrame' of the insfilterNonholonomic to 'ENU' (the default is 'NED'). However, Matlab coder tells me that this (nontunable) property needs to be set to a constant value. What even is a constant value in Matlab and how can I achieve this? I have tried to define a class with a constant property with the value 'ENU'

classdef ENU
   properties (Constant)
      ReferenceFrame = 'ENU';
   end
end

and assigning the value to the filter object by using

KF.ReferenceFrame = ENU.ReferenceFrame;

but it doesn't work and gives the same error as when I specify it as

KF.ReferenceFrame = 'ENU';

This is the full error message:

??? Failed to compute constant value for nontunable property 'ReferenceFrame'. In code generation, nontunable properties can only be assigned constant values.

[fixusc]

I got it to work by passing the variable as a constat when calling Matlab coder:

codegen -report KFmex.m -args {t_imu,Accel,Gyro,t_gnss,Pos,Vel,Rpos,Rvel,GNSS_step,IMUSampleRate,coder.Constant(ReferenceFrame),ReferenceLocation,DecimationFactor,State,StateCovariance,GyroscopeNoise,AccelerometerNoise,GyroscopeBiasNoise,GyroscopeBiasDecayFactor,AccelerometerBiasNoise,AccelerometerBiasDecayFactor,ZeroVelocityConstraintNoise}

The relevant part of the command above is:

... { ... coder.Constant(ReferenceFrame) ... } ...