Matlab coder with bwboundries

I am getting an issue trying to compile a simulink block. This block contains a matlab function that uses this function call inside:

B = bwboundaries(BW, 8, 'noholes');

Note that BW is simply a binary image of known size.

When trying to compile, I get an error for the function bwboundries returning an unbounded value:

Computed maximum size of the output of function 'bwboundaries' is not bounded. 
Static memory allocation requires all sizes to be bounded. The computed size is [:? x 1]. 
Function 'bla' (#40.123.153), line 7, column 5:
"bwboundaries(BW, 8, 'noholes')"

This simulink model is intended to run on a Beaglebone Black if that helps.

I've tried to declare the variable size of BW and of B with coder.varsize but it did not help.

Thanks..

[Nikhil Sreekumar]

Hey,

Can you mention how you used the coder.varsize? Was it something like this?

coder.varsize('B', [100 1])

Assuming the number of objects and holes won't go above 100.

Thanks

Nikhil

Answer 1

[Ankit Bhardwaj]

According to the following documentation, code generation for 'bwboundaries' function requires 'conn' and 'options' (i.e. 2nd and 3rd parameter) to be a compile-time constant.

https://www.mathworks.com/help/releases/R2017a/images/ref/bwboundaries.html#bvmx88x-1

If this does not help, please provide a reproduction model and information about the MATLAB version you are using.

[Nikhil Sreekumar]

Hi Ankit,

The issue here seems to be related to the output of the bwboundaries function. Also, the options for bwboundaries are declared at compile time.

B = bwboundaries(BW, 8, 'noholes');

Seems like the number of objects and holes are not calculated, (? x 1), or may want the size to be declared beforehand.

Thanks

Nikhil

[Timo]

Hi Nikhil and others,

I am facing the same issue. Since B is a cell array, the coder.varsize('B', [100 1]) command needs to come after the first call of bwboundaries right? To be sure, as Ankit suggested, I also declared the conn variable with coder.varsize, and all variables that are derived from B afterwards in my code.

To give some context to the code below: I am looking for the pixel coordinates (X,Y) of the edge of the largest Blob detected with bwboundaries. Since I do analysis on a region-of-interest, I have another separate function to return the actual pixel coordinates for given ROI-coordinates. If no feature is detected, I simply return NaNs.

In the model explorer, the variables Xe, Ye are set to be variable size with bounds. I turned dynamic memory allocation off since this code needs to be RT at some point.

Many thanks for your help,

Timo

function [Xe,Ye,qual]  = get_boundary_perim(afterthreshmedian,ROI_pars) %#codegen

coder.varsize('Xe',750);
coder.varsize('Ye',750);
coder.varsize('conn',1,0);
coder.varsize('n',1,0);
coder.varsize('afterthreshmedian',size(ROI_pars.ROI),[0 0]);

conn = 8;
B = bwboundaries(afterthreshmedian,conn);
coder.varsize('B', [100 1],[1 0]);
assert(length(B)<100);

n = length(B);

if ~isempty(B)
    Xetemp = cell(1,n);
    Yetemp = cell(1,n);
    lengths = zeros(1,n);
    for ii = 1:n
        xy = B{ii};
        lengths(ii) = length(xy);
    [Xetemp{ii},Yetemp{ii}] = ROIind2imag(ROI_pars,xy(:,2),xy(:,1));
    end
    qual = true;
    
    [~,ind] = max(lengths);
    Xe = Xetemp{ind};
    Ye = Yetemp{ind};
    
else
    Xe = NaN;
    Ye = NaN;
    qual = false;
end