Regionprops function in Simulink

Hello. I've problem with using regionprops function in Simulink.

The function 'regionprops' is not supported for standalone code generation.

So I made block with such code

function [x1,y1] = f(In)
coder.extrinsic('regionprops'); 
s = regionprops(In,'centroid');
centroids = cat(1, s.centroid);
x1 = centroids(1,1);
y1 = centroids(1,2);

Now I get error that field with parameters is not exist

Attempt to extract field 'centroid' from 'mxArray'.
line 5, column 20:

[Fernando Camacho Villalobos]

Hi! Did you solve this problem? I need to create the same block for Simulink. Help me, please.

Answer 1

[Walter Roberson]

Before the

s = regionprops(In,'centroid');

line, you need

s = struct('centroid', 0);

This signals to the code generator that the mxArray that is returned from the regionprops call needs to be brought into the workspace.

You might find that you need to use one of the methods of indicating variable sized arrays; see http://www.mathworks.com/help/fixedpoint/ug/defining-variable-size-data-for-code-generation.html since you are expecting multiple centroids back.

Your code seems to collect all of the centroids, but then it appears to only pay attention to the first of them. I do not see the point of collecting them all in that case.

    s = struct('centroid', [0 0]);
    s = regionprops(In,'centroid');
    x1 = s.centroid(1,1);
    y1 = s.centroid(1,2);

You might still need to worry about variable-sized arrays though.

[Walter Roberson]

In cases where you are only paying attention to one region, it might make sense to use tools such as bwareafilt() to filter down to a single region first, so that you can predict the size of the return data from regionprops.