Regionprops function in Simulink

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Emmet Brown
Emmet Brown 2016-9-24
评论： Walter Roberson 2019-5-26
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:
  1 个评论
Fernando Camacho Villalobos
Fernando Camacho Villalobos 2019-5-26
Hi! Did you solve this problem? I need to create the same block for Simulink. Help me, please.

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Walter Roberson
Walter Roberson 2016-9-25
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.
  1 个评论
Walter Roberson
Walter Roberson 2019-5-26
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.

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