MATLAB coder error while using 'rospublisher'

I'm facing the error while using MATLAB coder. The error shows 'Value cannot be displayed because the output of 'coder.ceval' does not have a known type. To display the output, first assign the result to a variable of known type.' , and the error was due to

pub = rospublisher("/path", "geometry_msgs/Point", "DataFormat", "struct");

And below is part of my code:

r = rosrate(10);

pub = rospublisher("/path", "geometry_msgs/Point", "DataFormat", "struct");

% ...

while true
    % Create a new ROS message
    msg = rosmessage(pub);

    msg.Data = struct_target_path;
    % Publish the message
    send(pub, msg);
    waitfor(r);
end

What I want to do is to publish a structure message(struct_target_path) with the topic named "/path".

I have already tried various methods, but all of them didn't work.

Thank you for anyone who can help me to fix it.

Answer 1

[Karthik Reddy Vennapureddy]

Hi JhenMin,

The message struct you are creating in while loop using rosmessage API, is of message type "geometry_msgs/Point". This type has no such field 'Data'. Instead it has fields X, Y and Z. So, it is not allowed to do the following:

msg.Data = struct_target_path;

Instead the below syntax is allowed

msg.X = 10;

Thanks,

Karthik Reddy

[JhenMin Hung]

Thanks for your replying!

While,after modifying the code as you mentioned, the error is still apear.

How can i fix it?

[Karthik Reddy Vennapureddy]

Hi JhenMin,

Could you share the complete script for which you are generating the code, to see if there is any other line of code that could be causing this error.

Thanks,

Karthik Reddy

[JhenMin Hung]

Thank you for your prompt reply.

The following is my complete code.

%#codegen
function pathplanning0727 
% subscribe: segnet_img=>uint8(480,640,3)
% publish:target_path


%==================== subscribe segnet_img ====================

segnet_img_sub =  rossubscriber("/segnet/color_mask","sensor_msgs/Image","DataFormat","struct");           %subscribe the segnet img
ros_msg = rosmessage(segnet_img_sub);
segnet_img = rosReadImage(ros_msg);
segnet_img = im2uint8(segnet_img);

%==================== crop image ====================

segnet_img = im2uint8(segnet_img);
cropped_img = zeros([200 440 1],'uint8');
cropped_img(1:200,1:440,1) = segnet_img(251:450,101:540,3);   

%==================== threshold setting and polybuffer ====================

cropped_img_3 = cropped_img(:,:,1);         % 'blue' channel of RGB-images 
cropped_img_3(cropped_img_3>=50) = uint8(255);    % threshold setting
cropped_img_3(cropped_img_3<49) = uint8(0);
uint8 L
[B,L] = bwboundaries(cropped_img_3);        % get max perimeter
perim = zeros([1 0],'uint8');
for k = 1:1:uint8(size(B,1))
    perim = [perim size(B{k,:},1)];
end
Max_perim = uint8(find(perim == max(perim)));
B1_cell = B{Max_perim,:};
B1 = B1_cell;

Obj_perim_length = size(B1,1);   % perimeter length in pixels
xp = uint8(B1(:,2));                    % x in pixel coordinates
yp = uint8(B1(:,1));                    % y in pixel coordinates
D = zeros(size(segnet_img),'uint8');

for k = 1:1:numel(xp)            % numel(xp):number of units in xp
  D(yp(k),xp(k)) = 1;
end
n_polybuffer1 = uint8(15);
n_polybuffer2 = uint8(-35); 
B1_polyshape = polyshape(B1(:,2)+100,B1(:,1)+250);


pb1 = polybuffer(B1_polyshape,n_polybuffer1);   
pb2 = polybuffer(pb1,n_polybuffer2);
pb2_vertices = double(pb2.Vertices);

[isnan_row, isnan_col] = find(isnan(pb2_vertices));
[n1 n2] = size(isnan_row);     
size_pb2_vertices = size(pb2_vertices);
break_point = zeros((n1/2)+2,1,'uint8');
break_point(1) = uint8(1);
break_point(2:(n1/2)+1) = uint8(isnan_row(1:n1/2));
break_point((n1/2)+2) = uint8(size_pb2_vertices(1,1));

area = zeros([1 2],'uint8');
area_size = zeros(0,'uint8');

for i_1 = 1:(n1/2)+1
    pb2_vertices_a = uint8(break_point(i_1));
    pb2_vertices_b = uint8(break_point(i_1+1)-1);
    area_a = uint8(2*i_1-1);
    area_b = uint8(2*i_1);
    area(pb2_vertices_a:pb2_vertices_b,area_a:area_b) = pb2_vertices(pb2_vertices_a:pb2_vertices_b,:);    
    area_size(i_1) = pb2_vertices_b;                         
end

area_size_top = uint8(maxk(area_size,1));
selected_area = area_size_top;
path_area = zeros([1 2]);

for k = 1:(n1/2)+1
    if (break_point(k+1)-break_point(k)) == selected_area
        path_area = pb2_vertices(break_point(k):break_point(k+1),:);    %path_area(m,n)=(y,x)
    end
end

%==================== boundary setting ====================

path_area_sorted = sortrows(path_area);
[path_area_sorted_m path_area_sorted_n] = size(path_area_sorted);
boundary_1 = zeros(1,2);
boundary_2 = zeros(1,2);
boundary_c1 = 1;
boundary_c2 = 1;

divided_point = uint8(1);
for l = 2:path_area_sorted_m
    if path_area_sorted(l,1)-path_area_sorted(l-1,1) > 60
       divided_point = uint8(l-1);
    end


end
boundary_1 = path_area_sorted(1:divided_point,:);
boundary_2 = path_area_sorted(divided_point+1:end-1,:);

% setting the p_boundary as a straight line if there is only a point in boundary
if size(boundary_1) == [1 2]
    p_boundary1 = [0 boundary_1(1,1)]
    
else
    p_boundary1 = polyfit(boundary_1(:,2),boundary_1(:,1),1);
end
if size(boundary_2) == [1 2]
    p_boundary2 = [0 boundary_2(1,1)];
    
else
    p_boundary2 = polyfit(boundary_2(:,2),boundary_2(:,1),1);
end

x_boundary = double(linspace(251,450));
f_boundary1 = double(polyval(p_boundary1,x_boundary));
f_boundary2 = double(polyval(p_boundary2,x_boundary));
target_path_boundary = (f_boundary1+ f_boundary2)/2;
target_path = zeros([100 2],'double');
target_path(:,1) = target_path_boundary+251;
target_path(:,2) = x_boundary;
p_path = polyfit(target_path(:,2),target_path(:,1),1);
p_path_1 = p_path(1);
p_path_2 = p_path(2);


% % ====================  publish the designed path ==================== 
r = rosrate(10);
pub = rospublisher('path','geometry_msgs/Point',"DataFormat","struct");
msg = rosmessage('geometry_msgs/Point',"DataFormat","struct");
msg.X = target_path(:,2);
msg.Y = target_path(:,1);
send(pub,msg);


end     

[Karthik Reddy Vennapureddy]

Hi JhenMin,

Are you able to directly run the above script without any issues in MATLAB, but facing issues only using MATLAB Coder when generating the code?

Thanks,

Karthik Reddy

[JhenMin Hung]

Yes, it runs well in MATLAB, but only facing the issue while generating the code. And it also faced the same error when i used the function

[ros_msg,status,statustext] = receive(segnet_img_sub);