MATLAB coder error while using 'rospublisher'

Question

JhenMin Hung 2023-7-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2000672-matlab-coder-error-while-using-rospublisher

评论： JhenMin Hung 2023-8-1

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.

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Answer 1

Karthik Reddy Vennapureddy 2023-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/2000672-matlab-coder-error-while-using-rospublisher#answer_1280927

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

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JhenMin Hung 2023-7-31

在 MATLAB Online 中打开

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     