The function "estimateW​orldCamera​Pose"retur​ns null values for rotation matrix and the translateur vector

Good morning,

I need to use the function "estimateWorldCameraPose" to calculate the rotation matrix and the translation vector.

I am using a picture where the object is a circle.

With a function I designed based on a tutorial, I got the coordinates in 2D of the center of the circle.

I also have the 3D coordinates of the center measured by other software.

My problem is that I have Null values for the rotation matrix and the translation vector and I cannot figure out.

Can you help me please?

Thanks for your help.

The picture used is that one:

The function I used is that one:

function [markers, diameter] = Find_the_center_circle(fullImages)
%% Definition of plotting variables
captionFontSize = 14;

%% Convertion to gray scale 
GrayImage = rgb2gray(fullImages);

%% Identification of each blob which are constituted the picture
% Identify individual blobs by seeing which pixels are connected to each other.
% Each group of connected pixels will be given a label, a number, to identify it and distinguish it from the other blobs.
% Do connected components labeling with either bwlabel() or bwconncomp().
% Label each blob so we can make measurements of it.
labeledImage = bwlabel(GrayImage, 8);     

% Get all the blob properties.  Can only pass in originalImage in version R2008a and later.
blobMeasurements = regionprops(labeledImage, GrayImage, 'all');
numberOfBlobs = size(blobMeasurements, 1);

%% Plot the the circle's imprint
imshow(GrayImage);
title('Outlines, from bwboundaries()', 'FontSize', captionFontSize); 
% Make sure image is not artificially stretched because of screen's aspect ratio.
axis image; 
hold on;

boundaries = bwboundaries(GrayImage);
numberOfBoundaries = size(boundaries, 1);
for k = 1 : numberOfBoundaries
	thisBoundary = boundaries{k};
	plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 2);
end
hold off;

%% Deterination of the centre abd tge size of each circle
% We can get the centroids of ALL the blobs into 2 arrays,
% one for the centroid x values and one for the centroid y values.
allBlobCentroids = [blobMeasurements.Centroid];
centroidsX = allBlobCentroids(1:2:end-1);
centroidsY = allBlobCentroids(2:2:end);

hold on;
% Loop through all blobs.
for k = 1 : numberOfBlobs           
    plot(centroidsX(k), centroidsY(k), 'bx', 'MarkerSize', 10, 'LineWidth', 2);
end

%% Outputs of the function
markers  = [centroidsX, centroidsY];
diameter = blobMeasurements.Perimeter;
end

The following code is what I used:

%Definition of loop counters
% Ncams    = length(imRects);
nCams    = 1;
Npicture = 1;

%Definition parameters for estimateWorldCameraPose
confidence      = 99.9;      %Confidence parameter for 'Confidence'
max_error_repro = 1.5;       %Reprojecction error for 'MaxReprojectionError'

%Focal length in meters (given by the datasheet of the camera)
Focal_length = 3.04e-3;

%Blender resolution
res_x = 1920;
res_y = 1800;


markerLocations = 1.0e+03 *[0.13689/(pi*2), 2.2718/(pi*2), 0.011503];


%Definition structures
gantryCalib.R            = cell(1, nCams);
gantryCalib.T            = cell(1, nCams);
markerCamLocalisation    = cell(1, nCams);
goodMeasure              = cell(1, nCams);
triPositions             = cell(1, nCams);
camCsTot                 = cell(1, nCams);
usedPicture              = cell(1, nCams);

%Definition tables
Rs                       = zeros(3, 3, Npicture);
Ts                       = zeros(Npicture, 3);
markerLocationsCalculate = zeros(length(markerLocations), 2, Npicture);
measure                  = false(Npicture, 1);
goodPicture              = zeros(Npicture, 1);
camCs(1: Npicture)       = CoOrdinateSystem_R_T;

%% Generation intrinsic parameters
%Determination of the size of the picture
fPicture  = ['Cam', int2str(1), '_', sprintf('%0.4d', 1)];
imSize    = size(CropImage);

%Calculation of the intrinsic matrix K = [f_x, s, o_x; 0, f_y, o_y; 0, 0, 1]
piCam.F = Focal_length;                  % focal length in meters
piCam.r = [res_x, res_y];                % origional resolution
piCam.p = 1.4e-6 * piCam.r(1)/imSize(1); % pixel size in meters, scaled for the cropped image resolution
piCam.s = 1 /piCam.p;                    % pixels per metre
piCam.f = piCam.F * piCam.s;             % focal length in pixels
piCam.c = imSize([2,1])/2;               % principal point in pixels
piCam.I = [piCam.f, 0,0; 0 piCam.f,0;piCam.c,1];

piCam.camParam  = cameraParameters('IntrinsicMatrix', piCam.I);

%% Calibration
for i = 1:nCams
    camName   = ['Camera', int2str(i),'_*.png'];
    FlistFull = dir(fullfile(FullFolder, camName));
    FlistFull.name;
    
    for j = 1:Npicture
        %Load picture
        FullImage = imread(fullfile(FullFolder, FlistFull(j).name));
        
        %Detection markers
        if(100 < length(CropImage))

            [markers, diameter] = Find_the_center_circle(FullImage);
           
%           %Verification place of the markers
            f = figure;
            imshow(FullImage);
            hold on;
            plotDots(markers1, 200, 'b', '.');
            hold off;
%             
        else
            markers = 0;
            fprintf('Error in image %d, camera %d, incorrect number of markets \n', j, i);
        end
        
        [s, add] = size(markers);
        
        if(s == 1)
            %Calibration
            [r, t, inliers, status] = estimateWorldCameraPose(markers, markerLocations, piCam.camParam, ...
                                                'Confidence', confidence, ...
                                                'MaxReprojectionError', max_error_repro);
            
            
        end
    end
end

[Matt J]

You would need to provide code and image attachments so that we can reproduce the results ourselves.

[Claire Pottier]

Ok, I will modify my request

[Matt J]

No, this doesn't run

Undefined function or variable 'CoOrdinateSystem_R_T'.
Error in test (line 38)
camCs(1: Npicture)       = CoOrdinateSystem_R_T; 

If the problem is in this line,

            [r, t, inliers, status] = estimateWorldCameraPose(markers, markerLocations, piCam.camParam, ...
                                                'Confidence', confidence, ...
                                                'MaxReprojectionError', max_error_repro);

then just attach a .mat file with the inputs needed to run that line.

[Claire Pottier]

Hi Matt,

I forgot to give you one function, all my apologies.

Unfortunately, you need to have the whole script to run it.

Here is the script of the missing function:

classdef CoOrdinateSystem_R_T
% The CoOrdinateSystem class is used to store the Origin and xyz unit
% vectors for a co-ordinate system.
%
% obj = CoOrdinateSystem()
%   create default co-ordinate system
%
% obj = CoOrdinateSystem(C)
%   create unrotated cs with origin at C
%
% obj = CoOrdinateSystem(C,R)
%   create rotated cs with unit vectors as the columns of R and
%   centered at C    
%
% Methods
%  R = getRotationMatrix(obj)
%    get the columwise rotation matrix from the cs object
    properties
        O = [0 0 0];     % [ Origin ]
        i = [1 0 0];     % [ x axis vector ]
        j = [0 1 0];     % [ y axis vector ]
        k = [0 0 1];     % [ Z axis vector ]
    end
    
    methods
        function obj = CoOrdinateSystem_R_T(varargin)
            % obj = CoOrdinateSystem()
            %   create default co-ordinate system
            %
            % obj = CoOrdinateSystem(C)
            %   create unrotated cs with origin at C
            %
            % obj = CoOrdinateSystem(C,R)
            %   create rotated cs with unit vectors as the columns of R and
            %   centered at C
            
            switch nargin                                    
                case 1
                    obj.O = varargin{1};
                case 2
                    obj.O = varargin{1};
                    obj.i = varargin{2}(:,1)';
                    obj.j = varargin{2}(:,2)';
                    obj.k = varargin{2}(:,3)';
            end
            
        end
        
        function R = getRotationMatrix(obj)
            R = [obj.i' , obj.j', obj.k'];
        end
    end
    
end

[Claire Pottier]

Hey everybody

Sorry for my persistence, but do you know where the problem is in my script?

Thank you for your answers