[eyetracker] new data, updated assignment, part of solution

projects/project_eyetracker/solution/convert_indices_to_time.m

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+function [time] = convert_indices_to_time(indices, framerate)
+% [time] = convert_indices_to_time(indices, frame_rate)
+%
+% Converts the vector of frame indices to time. The time vector will start
+% at zero.
+%
+% Arguments:
+%           indices: vecor, the frame indices
+%           framerate:, scalar, the framerate in Hz
+%
+% Returns:
+%           time: vector, the time vector
+
+indices = indices - indices(1);
+time = indices / framerate;

projects/project_eyetracker/solution/convert_pixel_to_meter.m

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+function [x, y] = convert_pixel_to_meter(x_pos, y_pos, width_m, height_m, width_pixel, height_pixel)
+
+x_resolution = width_m/width_pixel;
+y_resolution = height_m/height_pixel;
+
+x = x_pos * x_resolution;
+y = y_pos * y_resolution;

projects/project_eyetracker/solution/correct_eye_positions.m

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+function [true_x, true_y] = correct_eye_positions(eye_x, eye_y, x_offset, y_offset)
+% [true_x, true_y] = correct_eye_positions(eye_x, eye_y, x_offset, y_offset)
+% 
+% Applies the measured offset between x- and y- fixation coordinates to
+% correct the recorded x- and y- eye coordinates.
+%
+% Arguments:
+%           eye_x, eye_y: vector, the recorded x- and y-eye positions.
+%           x_offset, y_offset: scalar, the x- and y-offset between
+%           fixation point and eye position during fixation.
+%
+% Returns:
+%           true_x, true_y: vector, the corrected eye positions
+
+
+true_x = eye_x + x_offset;
+true_y = eye_y + y_offset;

projects/project_eyetracker/solution/fix_eye_lost.m

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+function [new_x, new_y] = fix_eye_lost(x, y, frame_index, eye_found)
+% [new_x, new_y] = fix_eye_lost(x, y, frame_index, eye_found)
+%
+% Fixes intervals in the data in which eye detection was lost. Function uses linear interpolation.
+%
+% Arguments:
+%           x, y: vector, the eye positions
+%           frame_indices: vector, same length as x and y, the frame
+%           indices (or times)
+%           eye_found: vector, ones and zeros indicate whether the eye was
+%           reliably found by the tracker or not.
+%
+% Returns:
+%           new_x, new_y: vectors of double, the new positions
+
+valid_x_positions = double(x(eye_found == 1));
+valid_y_positions = double(y(eye_found == 1)); 
+
+valid_frame_indices = double(frame_index(eye_found == 1));
+
+new_x = interp1(valid_frame_indices, valid_x_positions, double(frame_index));
+new_y = interp1(valid_frame_indices, valid_y_positions, double(frame_index));

projects/project_eyetracker/solution/get_fixation_offset.m

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+function [x_offset, y_offset] = get_fixation_offset(eye_x, eye_y, event_marker, fixation_event_marker, fixation_x, fixation_y)
+% [x_offset, y_offset] = get_fixation_offset(eye_x_pos, eye_y_pos, event_marker, fixation_event_marker, fixation_x, fixation_y)
+% 
+% Estimates the x, and y-offset between screen position and reported eye position while fixating
+%
+% Arguments: 
+%            eye_x, eye_y: The eye positions reported by the tracker, vectors of coordinates
+%            event_marker: vector, the recorded event markers 
+%            fixation_event_marker: scalar, the event marker that represents the fixation period
+%            fixation_x, fixation_y: scalar, the x and y position of the fixation cross on the screen
+%            
+% Returns:
+%            x_offset, y_offset: scalar the deviation between reported x
+%            and y positions and the true positions.
+
+eye_fixation_x_pos = median(eye_x(event_marker == fixation_event_marker));
+eye_fixation_y_pos = median(eye_y(event_marker == fixation_event_marker));
+
+x_offset = fixation_x - eye_fixation_x_pos;
+y_offset = fixation_y - eye_fixation_y_pos;

projects/project_eyetracker/solution/load_eye_tracking_data.m

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+function [frame_index, gaze_x, gaze_y, marker, eye_found] = load_eye_tracking_data(filename)
+% [frame_index, gaze_x, gaze_y, marker, eye_found] = load_eye_tracking_data(filename)
+%
+% Loads the eyetracking data stored in the specified file. Raises an error,
+% if the file was not found.
+% 
+% Arguments:
+%           filename: string, the path to the data file
+%
+% Returns:
+%           frame_index: vector, the recorded frame numbers
+%           gaze_x, gaze_y: vector, the recorded x and y eye positions
+%           marker: vector, the recorded event marker
+%           eye_found: vector, 1, or zero values indicating whether or not
+%           the eye was actually detected by the tracker.
+
+if exist(filename, "file") ~= 2 
+   error("file %s does not exist or is no mat file", filename);
+end
+
+load(filename, "gaze_x", "gaze_y", "frame_index", "marker", "eye_found")

projects/project_eyetracker/solution/main.m

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+% Project Eyetracking
+% Name: John Doe
+% Matrikelnummer: 123456789
+clear
+close all 
+
+%% Definition of constants
+framerate = 60;  % Hz
+screen_width = 0.376;  % m
+screen_height = 0.301;  % m
+screen_resolution_x = 1280;  % pixel
+screen_resolution_y = 1024;  % pixel
+fixation_x = screen_resolution_x/2;  % position of fixation cross on screen
+fixation_y = screen_resolution_y/2;  % position of fixation cross on screen
+fixation_marker = 1;  % event marker for fixtion period
+movement_marker = 2;  % event marker for free movement period
+
+data_files = [fullfile("..", "data", "1_1.mat"), fullfile("..", "data", "1_5.mat")];
+scenes = [fullfile("..", "data", "Genesis_VIII.png"), fullfile("..", "data", "Genesis_XXXIX.png")];
+
+%% Process files
+for i = 1:length(data_files)
+    file = data_files(i);
+    scene = scenes(i);
+    
+    fprintf("processing: %s\n", file)
+    [frame_indices, x, y, event_marker, eye_found] = load_eye_tracking_data(file);
+    [x_offset, y_offset] = get_fixation_offset(x, y, event_marker, fixation_marker, fixation_x, fixation_y);
+    [true_x, true_y] = correct_eye_positions(x, y, x_offset, y_offset); 
+    [true_x, true_y] = fix_eye_lost(true_x, true_y, frame_indices, eye_found);
+    time = convert_indices_to_time(frame_indices, framerate);
+    
+    fig = plot_image_position_overlay(true_x, true_y, time, scene);
+    saveas(fig, sprintf("test_%i", i), "pdf")
+end

projects/project_eyetracker/solution/plot_image_position_overlay.m

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+function fig = plot_image_position_overlay(x, y, time, image)
+
+if length(x) ~= length(y) || length(y) ~= length(time)
+    error("Length of vectors x, y, and time does not match!");
+end
+if ~exist(image, "file")
+    error("Image %s could not be found!", image);
+end
+
+fig = figure();
+imshow(image)
+hold on
+scatter(x, y, [], time)
+c = colorbar();
+
+fig.PaperSize = [10.0, 10.0];
+fig.PaperPosition = [0., 0., 10.0, 10.0];
+c.Label.String = "time [s]";
+c.Label.FontSize = 9;
+