Hello Jibril,
As per my understanding, you want to visualize and compare the algorithm results with the ground truth data. And, the ground truth data is available in the "groundtruth.txt" file.
MATLAB provides a function called "importdata()", that loads a data array from a file. The Monocular SLAM example, makes use of ".mat" file to load the ground truth data. You can also convert the ".txt" to ".mat" file. An example code for the same would look like:
% Loading data from .txt file
gTruthData = importdata("groundtruth.txt");
% Save data to .mat file
save('groundtruth.mat','gTruthData');
% Load data from .mat file
gTruthData = load("groundtruth.mat");
You can refer to the following documentation on "importdata" for more information:
