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plot

Plot aligned estimated trajectory and error metrics

Since R2024b

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Syntax

plot(metrics,metricType)
ax = plot(___)
plot(___,Name=Value)

Description

plot(metrics,metricType) plots the aligned estimated trajectory and error values, color-coding the trajectory based on the specified metric type metricType, and the error values, linearly mapped to colors in the current colormap.

example

ax = plot(___) additionally returns the axes handle.

plot(___,Name=Value) specifies options using one or more name-value arguments in addition to the previous syntax. For example, ShowGroundTruth=false, suppresses the display of the ground truth trajectory.

Examples

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This example uses:

Open Live Script

Perform monocular visual simultaneous localization and mapping (vSLAM) using the data from the TUM RGB-D Benchmark. You can download the data to a temporary directory using a web browser or by running this code:

baseDownloadURL = "https://cvg.cit.tum.de/rgbd/dataset/freiburg3/rgbd_dataset_freiburg3_long_office_household.tgz"; 
dataFolder = fullfile(tempdir,"tum_rgbd_dataset",filesep); 
options = weboptions(Timeout=Inf);
tgzFileName = dataFolder+"fr3_office.tgz";
folderExists = exist(dataFolder,"dir");

% Create a folder in a temporary directory to save the downloaded file
if ~folderExists  
    mkdir(dataFolder) 
    disp("Downloading fr3_office.tgz (1.38 GB). This download can take a few minutes.") 
    websave(tgzFileName,baseDownloadURL,options); 
    
    % Extract contents of the downloaded file
    disp("Extracting fr3_office.tgz (1.38 GB) ...") 
    untar(tgzFileName,dataFolder); 
end

Create an imageDatastore object to store all the RGB images.

imageFolder = dataFolder+"rgbd_dataset_freiburg3_long_office_household/rgb/";
imds = imageDatastore(imageFolder);

Specify your camera intrinsic parameters, and use them to create a monocular visual SLAM object.

intrinsics = cameraIntrinsics([535.4 539.2],[320.1 247.6],[480 640]);
vslam = monovslam(intrinsics,TrackFeatureRange=[30,120]);

Process each image frame, and visualize the camera poses and 3-D map points. Note that the monovslam object runs several algorithm parts on separate threads, which can introduce a latency in processing of an image frame added by using the addFrame function.

for i = 1:numel(imds.Files)
    addFrame(vslam,readimage(imds,i))

    if hasNewKeyFrame(vslam)
        % Display 3-D map points and camera trajectory
        plot(vslam);
    end

    % Get current status of system
    status = checkStatus(vslam);
end

Figure contains an axes object. The axes object with xlabel X, ylabel Y contains 12 objects of type line, text, patch, scatter. This object represents Camera trajectory.

Plot intermediate results and wait until all images are processed.

while ~isDone(vslam)
    if hasNewKeyFrame(vslam)
        plot(vslam);
    end
end

Figure contains an axes object. The axes object with xlabel X, ylabel Y contains 12 objects of type line, text, patch, scatter. This object represents Camera trajectory.

After all the images are processed, you can collect the final 3-D map points and camera poses for further analysis.

xyzPoints = mapPoints(vslam);
[camPoses,addedFramesIdx] = poses(vslam);

% Reset the system
reset(vslam)

Compare the estimated camera trajectory with the ground truth to evaluate the accuracy.

% Load ground truth
gTruthData = load("orbslamGroundTruth.mat");
gTruth     = gTruthData.gTruth;

% Evaluate tracking accuracy
mtrics = compareTrajectories(camPoses, gTruth(addedFramesIdx), AlignmentType="similarity");
disp(['Absolute RMSE for key frame location (m): ', num2str(mtrics.AbsoluteRMSE(2))]);
Absolute RMSE for key frame location (m): 0.093645

% Plot the absolute translation error at each key frame
figure
ax = plot(mtrics, "absolute-translation");
view(ax, [2.70 -49.20]);

Figure contains an axes object. The axes object with title Absolute Translation Error, xlabel X, ylabel Y contains 2 objects of type patch, line. These objects represent Estimated Trajectory, Ground Truth Trajectory.

Input Arguments

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Trajectory Error metrics, specified as a trajectoryErrorMetrics object.

Metric type, specified as "absolute-rotation", "absolute-translation, "relative-rotation", or "relative-translation".

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: plot(metric,metricType,ShowGroundTruth=false), suppresses the display of the ground truth trajectory.

Point cloud vertical axis and direction, specified as "ZUp", "ZDown", "XUp", "XDown", "YUp", or "YDown". This argument sets the axis of the point cloud as the vertical axis, with the positive direction based on the value specified.

Display ground truth trajectory, specified as true or false.

Axes on which to display the visualization, specified as an Axes graphics object. To create an Axes object, use the axes function. To display the visualization in a new figure, leave Parent unspecified.

Output Arguments

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Axes handle, returned as an axes graphics object.

Version History

Introduced in R2024b

See Also

Objects