This is the primary repository for the third project in the Udacity Robotics Nanodegree. The goal of the project is to identify and collect objects in a crowded space using the PR2.
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README.md

Udacity - Robotics NanoDegree Program

Project 3: 3D Perception in a Cluttered Space

Udacity Robotics Nanodegree
October 2017

Overview

The goal of this project is to program a PR2 to identify and acquire target objects from a cluttered space and place them in a bin. The project is based on the 'Stow Task' portion of Amazon's Robotics Challenge.

(Click the image for a video of the final result) Click for the final project video

Specifically, the objectives of this project are to:

1. Have the PR2 image its world

2. Identify objects from the pick list

3. Maneuver the PR2 towards the objects

4. Grasp the object

5. Maneuver the PR2 towards the object's destination bin

6. Sucessfully place the object in the bin

If you'd like to watch the PR2 in action, click here.

Check out the Amazon Robotics Challenge here.

For those interested, here is a great video on a highly accurate grasping robot. And the dataset that powers it is now free and open to the public!

We operate PR2 through ROS Kinetic (ran through Linux Ubuntu 16.0) and commands are written in Python.

The code driving this project and interacting with ROS can be found at project_template.py

Quick note on naming convention: THIS_IS_A_CONSTANT and thisIsAVariable

This README is broken into the following sections: Environment Setup, Code Analysis, and Debugging.

Environment Setup

If you don't already have the directory made:

$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/
$ catkin_make

Then, clone the project repo:

$ cd ~/catkin_ws/src
$ git clone https://github.com/udacity/RoboND-Perception-Project.git

Install missing dependencies:

$ cd ~/catkin_ws
$ rosdep install --from-paths src --ignore-src --rosdistro=kinetic -y

Build it:

$ cd ~/catkin_ws
$ catkin_make

Add the following to your .bashrc file:

export GAZEBO_MODEL_PATH=~/catkin_ws/src/RoboND-Perception-Project/pr2_robot/models:$GAZEBO_MODEL_PATH

And if it's not there already, also add this to .bashrc:

source ~/catkin_ws/devel/setup.bash

Filtering and Segmentation Exercises Using the python-pcl library, which can be invoked using import pcl

Point Cloud Library

We'll be running the code through our linux distribution of ROS.

Robotic VM V2.0.1 is the directory that contains the Linux Boot image:Ubuntu 64-bit Robo V2.0.1.ova

If prompted, the Linux system password is robo-nd

Code Analysis

OpenCV

Quick note on openCV: although we won't be using OpenCV to calibrate our camera(we'll be using a ROS package), the process for doing so with OpenCV is outlined here:

1. Use cv2.findChessboardCorners() to find corners in chessboard images and aggregate arrays of image points (2D image plane points) and object points (3D world points) . 2. Use the OpenCV function cv2.calibrateCamera() to compute the calibration matrices and distortion coefficients. 3. Use cv2.undistort() to undistort a test image.

OpenCV functions for calibrating camera: findChessboardCorners() and drawChessboardCorners()

Filtering

First, we're going to walk through some filtering techniques that will help give us only the parts of the point cloud we're intrested in.

We'll harness some filters from the Point Cloud Library

VoxelGrid Downsampling Filter

alt text

Downsampling is used to decrease the density of the pointcloud that is output from the RGB-D camera. This is done because the very feature rich pointclouds can be quite computationally expensive. Downsampling can be thought of decreasing the resolution of a three dimensional point cloud.

RANSAC.py contains the Voxel Downsampling Code.

Pass Through Filtering

We'll use Pass Through Filtering to trim down our point cloud space along specified axes, in order to decrease the sample size. We will allow a specific region to Pass Through. This is called the Region of Interest. Pass Through Filtering can be thought of as cropping a three dimensional space across one or many of the dimensions.

RANSAC Plane Fitting

We can model the table in our dataset as a plane, and remove it from the pointcloud using Random Sample Consensus or RANSAC algorithm.

As you can see, we selected the horizontal plane below, which was the table our target objects were sitting on.

alt text

Extracting Indices - Inliers and Outliers

Once we've determined where our table is located, we can create two separate point clouds: one for the table(inliers), and one for the objects beyond(outliers).

Inliers extracted_inliers = cloud_filtered.extract(inliers, negative=False)

Outliers extracted_outliers = cloud_filtered.extract(inliers, negative=True)

Outlier Removal Filter

alt text

This filter is used to statistically remove noise from the image. Here's a cool video showing the removal in 3 dimensions.

Much like the previous filters, we start by creating a filter object:

outlier_filter = cloud_filtered.make_statistical_outlier_filter()

Set the number of neighboring points to analyze for any given point:

outlier_filter.set_mean_k(50)

Set threshold scale factor:

x = 1.0

Any point with a mean distance larger than global (mean distance+x*std_dev) will be considered an outlier

outlier_filter.set_std_dev_mul_thresh(x)

Finally call the filter function

cloud_filtered = outlier_filter.filter()

Clustering for Segmentation

Now that we've used shape attributes in the dataset to filter and segment the data, we'll move on to using other elements of our dataset such as: color and spatial properties

K-Means Clustering

K-Means Clustering is an appropriate clustering algorithm if you are aware of your dataspace and have a rough idea of the number of clusters.

Remember, with K-Means, we:

1. Choose the number of k-means (the number of clusters to look for) 2. Define the convergence / termination criteria (stability of solution / number of iterations) 3. Select the initial centroid locations, or randomly generate them 4. Calculate the distance of each datapoint to each of the centroids 5. Assign each of the datapoints to one of the centroids(clusters) based upon closest proximity 6. Recompute the centroid based on the datapoints that belong to it 7. Loop back to Step 4 until convergence / termination criteria is met

alt text

If you are unsure of the number of clusters, it is best to use a different clustering solution! Such as DBSCAN...

DBSCAN Algorithm (Density-Based Spatial Clustering of Applications with Noise)

Sometimes called Euclidean Clustering

DBSCAN is a nice alternative to k-means when you don't know how many clusters to expect in your data, but you do know something about how the points should be clustered in terms of density (distance between points in a cluster).

alt text

Original data on the left and clusters identified by the DBSCAN algorithm on the right. For DBSCAN clusters, large colored points represent core cluster members, small colored points represent cluster edge members, and small black points represent outliers.

DBSCAN datapoints do not have to be spatial data; they can be color data, intensity values, or other numerical features! This means we can cluster not only based upon proximity, but we can cluster similarly colored objects!

Run the VM to test our filtering and segmentation code

Downsampling, Passthrough, RANSAC plane fitting, extract inliers/outliers

$ roslaunch sensor_stick robot_spawn.launch

segmentation.py contains all of our filtering code. Run it with:

$ ./segmentation.py

When you click on topics in RViz, you should be able to only see this view when the pcl_objects topic is selected:

alt text

Object Recognition

HSV

HSV can help us identify objects when the lighting conditions change on an RGB image. Hue is the color, Saturation is the color intensity, and Value is the brightness. A conversion from RGB to HSV can be done with OpenCV:

hsv_image = cv2.cvtColor(rgb_image, cv2.COLOR_RGB2HSV)

Color Histograms

Using color historgrams, we can identify the color pattern of an object, and not be limited to spatial data. Let's use this example of the Udacity can:

alt text

Using numpy, we can create a histogram for each one of the color channels. See color_histogram.py to see how we do this with code. The result is:

alt text

This is the RGB Signature of the blue Udacity can!

Surface Normals

Just as we did with plotting colors, we'll now want to plot shape. This can be done by looking at the surface normals of a shape in aggregate. We'll also analyze them using histograms like the ones below:

alt text

These surface normal histograms correspond to the following shapes: alt text

B represents the cube, A represents the sphere, and C represents the pyramid

Support Vector Machines (SVM)

"SVM" is just a funny name for a particular supervised machine learning algorithm that allows you to characterize the parameter space of your dataset into discrete classes. It is a classification technique that uses hyperplanes to delineate between discrete classes. The ideal hyperplane for each decision boundary is one that maximizes the margin, or space, from points.

alt text

Scikit-Learn or sklearn.svm.SVC will help us implement the SVM algorithm. Check this link out for documentation on scikit-learn

svm.py will house our SVM code and generate_clusters.py will help us create a random dataset.

svc = svm.SVC(kernel='linear').fit(X, y)

The line above is the one doing the heavy lifting. The type of delineation can be changed. It must be one of ‘linear’, ‘poly’, ‘rbf’, ‘sigmoid’, ‘precomputed’ or a callable. Read more here.

We also do some SVM Image Classification, and this can be found under svm_image_classifer.

Recognition Exercise - Combining what we have learned!

This is a very good confusion matrix. Initially, ours will not come out this good. alt text

$ cd ~/catkin_ws
$ roslaunch sensor_stick training.launch

Once the environment is up, then:

$ cd ~/catkin_ws
$ rosrun sensor_stick capture_features.py

The capture_features.py script should randomly place the 7 objects infront of the RGB-D camera and capture features about the items, then output training_set.sav

Then, to generate the confusion matrix:

$ rosrun sensor_stick train_svm.py

As you can see, this is not a good confusion matrix. That's because the functions compute_color_histograms() and compute_normal_histograms(), in the file features.py is not appropriately filled out.

You can find features.py in the directory:

~/catkin_ws/src/sensor_stick/src/sensor_stick/

First up, we'll alter the compute_color_histograms() function, which will do RGB color analysis on each point of the point cloud.

def compute_color_histograms(cloud, using_hsv=False):

    # Compute histograms for the clusters
    point_colors_list = []

    # Step through each point in the point cloud
    for point in pc2.read_points(cloud, skip_nans=True):
        rgb_list = float_to_rgb(point[3])
        if using_hsv:
            point_colors_list.append(rgb_to_hsv(rgb_list) * 255)
        else:
            point_colors_list.append(rgb_list)

    # Populate lists with color values
    channel_1_vals = []
    channel_2_vals = []
    channel_3_vals = []

    for color in point_colors_list:
        channel_1_vals.append(color[0])
        channel_2_vals.append(color[1])
        channel_3_vals.append(color[2])

    nbins=32
    bins_range=(0,256)
    
    # Compute histograms
    r_hist = np.histogram(channel_1_vals, bins=nbins, range=bins_range)
    g_hist = np.histogram(channel_2_vals, bins=nbins, range=bins_range)
    b_hist = np.histogram(channel_3_vals, bins=nbins, range=bins_range)
    
    # Extract the features
    # Concatenate and normalize the histograms
    hist_features = np.concatenate((r_hist[0], g_hist[0], b_hist[0])).astype(np.float64)
    normed_features = hist_features / np.sum(hist_features)  

    return normed_features 

Next, we'll add the histogram, compute features, concatenate them, and normalize them for the surface normals function compute_normal_histograms. Remember to aleter the range of the histograms here,as compared to the RGB histograms above. 0-255 was our range there, but here it will be from -1 to 1:

def compute_normal_histograms(normal_cloud):
    norm_x_vals = []
    norm_y_vals = []
    norm_z_vals = []

    for norm_component in pc2.read_points(normal_cloud,
                                          field_names = ('normal_x', 'normal_y', 'normal_z'),
                                          skip_nans=True):
        norm_x_vals.append(norm_component[0])
        norm_y_vals.append(norm_component[1])
        norm_z_vals.append(norm_component[2])


    nbins=32
    bins_range=(-1,1)
    # Compute histograms of normal values (just like with color)

    # Compute histograms
    x_hist = np.histogram(norm_x_vals, bins=nbins, range=bins_range)
    y_hist = np.histogram(norm_y_vals, bins=nbins, range=bins_range)
    z_hist = np.histogram(norm_z_vals, bins=nbins, range=bins_range)
    
    # Concatenate and normalize the histograms
    hist_features = np.concatenate((x_hist[0], y_hist[0], z_hist[0])).astype(np.float64)
    normed_features = hist_features / np.sum(hist_features)  

    return normed_features

Now, we can relaunch the Gazebo environment, re-run the training and feature capture, then generate the confusion matrix:

$ cd ~/catkin_ws
$ roslaunch sensor_stick training.launch

Once the environment is up, then:

$ cd ~/catkin_ws
$ rosrun sensor_stick capture_features.py

Give it a minute or so to go through all 7 objects. Then:

$ rosrun sensor_stick train_svm.py

The outputted confusion matrix should be better than the previous one. But there are still strategies to improve:

  • Convert RGB to HSV
  • Compute features for a larger set of random orientations of the objects
  • Try different binning schemes with the histogram(32,64, etc)
  • Modify the SVM parameters(kernel, regularization, etc)

To modify how many times each object is spawned randomly, look for the for loop in capture_features.py that begins with for i in range(5): Increase this loop to increase the number of times you capture random orientations for each object.

To use HSV, find the line in capture_features.py where you're calling compute_color_histograms() and change the flag to using_hsv=True.

To mess with the SVM parameters, open up train_svm.py and find where you're defining your classifier. Check out the sklearn.svm docs to see what your options are there.

After setting using_hsv=true and bins=32(which seems to be a sweet spot), I began playing with the other two features, number of random orientations, and SVM kernel, in order to improve the accuracy of my object classifier. Note, I didn't use poly, as it gave very low accuracy (17%).

My results were as follows, with using_hsv=true and bins=32:

  • 64% with SVM kernel=linear, orientations=7
  • 64% with SVM kernel=rbf, orientations=10
  • 74% with SVM kernel=linear, orientations=10
  • 79% with SVM kernel=linear, orientations=20
  • 82% with SVM kernel=sigmoid, orientations=20
  • 84% with SVM kernel=rbf, orientations=20

It seems as though our accuracy is improving with orientations increasing--which makes logical sense as we increase the sample size of the training set, our algorithm gets better. Let's continue increasing orientations exposed to the camera, to 40:

  • 88% with SVM kernel=sigmoid, orientations=40
  • 89% with SVM kernel=linear, orientations=40
  • 90% with SVM kernel=rbf, orientations=40

And at 80 orientations per object:

  • 89% with SVM kernel=sigmoid, orientations=80
  • 90% with SVM kernel=rbf, orientations=80
  • 95% with SVM kernel=linear, orientations=80

Make sure you are in the directory where model.sav is located!

$ roslaunch sensor_stick robot_spawn.launch
$ ./object_recognition.py

Putting it all together for our Project's Perception Pipeline

In the previous exercises, we have built out much of our perception pipeline. Building on top of object_recognition.py we'll just have to add a new publisher for the RGB-D camera data, add noise filtering, and a few other items. Let's get started!

Filter and Segment the New Scene

Since we have a new table environment, not all of our filters will be effective. I'm going to create a new file to replace segmentation.py that will help us filter and segment the new environment--I'll call it pr2_segmentation.py. Most of the code from segmentaion.py can just be copied over, but note the differences in the table height. This means we'll have to adjust the pass through filtering Z-axis minimum and maximum values.

For axis-min I'll try 0.6(meters) and 1.1(meters) for axis-max.

We'll also want to publish our RGB-D camera data to a ROS-topic named /pr2/world/points. Following the syntax of other publishers/subscribers should help us out with this.

Also, we'll have to deal with actual noise in this scene, so we'll apply what we learned earlier on and add in the statistical outlier remover to pr2_segmentation.py with:

outlier_filter = cloud_filtered.make_statistical_outlier_filter()
outlier_filter.set_mean_k(50)
x = 1.0
outlier_filter.set_std_dev_mul_thresh(x)
cloud_filtered = outlier_filter.filter()

This should leave pr2_segmentation.py just about ready to go, but to verify, we have the following items in the pcl_callback(pcl_msg) function:

  • Convert ROS message to PCL (goes from PC2 data to PCL pointXYZRGB)
  • Voxel Grid Downsampling (essentially reduce the resolution of our Point Cloud)
  • Statistical Outlier Removal Filter (gets rid of points that aren't apart of a group, determined by proximity)
  • Pass Through Filtering (a vertical cropping along the Z-axis that cuts down our Point Cloud)
  • RANSAC Plane Segmentation (helps find a plane - in this case the table)
  • Extract Inliers and Outliers (Create two point clouds from the RANSAC analysis)
  • Euclidean Clustering/DBSCAN (Calculates the distance to other points, and based on thresholds of proximity, combines groups of points into clusters that we assume are objects)
  • Cluster Mask (color each object differently so they are easily distinguished from one another)

We'll then want to make sure this new point cloud is published with:

pcl_cluster_pub = rospy.Publisher("/pcl_world", PointCloud2, queue_size=1)

To test everything out, open a new terminal in the ROS system, and type:

$ cd ~/catkin_ws/
$ roslaunch pr2_robot pick_place_project.launch

Give the PR2 a moment to visualize and map its surroundings. Once it's finished, type:

$ cd ~/catkin_ws/src/RoboND-Perception-Project/pr2_robot/scripts/
$ ./pr2_segmentation.py

You should now be able to go into RViz and click on the new ROS topics:pcl_world which is our filtered, segmented, and colored group of objects; and pr2/world/points which is the data coming from our PR2's RGB-D camera.

With this done, and once you are happy with the results, you can transfer the code. You'll find project_template.py in the /pr2_robot/scripts directory. This will be our new location for our primary project code. Port in the code from pr2_segmentation.py andobject_recognition.py into the respective TO DOs.

Capture Features of the New Objects

Just like we did in the lecture exercise, we need to capture the features of the objects that we will need to find in the project (essentially photograph them with the RGB-D camera from many different angles).

There will be 3 different "worlds". These can be found in the config directory of pr2_robot, and are named pick_list_1.yaml, pick_list_2.yaml, and pick_list_3.yaml.

Pick out the models from there (should be 8 models)and put their names into the models dictionary of capture_features.py. Then, set the number of random orientations each model will be exposed to in the for loop. I used 80 for higher accuracy. Lastly, change the very last line of the script to make sure my new feature set is not confused with previous ones. Set it to: training_set_worlds123.sav

We're now ready to capture our objects' features. Launch our handy sensor_stick Gazebo environment with:

$ roslaunch sensor_stick training.launch

Now, change the directory to where you want the feature set training_set_worlds123.sav to save. I put mine here:

$ cd ~/catkin_ws/src/RoboND-Perception-Project/pr2_robot/scripts/

Then, run the feature capture script:

$ rosrun sensor_stick capture_features.py

This will take some time. Mine took ~20 minutes running on a VM.

Once finished, you will have your features saved in that directory. We'll be using them in the next step when we train our classifier!

Train the SVM Classifier

We're now going to train our classifier on the features we've extracted from our objects. train_svm.py is going to do this for us, and is located where your directory should still be pointing:

$ cd ~/catkin_ws/src/RoboND-Perception-Project/pr2_robot/scripts/

Open train_svm.py and make sure line ~39 or so is loading the correct feature data we just produced:

training_set = pickle.load(open('training_set_worlds123.sav', 'rb'))

Then, we're going to check our SVC kernel is set to linear:

clf = svm.SVC(kernel='linear')

rbf and sigmoid also work well, but with 80 iterations, I've found linear to have the highest accuracy (93%).

Now, from this same directory, run the script:

$ rosrunh sensor_stick train_svm.py

Two confusion matrices will be generated--one will be a normalized version. Prior to any training, I had a very confused confusion matrix that looked like this:

If you did the above steps correctly, it should look closer to this:

This is a better looking confusion matrix

Check the Labeling in RViz

Now, we can check the labeling of objects in RViz. Exit out of any existing Gazebo or RViz sessions, and type in a terminal:

$ roslaunch pr2_robot pick_place_project.launch

Give it a moment to boot up, then change to our favorite directory, and run our project_template.py code:

$ cd ~/catkin_ws/src/RoboND-Perception-Project/pr2_robot/scripts/
$ rosrun pr2_robot project_template.py

It's important to run project_template.py from this directory because that is where model.sav lives; which is the output of our training of the Support Vector Machine classifier.

You've now completed your perception pipeline!

Output yaml Files

We now need to load each of the three worlds, and determine which objects to look for once we're there. The launch file pick_place_project.launch in pr2_robot/launch at lines 13 and 39 have world parameters you need to alter.

We now need to obtain our picklists from .yaml files that are located here: /pr2_robot/config/ They are called: pick_list_1.yaml, pick_list_2.yaml, and pick_list_3.yaml.

For instance, pick_list_1.yaml looks like this:

object_list:
  - name: biscuits
    group: green
  - name: soap
    group: green
  - name: soap2
    group: red

We want to read from our pick_list_X.yaml files, but then write back to output .yaml files that capture the objects we've encountered and where they're located.

Running the Project

For ease of use, I've built two separate shell scripts that run the above lines: launch.sh starts up Gazebo, and run.sh runs our project_template.py script. They can be invoked from the terminal with:

$ ./launch

Give the PR2 a moment... And open a new terminal window, and type:

$ ./run.sh

You'll be prompted in one of the terminal windows to click continue or next in RViz.

World 1

World 2

World 3

Debugging

Improving Real-time Factor in Gazebo

In the directory pr2_robot/worlds/, you'll find the test#.world files. Search for "physics", and find the block of code below:

    <physics name='default_physics' default='0' type='ode'>
      <max_step_size>0.005</max_step_size>
      <real_time_factor>1</real_time_factor>
      <real_time_update_rate>1000</real_time_update_rate>
    </physics>

This controls the rate of the Gazebo world, and since I was experiencing run-time rates of about 0.2, I needed to increase it by a factor of 5 to get to 1.0; so I set the max_step_size to 0.005 from 0.001. The product of max_step_size and real_time_update_rate gives you the expected real time factor.

Improving Accuracy

After some issues with object labeling and recognition, I decided to re-train on the 8 objects, but this time for 200 iterations each

Improving Grasping

Due to us running a Virtual instance of Linux Ubuntu, our PR2 doesn't always successfully grasp items. Let's put in a delay like we did in project2.

/pr2_robot/src/ has a c++ file named pr2_pick_place_server.cpp. Line 222 sets the delay of the right gripper and line 311 sets the delay after closing the left gripper. At default, these are set to 3.0 seconds, but let's bump that up to 8.0.

Because we changed one of the build files, we have to re-make the project. Close all terminal windows, open a new one, and type:

$ cd ~/catkin_ws/`
$ catkin_make

Improving Classification

Our classifier wasn't initially recognizing the books! We'll change a few features in filtering and clustering to make it perform better.

Voxel DownSampling

LEAF_SIZE = 0.003

Euclidean Clustering

    ec.set_ClusterTolerance(0.01)
    ec.set_MinClusterSize(200)
    # Refering to the minimum and maximum number of points that make up an object's cluster
    ec.set_MaxClusterSize(50000)

Logic for when Object Recognition has Completed Successfully We'll write some quick logic for when we've done a good enough job to start moving the PR2:

    object_list_param = rospy.get_param('/object_list')
    pick_list_objects = []
    for i in range(len(object_list_param)):
        pick_list_objects.append(object_list_param[i]['name'])
        
    print "\nPick List includes: "
    print pick_list_objects
    print "\n"
    pick_set_objects = set(pick_list_objects)
    detected_set_objects = set(detected_objects_labels)

    if detected_set_objects <= pick_set_objects:
        try:
            pr2_mover(detected_objects)
        except rospy.ROSInterruptException:
            pass
Improving Re-Classification

After much experience in the simulated robot world, I found that objects would get knocked around when the robot would plan an overly complex motion path. Therefore, objects would not be located at the initial centroids that were calculated. Although computationally more expensive, I decided to relocate the centroid for loop to be inside of the primary loop:

for i in range(0, len(object_list_param)):
    for object in object_list:
        labels.append(object.label)
        points_arr = ros_to_pcl(object.cloud).to_array()
        temp = np.mean(points_arr, axis=0)[:3]
        centroids.append(temp)
Improving Drop Location

Often, the biscuits object will get hung up on the front edge of the green box. We can solve this by changing the centroids of the boxes. These are located in /pr2_robot/config/dropbox.yaml

Open up this yaml file, and find the the x values. Since these are both 0 at default, we can assume this is the axis we need to alter. Let's change both boxes x-values to -0.1 meters. Giving us: [-0.1, 0.71, 0.605] for the left box, and [-0.1, -0.71, 0.605] for the right, green box. This seems to help our robot hit the center of the box!

Horizontal Pass through Filter

As you can see from the image below, our robot is placing the object location of the glue to be near the green dropbox

Clearly, this is incorrect, and means we need to apply a pass through filter along the horizontal axis. But is this X or Y? Well from the dropbox.yaml file above, we know this is the Y-axis, because the dropboxes are located at -0.71 and 0.71. Let's cut this down to -0.50 and 0.50

Conclusion

This has been a very comprehensive project--by far the most challenging in the course so far. To improve it further, it would be best to run the project in a native Linux enivronment, without a Virtual Machine -- due to much of the errors coming from lag, and the robot not fully grasping objects, or simply holding onto them for too long. There could also be more development done in detecting the glue object that appears in world2 and world3. It is a small object, so many of the filters keeping the noise out would often exclude it from our analysis.