Madhu Vankadari

I am a 2nd year DPhil student at the University of Oxford, working under the supervision of Prof. Niki Trigoni and Prof. Andrew Markhem.

My undergraduate degree is in Mechanical Engineering at Rajiv Gandhi University of Knowledge Technologies and I never did my Masters Degree.

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I worked with many robots such as manipulators, ground and Aerail Vechicles. I aim to make these robots a little bit safer than today. Currently, I am working on large-scale localization and mapping problems which has potential applications in Autonomous Driving, Augmented and Virtual Reality areas.

Skills: Python | Tensorflow | PyTorch | ROS | Gazebo

Published Venues: ECCV(1) ✔ IJCAI(1) ✔ ICRA(3) ✔ IROS(3) ✔ CORL(2) ✔

Publications

2022 - 2020 | 2020 - 2018 | 2018 - before

In this paper, we show how to use a combination of three techniques to allow the existing photometric losses to work for both day and nighttime images

Self-supervised deep learning methods for joint depth and ego-motion estimation can yield accurate trajectories without needing ground-truth training data. However, as they typically use photometric losses, their performance can degrade significantly when the assumptions these losses make (e.g. temporal illumination consistency, a static scene, and the absence of noise and occlusions) are violated. This limits their use for e.g. nighttime sequences, which tend to contain many point light sources (including on dynamic objects) and low signal-to-noise ratio (SNR) in darker image regions. In this paper, we show how to use a combination of three techniques to allow the existing photometric losses to work for both day and nighttime images. First, we introduce a per-pixel neural intensity transformation to compensate for the light changes that occur between successive frames. Second, we predict a per-pixel residual flow map that we use to correct the reprojection correspondences induced by the estimated ego-motion and depth from the networks. And third, we denoise the training images to improve the robustness and accuracy of our approach. These changes allow us to train a single model for both day and nighttime images without needing separate encoders or extra feature networks like existing methods. We perform extensive experiments and ablation studies on the challenging Oxford RobotCar dataset to demonstrate the efficacy of our approach for both day and nighttime sequences.

We present what is thus, to our knowledge, the first system to perform simultaneous mapping and multi-person 3D human pose estimation from a monocular camera mounted on a single UAV.

Unmanned aerial vehicles (UAVs) have been used for many applications in recent years, from urban search and rescue, to agricultural surveying, to autonomous underground mine exploration. However, deploying UAVs in tight, indoor spaces, especially close to humans, remains a challenge. One solution, when limited payload is required, is to use micro- UAVs, which pose less risk to humans and typically cost less to replace after a crash. However, micro-UAVs can only carry a limited sensor suite, e.g. a monocular camera instead of a stereo pair or LiDAR, complicating tasks like dense mapping and markerless multi-person 3D human pose estimation, which are needed to operate in tight environments around people. Monocular approaches to such tasks exist, and dense monocular mapping approaches have been successfully deployed for UAV applications. However, despite many recent works on both marker-based and markerless multi-UAV single-person motion capture, markerless single-camera multi-person 3D human pose estimation remains a much earlier-stage technology, and we are not aware of existing attempts to deploy it in an aerial context. In this paper, we present what is thus, to our knowledge, the first system to perform simultaneous mapping and multi-person 3D human pose estimation from a monocular camera mounted on a single UAV. In particular, we show how to loosely couple state-of-the-art monocular depth estimation and monocular 3D human pose estimation approaches to reconstruct a hybrid map of a populated indoor scene in real time. We validate our component-level design choices via extensive experiments on the large-scale ScanNet and GTA-IM datasets. To evaluate our system-level performance, we also construct a new Oxford Hybrid Mapping dataset of populated indoor scenes

An attempt is made to solve this problem in this paper by proposing a deep meta-imitation learning framework comprising of an attentive-embedding net- work and a control network, capable of learning a new task in an end-to-end manner while requiring only one or a few visual demonstrations

The ability to apply a previously-learned skill (e.g., pushing) to a new task (context or object) is an important requirement for new-age robots. An attempt is made to solve this problem in this paper by proposing a deep meta-imitation learning framework comprising of an attentive-embedding net- work and a control network, capable of learning a new task in an end-to-end manner while requiring only one or a few visual demonstrations. The feature embeddings learnt by incorporating spatial attention is shown to provide higher embedding and control accuracy compared to other state-of-the-art methods such as TecNet and MIL. The interaction between the embedding and the control networks is improved by using multiplicative skip-connections and is shown to overcome the overfitting of the trained model. The superiority of the proposed model is established through rigorous experimentation using a publicly available dataset and a new dataset created using PyBullet. Several ablation studies have been carried out to justify the design choices

In this work, for the first time, we bridge the gap between single image representation learning and sequence matching through" SeqMatchNet" which transforms the single image descriptors such that they become more responsive to the sequence matching metric

Visual Place Recognition (VPR) for mobile robot global relocalization is a well-studied problem, where contrastive learning based representation training methods have led to state-of-the-art performance. However, these methods are mainly designed for single image based VPR, where sequential information, which is ubiquitous in robotics, is only used as a post-processing step for filtering single image match scores, but is never used to guide the representation learning process itself. In this work, for the first time, we bridge the gap between single image representation learning and sequence matching through" SeqMatchNet" which transforms the single image descriptors such that they become more responsive to the sequence matching metric. We propose a novel triplet loss formulation where the distance metric is based on" sequence matching", that is, the aggregation of temporal order-based Euclidean distances computed using single images. We use the same metric for mining negatives online during the training which helps the optimization process by selecting appropriate positives and harder negatives. To overcome the computational overhead of sequence matching for negative mining, we propose a 2D convolution based formulation of sequence matching for efficiently aggregating distances within a distance matrix computed using single images. We show that our proposed method achieves consistent gains in performance as demonstrated on four benchmark datasets.

In this paper, we look into the problem of estimating per-pixel depth map for monocular night images.

In this paper, we look into the problem of estimating per-pixel depth maps from unconstrained RGB monocular night-time images which is a difficult problem that has not been addressed adequately in the literature. The state-of-the- art day-time depth estimation methods fail miserably when tested with night-time images due to a large domain shift between them. The usual photo-metric losses used for training these networks may not work for night-time images due to the absence of uniform lighting which is commonly present in day-time images, mak- ing it a difficult problem to solve. We propose to solve this problem by posing it as a domain adaptation problem where a network trained with day-time images is adapted to work for night-time images. Specifically, an encoder is trained to generate features from night-time images that are indistinguishable from those obtained from day-time images by using a PatchGAN-based adversarial discrim- inative learning method. Unlike the existing methods that directly adapt depth prediction (network output), we propose to adapt feature maps obtained from the encoder network so that a pre-trained day-time depth decoder can be directly used for predicting depth from these adapted features. Hence, the resulting method is termed as “Adversarial Domain Feature Adaptation (ADFA)” and its efficacy is demonstrated through experimentation on the challenging Oxford night driving dataset. To the best of our knowledge, this work is a first of its kind to estimate depth from unconstrained night-time monocular RGB images that uses a com- pletely unsupervised learning process. The modular encoder-decoder architecture for the proposed ADFA method allows us to use the encoder module as a feature extractor which can be used in many other applications. One such application is demonstrated where the features obtained from our adapted encoder network is shown to outperform other state-of-the-art methods in a visual place recogni- tion problem, thereby, further establishing the usefulness and effectiveness of the proposed approach.

In this paper, we propose an unsupervised deep learning framework with Bayesian inference for improving the accuracy of per-pixel depth prediction from monocular RGB images.

In this paper, we propose an unsupervised deep learning framework with Bayesian inference for improving the accuracy of per-pixel depth prediction from monocular RGB images. The proposed framework predicts confidence map along with depth and pose information for a given input image. The depth hypotheses from previous frames are propagated forward and fused with the depth hypothesis of the current frame by using Bayesian inference mechanism. The ground truth information required for training the confidence map prediction is constructed using image reconstruction loss thereby obviating the need for explicit ground truth depth information used in supervised methods. The resulting unsupervised framework is shown to outperform the existing state-of-the-art methods for depth prediction on the publicly available KITTI outdoor dataset. The usefulness of the proposed framework is further established by demonstrating a real-world robotic pick and place application where the pose of the robot end-effector is computed using the depth predicted from an eye-in-hand monocular camera. The design choices made for the proposed framework is justified through extensive ablation studies.

In this paper we present a new depth and temporal-aware visual place recognition system that solves the opposing viewpoint, extreme appearance-change visual place recognition problem.

This paper proposes an end-to-end self-supervised feature representation network named Attentive Task-Net or AT-Net for video-based task imitation. The proposed AT-Net incorporates a novel multi-level spatial attention module to identify the intended task demonstrated by the expert. The neural connections in AT-Net ensure the relevant information in the demonstration is amplified and the irrelevant information is suppressed while learning task-specific feature embeddings. This is achieved by a weighted combination of multiple inter- mediate feature maps of the input image at different stages of the CNN pipeline. The weights of the combination are given by the compatibility scores, predicted by the attention module for respective feature maps. The AT-Net is trained using a metric learning loss which aims to decrease the distance between the feature representations of concurrent frames from multiple view points and increase the distance between temporally consecutive frames. The AT-Net features are then used to formulate a reinforcement learning problem for task imitation. Through ex- periments on the publicly available Multi-view pouring dataset, it is demonstrated that the output of the attention module highlights the task-specific objects while suppressing the rest of the background. The efficacy of the proposed method is further validated by qualitative and quantitative comparison with a state-of-the-art technique along with intensive ablation studies. The proposed method is implemented to imitate a pouring task where an RL agent is learned with the AT-Net in Gazebo simulator. Our findings show that the AT-Net achieves 6.5% decrease in alignment error along with a reduction in the number of training iterations by almost 155k over the state-of- the-art while satisfactorily imitating the intended task.

This paper presents a new GAN-based deep learning framework for estimating absolute scale aware depth and ego motion from monocular images using a completely unsupervised mode of learning.

This paper presents a new GAN-based deep learning framework for estimating absolute scale aware depth and ego motion from monocular images using a completely unsupervised mode of learning. The proposed architecture uses two separate generators to learn the distribution of depth and pose data for a given input image sequence. The depth and pose data, thus generated, are then evaluated by a patch-based discriminator using the reconstructed image and its corresponding actual image. The patch-based GAN (or PatchGAN) is shown to detect high frequency local structural defects in the reconstructed image, thereby improving the accuracy of overall depth and pose estimation. Unlike conventional GANs, the proposed architecture uses a conditioned version of input and output of the generator for training the whole network. The resulting framework is shown to outperform all existing deep networks in this field, beating the current state-ofthe-art method by 8.7% in absolute error and 5.2% in RMSE metric. To the best of our knowledge, this is first deep network based model to estimate both depth and pose simultaneously using a conditional patch-based GAN paradigm. The efficacy of the proposed approach is demonstrated through rigorous ablation studies and exhaustive performance comparison on the popular KITTI outdoor driving dataset.

In this paper we present a new depth and temporal-aware visual place recognition system that solves the opposing viewpoint, extreme appearance-change visual place recognition problem.

Visual place recognition (VPR) - the act of recognizing a familiar visual place - becomes difficult when there is extreme environmental appearance change or viewpoint change. Particularly challenging is the scenario where both phenomena occur simultaneously, such as when returning for the first time along a road at night that was previously traversed during the day in the opposite direction. While such problems can be solved with panoramic sensors, humans solve this problem regularly with limited field of view vision and without needing to constantly turn around. In this paper we present a new depth- and temporal-aware visual place recognition system that solves the opposing viewpoint, extreme appearance-change visual place recognition problem. Our system performs sequence-to-single matching by extracting depth-filtered keypoints using a stateof-the-art depth estimation pipeline, constructing a keypoint sequence over multiple frames from the reference dataset, and comparing those keypoints to those in a single query image. We evaluate the system on a challenging benchmark dataset and show that it consistently outperforms a state-of-the-art technique. We also develop a range of diagnostic simulation experiments that characterize the contribution of depth-filtered keypoint sequences with respect to key domain parameters including degree of appearance change and camera motion.

This paper presents a deep network based unsupervised visual odometry system for 6-DoF camera pose estimation and finding dense depth map for its monocular view

This paper presents a deep network based unsupervised visual odometry system for 6-DoF camera pose estimation and finding dense depth map for its monocular view. The proposed network is trained using unlabeled binocular stereo image pairs and is shown to provide superior performance in depth and ego-motion estimation compared to the existing stateof-the-art. This is achieved by introducing a novel objective function and training the network using temporally alligned sequences of monocular images. The objective function is based on the Charbonnier penalty applied to spatial and bi-directional temporal reconstruction losses. The overall novelty of the approach lies in the fact that the proposed deep framework combines a disparity-based depth estimation network with a pose estimation network to obtain absolute scale-aware 6- DoF camera pose and superior depth map. According to our knowledge, such a framework with complete unsupervised endto-end learning has not been tried so far, making it a novel contribution in the field. The effectiveness of the approach is demonstrated through performance comparison with the stateof-the-art methods on KITTI driving dataset

This paper presents a deep network based unsupervised visual odometry system for 6-DoF camera pose estimation and finding dense depth map for its monocular view

This paper looks into the problem of precise autonomous landing of an Unmanned Aerial Vehicle (UAV) which is considered to be a difficult problem as one has to generate appropriate landing trajectories in presence of dynamic constraints, such as, sudden changes in wind velocities and directions, downwash effects, change in payload etc. The problem is further compounded due to uncertainties arising from inaccurate model information and noisy sensor readings. The problem is partially solved by proposing a Reinforcement Learning (RL) based controller that uses Least Square Policy Iteration (LSPI) to learn the optimal control policies required for generating these trajectories. The efficacy of the approach is demonstrated through both simulation and real-world experiments with actual Parrot AR drone 2.0. According to our study, this is the first time such experimental results have been presented using RL based controller for drone landing, making it a novel contribution in this field

In this paper, a gradient decent based methodologyis employed to tune the Proportional-Integral-Derivative (PID)controller parameters for AR Drone quadrotor.

In this paper, a gradient decent based methodology is employed to tune the Proportional-Integral-Derivative (PID) controller parameters for AR Drone quadrotor. The three PID controller parameters, proportional gain (Kp), integral gain (Ki) and derivative gain (Kd) are tuned online while flying. The proposed technique has been demonstrated through two test cases. One is the way-point navigation and other is the leader-follower formation control. The experimental result as well as simulations result have shown for both the cases.

The main objective of this paper is to develop an autonomous robot that show the use of Q-learning for navigation in a complete unknown environment.

The main objective of this paper is to develop an autonomous robot that show the use of Q-learning for navigation in a complete unknown environment. This will calculate the shortest path from current state to goal state by analyzing the environment through captured images. Further the captured images will be processed through image processing and machine learning techniques. The proposed method also takes care of the obstacles present in that environment. Initially, the unknown environment will be captured using a camera. Obstacle detection method will be applied on it. Then the grid based map obtained from vision based obstacle detection method will be given to Q-Learning algorithm which will be further made live with motion planning.