Robust Long-Term Visual SLAM Using Thermal Imagery

Core Concepts

Thermal imagery can enable robust visual SLAM in challenging environments, but requires overcoming significant challenges in feature extraction and place recognition due to dramatic appearance changes over time. This work presents a SLAM system that leverages learned feature descriptors and a specialized bag-of-words vocabulary to achieve reliable long-term localization and mapping using thermal cameras.

Abstract

The authors present an approach to enable robust long-term visual SLAM using thermal (LWIR) imagery, which poses significant challenges due to dramatic appearance changes over time.
Key highlights:

Thermal imagery suffers from inconsistent feature extraction and changing gradients over time, making traditional feature-based SLAM methods ineffective.
The authors collect a comprehensive dataset of thermal imagery, including 24-hour outdoor timelapses, paired day-night trajectories, and unconstrained sequences, with GPS ground truth.
They train a bag-of-words vocabulary using SuperPoint features matched with the Gluestick learning-based matcher, which demonstrates effective loop closure and place recognition across day-night transitions.
The authors integrate the Gluestick-based feature matching into an MCSLAM framework, showing good local tracking and the ability to relocalize against a previously built map.
Experiments demonstrate the limitations of existing SLAM systems on thermal imagery, and the effectiveness of the proposed approach in overcoming day-night appearance changes.
The authors conclude that their system enables reliable long-term SLAM using thermal cameras, paving the way for all-day autonomy in challenging environments.

Stats

The dataset includes:

10 static 24-hour outdoor timelapses with FLIR Boson thermal cameras
Paired day and night trajectories with RTK GPS ground truth
Additional unconstrained trajectories without ground truth

Quotes

"Existing feature-based methods [15] [17] [22], are notably less effective with infrared (IR) imagery. This ineffectiveness is due to reduced and inconsistent feature extraction in the short term, and inverting image gradients caused by the variations in LWIR energy across different objects in the long term."
"We show that inconsistent feature extraction causes the ORB [26] based place recognition schemes used in almost all SOTA visual SLAM systems [3] [25] [36] to be ineffective over temporal gaps of only a few hours."

Key Insights Distilled From

Towards Long Term SLAM on Thermal Imagery

by Colin Keil,A... at arxiv.org 04-01-2024

https://arxiv.org/pdf/2403.19885.pdf

Deeper Inquiries

How could the proposed approach be extended to leverage additional sensor modalities, such as RGB cameras or LiDAR, to further improve the robustness and accuracy of the SLAM system

To enhance the robustness and accuracy of the SLAM system by incorporating additional sensor modalities like RGB cameras or LiDAR, a multi-sensor fusion approach can be adopted. By integrating data from RGB cameras, the system can benefit from color information for better feature extraction and matching, especially in scenarios with varying illumination. LiDAR data can provide precise depth information, aiding in 3D mapping and improving the overall localization accuracy.
The fusion of thermal, RGB, and LiDAR data can enable a more comprehensive understanding of the environment. RGB data can assist in texture-rich areas where thermal imagery may lack distinct features, while LiDAR can contribute to accurate mapping in challenging lighting conditions. By combining the strengths of each sensor modality, the SLAM system can achieve higher resilience to environmental variations and improve performance in complex scenarios.

What other applications beyond robotics could benefit from the ability to perform reliable long-term localization and mapping using thermal imagery

The ability to perform reliable long-term localization and mapping using thermal imagery has applications beyond robotics. One significant application is in surveillance and security systems. Thermal cameras are effective in detecting intruders or anomalies in low-light conditions, and the capability for long-term SLAM on thermal imagery can enhance the tracking and monitoring of objects or individuals over extended periods. This is crucial for security operations in areas where traditional cameras may be ineffective due to poor visibility.
Another application is in environmental monitoring, such as in forestry management or wildlife conservation. Thermal imagery can provide valuable insights into animal behavior, habitat analysis, and vegetation health. Long-term SLAM using thermal data can facilitate continuous monitoring of environmental changes and help researchers and conservationists make informed decisions based on spatial data collected over time.

How could the training of the bag-of-words vocabulary be improved to better handle the specific challenges of thermal imagery, such as by explicitly incorporating day-night image pairs

To improve the training of the bag-of-words (BoW) vocabulary for handling the challenges specific to thermal imagery, explicit incorporation of day-night image pairs during training can be beneficial. By including pairs of images captured during different lighting conditions, the BoW model can learn to recognize and match features that exhibit significant variations in thermal appearance. This approach enables the vocabulary to adapt to the diurnal changes in thermal imagery, enhancing the system's ability to relocalize accurately across different times of the day.
Additionally, introducing a more diverse range of thermal imagery data during vocabulary training can enhance the model's robustness. By including images with varying temperatures, textures, and environmental conditions, the vocabulary can learn to generalize better and perform effectively in real-world scenarios with thermal data. Fine-tuning the vocabulary with a larger and more representative dataset can improve its performance in long-term SLAM applications on thermal imagery.