10.04.2025

Text2Loc: A Smarter Way to Navigate With Words

MCML Research Insight - With Yan Xia, Zifeng Ding and Daniel Cremers

The Challenge of 3D Localization

Navigating a city without GPS and relying only on descriptions like “I’m near a black pole, west of a gray-green road” is easy for humans. However, AI struggles with this task, especially in autonomous robots and self-driving cars that rely on 3D point clouds - detailed digital maps of the environment made up of millions of tiny points. These points are captured using sensors like LiDAR, which scan surroundings to create a 3D representation of objects, roads, and buildings.

Traditional methods try to match each word in a user’s description (like “black pole” or “gray road”) to specific objects in the environment, called text-instance matching. That’s slow, unreliable, and not very human-like. Worse, when the description is a bit vague - or there are multiple similar objects - these systems fail to pinpoint the exact spot, which is often referred to as the “last mile problem”.

The recent paper “Text2Loc: 3D Point Cloud Localization from Natural Language”, developed by our MCML Junior Members Yan Xia, Zifeng Ding, our Director Daniel Cremers, and collaborators Letian Shi and Joao F. Henriques, takes a different approach by first retrieving relevant submaps and then refining the location using a hierarchical approach. This method speeds up localization and improves accuracy, making it a major step forward for text-based navigation and tackling the “last mile problem”.

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How Text2Loc Works

The proposed Text2Loc architecture consists of two tandem modules:

• Global place recognition: Given a text-based position description, Text2Loc first identifies a set of coarse candidate locations, “submaps,” potentially containing the target position. This is achieved by retrieving the top-k nearest submaps from a previously constructed database of submaps using the novel text-to-submap retrieval model.
• Fine localization: Text2Loc then refines the center coordinates of the retrieved submaps via the designed matching-free position estimation module, which adjusts the target location to increase accuracy.

Text Descriptions as Input

Instead of relying on precise coordinates, Text2Loc understands natural language descriptions such as:

• “The pose is on top of a gray road.”
• “The pose is west of a black vegetation.”

These descriptions allow for intuitive, human-like localization, making it possible for systems to process spatial information the way people naturally describe their surroundings.

Global Place Recognition (Text-to-Submap Retrieval)

Rather than searching for a single matching object, Text2Loc retrieves the most relevant submaps from a large 3D environment. This reduces the complexity of the search while increasing accuracy.

Fine Localization (Instances in Retrieved Submaps)

After retrieving relevant submaps, Text2Loc performs fine localization by estimating the precise position within each submap. Unlike previous methods, it does not use a text-instance matching module to explicitly link words in the description to objects in the environment.

Instead, Text2Loc applies a neural network that operates directly on the spatial and semantic features of the submap and the input text. The model jointly encodes these features using a hierarchical architecture that captures both coarse and fine-grained spatial relationships.

This approach allows the system to predict a location without requiring object-level matching, which simplifies training and reduces inference time. This enables last-mile localization, ensuring that the system can pinpoint a precise location even in dense, real-world environments where GPS might fail.

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Why Text2Loc is a True Innovation

Text2Loc introduces a new paradigm in text-based 3D localization. Unlike older approaches that struggle with direct text-object matching, this method simplifies the process while improving precision. Instead of processing every object individually, it retrieves relevant submaps, understands spatial relationships hierarchically, and refines the localization using a novel matching-free position estimation module.

By leveraging natural language and retrieval-based localization, Text2Loc enables AI to navigate the world the way humans do - through words. This innovation makes it incredibly useful for goods delivery and vehicle pickup, where precise, text-driven localization is essential.

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Read More

While this article introduces key concepts, the original paper explores detailed insights into global place recognition and fine localization. If you want to understand the full methodology behind Text2Loc, including its advantages over traditional approaches, check out the original paper published at the CVPR 2024, one of the highest-ranked AI/ML conferences.

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#blog #research #cremers

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